This fungal toxin may poison cattle, pigs or poultry eating stored corn containing the fungus Fusarium tricinctum. The poisons belong to a group of chemicals called trichothecenes. In cattle, the toxin may cause multiple haemorrhages and sometimes death; in poultry, there may be mouth lesions.
(See TRIIODOTHYRONINE.)
(See THYROXINE.)
Tachycardia is a disturbance of the heart’s action which produces great acceleration of the pulse.
An increase in the rate of breathing due to some pathological condition, or an environmental or stress factor. (See BREATHLESSNESS; PARAQUAT poisoning.)
(See TAPEWORMS.)
Amputation of the tail (docking) is, or has been, undertaken for a variety of reasons. In the UK the Royal College of Veterinary Surgeons has ruled that docking a puppy’s tail is an unethical procedure except when it is done for prophylactic or therapeutic reasons. Under the ANIMAL WELFARE ACT 2006 and 2011, it is a prohibited mutilation in dogs, unless they are of certain breeds, and in Wales these breeds are specified. Once the tail is amputated (docked) a dog cannot be a show dog. If a tail is amputated for other reasons, a veterinary certificate is then required for the dog. Docking by lay persons is illegal. A Scottish study showed working breed dogs were at significantly greater risk of tail injuries than other breeds of dogs.
In cattle, amputation of the tail is illegal except following injury and must, except in an emergency, be undertaken by a veterinary surgeon. Pigs’ tails are often docked to prevent tail-biting but, legally, this should only be undertaken where other methods to control tail-biting have failed. Lambs’ tails are docked legally to prevent faecal soiling and FLY STRIKE (see under DOCKING; LAW; WELFARE CODES FOR ANIMALS).
In pigs this ‘vice’ can be of great economic importance. There are various reasons why it occurs: boredom, absence of bedding, and overcrowding (floor space of less than 1.5 m2 (5 sq ft) per pig), are regarded as conducive to tail-biting. High temperature and humidity are possible causes. Bitten tails require amputation or dressing if PYAEMIA is to be prevented. When tail-biting occurs it is best to remove from the group the one with lesions and those causing it.
Tail sores in pigs These may follow tail-biting by one or two pigs out of a large batch and, if untreated, can lead to pyaemia.
In six months, out of 135 pig carcases condemned in an Oslo abattoir, 56 (41.5 per cent) were affected with pyaemia – and of these, 43 (76.8 per cent) had tail sores.
This disease of pigs was first recognised in the Czech Republic and occurs throughout Europe. In the UK, it was made a NOTIFIABLE DISEASE in 1974. Its cause is an enterovirus. Experimentally, the incubation period is stated to be 12 days. Piglets three weeks old and upwards are affected; adult pigs may be infected but show no clinical signs. By no means all piglets in a litter or on a farm become ill, and the mortality is usually low. The main sign is weakness or paralysis of the hind-legs. There is little or no fever or loss of appetite. Recovery occurs in a proportion of animals which are hand-fed. The disease is present in Britain to a small extent and apparently may be associated with abortion.
A congenital condition in which there is abnormal flexure of the carpal and/or the tarsal joints (commonly called club foot). The problem may involve one or more limbs. There are two types: talipes VALGUS, where the animal walks on the inner side or part of the foot with the sole turned outwards and talipes VARUS, where the animal walks on the outer part or side of the foot and with the sole turned inwards.
(See ASTRAGALUS.)
A soft tick of the family Argasidae. (See TICKS.)
A rapid accumulation of blood or other fluid in the pericardial sac, compressing the heart and sometimes suddenly arresting its function.
One of the oldest pig breeds. There are now only 300 registered breeding females. The skin and hair are pale red to dark red mahogany, the snout longish and ears erect. The boar weighs 250 kg to 370 kg (550 lb to 815 lb) and sows 200 kg to 300 kg (440 lb to 660 lb). The Tamworth strain probably helped to produce the PIÉTRAIN breed. The litter sizes are smaller than those of LARGE WHITE PIGS and LANDRACE PIGS.
Tannin (tannic acid) is a non-crystallisable white or pale-yellowish powder, which is soluble in water and glycerine. It is prepared from oak-galls, and is found in strong tea or coffee. When brought into contact with a mucous surface, tannin causes constriction of the blood vessels. When brought into contact with many poisonous alkaloids it renders them temporarily inert by forming the insoluble tannate, and so is a valuable antidote.
Uses Tannic acid has been used in diarrhoea and dysentery in young animals, usually as CATECHU or kino – two vegetable drugs which contain a large amount of tannin. It is often administered, in the form of strong tea, as the first step in the antidotal treatment of poisoning by ALKALOIDS.
Tannic-acid jelly is a valuable burn dressing. It lessens the absorption of breakdown products from the burned area and hence diminishes the secondary effects of a serious burn. It is not suitable for extensive areas owing to the danger of liver damage if large quantities are absorbed.
Latin for shining carpet, the tapetum is a modified part of the choroid coat of the eye reflecting light in certain mammals, especially those, like cats, active in times of reduced daylight. (See EYE - COATS OF THE EYEBALL - THE CHOROID.)
An intestinal parasite commonly found in vertebrates. Their life-cycle requires two hosts, sometimes three. The presence of the adult worm may give rise to few if any signs or, on the other hand, to anaemia, indigestion, and nervous signs – or even to blockage of the intestine. The cystic stage of tapeworms may involve the brain. Tapeworms are of considerable public-health importance.
A typical tapeworm has a head or scolex, provided with suckers and, in some species, with hooks also.
Behind the scolex follows a neck, and behind that are the segments, each being called a proglottis. The segments nearest to the head are the smallest, and are immature. Next follow mature segments, and lastly the gravid segments containing eggs. These older segments fall off and are passed out of the host’s body in the faeces.
Taenia. This is the common genus of worms found in dogs and cats, and includes:
T. pisiformis (T. serrata) is one of the commonest. Its cystic stage, Cysticercus pisiformis, is found in rabbits and hares.
T. hydatigena (T. marginata) is the largest form, with mature segments wider than long. It may reach a length of over 5 m (16 ft). Its cystic stage, C. tenuicollis, occurs in the viscera of various animals, especially sheep, cattle and pigs. T. ovis is frequently mistaken for the last form, from which it can be distinguished only by microscopical examination. Its cysticercus, C. ovis, is found in the muscles and organs of sheep and goats. It is a small form, easily overlooked.
T. multiceps (T. coenurus) is a more delicate form than the others, semi-translucent. The intermediate stage is a coenurus, found in the nervous system of sheep and other ruminants and man.
T. serialis is a more robust form, its coenurus being found in rabbits and hares. Only one species is common in the cat, T. taeniaeformis (T. crassicollis). The cystic stage C. fasciolaris is found in the liver of rats and mice.
T. saginata is a tapeworm of man which produces cysticercosis infection in the muscles of cattle; this is C. bovis, known as measly beef. T. solium is another tapeworm of man, the intermediate stage of which (metacestode) is found in the skeletal and heart muscles of pigs, producing measly pork.
Diphyllobothrium. D. latum is the broad tapeworm of man, the dog and the cat. It is rare in Britain, but has a wide distribution. Several species are found, but this is the commonest. The life-history is interesting. The ciliated larva liberated from the egg is swallowed by a crustacean, Cyclops strenuus or Diaptonius spp., in which it becomes an elongated form with a terminal sphere containing three pairs of hooklets, called a ‘procercoid larva’. The crustaceans are swallowed by a fish, when the larva, migrating to the muscles, becomes an elongated infective larva called a ‘plerocercoid’. The fish is eaten by a suitable host, and the adults develop. In man, the tapeworm may attain a length of 18 m (60 ft), and it may cause a grave form of anaemia (bothriocephalus anaemia) associated with gastric and nervous symptoms.
D. mansoni is also widely distributed and has a similar life-history, but the infective stage is found in many hosts, including man, pig, and carnivores. It is common in frogs in Japan. The adult worm is found in carnivores.
Treatment of dogs infested with tapeworms is very important, because some of the species in their intermediate stages are dangerous to food animals. Farm dogs should never be allowed to harbour tapeworms. Routine use of ANTHELMINTICS is essential: a wide range is available, many based on PRAZIQUANTEL or DICHLOROPHEN. All faecal material passed should be destroyed.
Dipylidium caninum infests cats also; and may be transmitted by swallowing a flea.
In pigs, cattle and sheep cysts of the tapeworm Taenia hydatigena (which infests the dog and may occasionally attain a length of 5 m (16 ft)) may be so numerous in the liver that the latter ruptures, causing death.
Tapeworms in horses Three species occur in horses, all belonging to the genus Anoplocephala. A. perfoliata and A. mamillana are not uncommon in Britain, while A. magna is also sometimes encountered.
A. perfoliata, a stoutish worm with large head and no hooks, is a cause not only of unthriftiness but occasionally also of ileal and caecal obstruction, and/or INTUSSUSCEPTION, where numerous A. perfoliata are present. The infection may therefore be more serious than is generally supposed. The intermediate host is a mite. Diagnosis in the horse is the presence of tapeworm segments in faeces, or an accurate blood test.
Tapeworms in ruminants All the tapeworms of ruminants have four suckers and no hooks. In Moniezia the intermediate host is a free-living mite.
The segments of Moniezia worms are much broader than they are long. The worms may attain a length of several metres/yards, with a minute head little larger than a pin-head. More than 1,000 worms have been recorded from a single host. Numerous species have been recorded. H. giardi is found in Europe, Australia, and Africa and is from 1 m to 2 m (3 ft to 6 ft) long.
A closely related form, Thysanosoma actinoides, is found in North America. It is about 30 cm (1 ft) long, and is found in the liver. The sheep show general signs of malnutrition.
Bovine cystercercosis in Denmark On 14 farms with a history of this disease the source of infection on six of the farms was sludge from septic tanks applied to pasture or crops. In two herds the cattle grazed pasture near a sewage plant; while on three farms people defecating on pasture was a possible source. Those findings are typical wherever the infestation occurs.
Tapeworms in poultry A number of tapeworms have been found in poultry, of which the commonest are Davainea proglottina, which has a larval stage in slugs and snails and is widely distributed, and several species of Raillietina, with the larvae in house-flies, dung beetles and ants. The following are also common in many countries: Amoebotoenia, with larvae in earthworms; and Hymenolepis of various species, some of which may be very numerous in individual birds.
‘Measles’ in beef due to the presence of the cyst stage (Cysticercus bovis) of the tapeworm Taenia saginata, which is a parasite of man. Cattle swallow the eggs of the adult tapeworm, and these hatch in the intestines, liberating young embryos, which burrow until they settle in muscle fibre or connective tissues. Here they appear as small oval cysts, containing fluid, and each possessing the head of a potential tapeworm.
‘Measles’ in pork is due to the presence of the cyst stage (Cysticercus cellulosae) of the tapeworm of man, Taenia solium. It is extremely common among pigs in eastern lands, which have access to garbage and human faeces, from whence they pick up the eggs passed through the human intestines. The eggs undergo a development similar to those of the beef-measles tapeworm. Man may also himself harbour the cystic stage. According to the FAO, it is one of the 10 food-borne parasites with the greatest global impact.
Cysticercosis in man Very high sporadic infection rates have been found in Africa with Taenia saginata and T. solium, the two tapeworms of major importance in man. Where T. solium is present, serious human infections with the cysticercus stage may be observed, as well as mild infections with the adult tapeworm. When it occurs in beef cattle, the cysticercus of T. saginata is a major economic problem and a serious obstacle to the export of meat.
A single human carrier of T. saginata led to an outbreak of cysticercosis among cattle on a large farm in the USA.
Coenurosis (gid or sturdy) in sheep and goats This disease is caused by the pressure of cysts of the tapeworm Taenia multiceps on cells of the brain (or spinal cord).
Sheep become infested by swallowing the unhatched eggs, excreted in a dog’s faeces, while grazing. In the digestive tract the eggs hatch, and pass via the bloodstream to various parts of the body; only those reaching the central nervous system develop. Here they form small cysts, each containing one tapeworm head: this larval stage is known as Coenurus cerebralis. Over a period of months, each cyst increases in size, and more heads are budded from the lining membrane of the translucent cyst wall. Eventually a single coenurus may contain 50 or 100 or more tapeworm heads (scolices) projecting inwards.
The life-cycle is completed if a dog eats the head of an infested sheep.
Signs These include impairment of vision, a staggering or high-stepping gait, circling and standing with head lowered, raised, or pressed against an object. Backward somersaults have been recorded. Recumbency and opisthotonus may occur. A softening of the bone of the skull, due to internal pressure of the cysts, is found in a proportion of cases.
Diagnosis Where there is no softening of the skull, a guide to the location of the cyst may be given by interpretation of the neurological signs as indicated by the sheep’s behaviour. An intradermal test has been used: 0.1 ml of cyst fluid is injected into a shaved area of skin. Thickening of the skin within 24 hours indicates the presence of a cyst in the animal.
Treatment Physical removal of the cyst may be attempted. The sheep is anaesthetised and, in the absence of any skull softening, a trephine used to remove a disc of bone 1.5 cm (0.6 in) in diameter. Draining the fluid from the cyst before its removal obviates the need to enlarge the hole. The cyst is then removed completely. (If this is not done, the remaining cyst wall is apparently capable of replacing the fluid.)
Hydatid disease is caused by the cystic larval stage of the microscopic tapeworm Echinococcus granulosus in Britain and E. multilocularis which is more severe and found especially in Eastern Europe. In both, the dog and fox are the usual hosts. Eggs released from tapeworm segments passed in the faeces by these animals are later swallowed by grazing cattle, sheep and horses, which may become infested also through drinking water contaminated by wind-blown eggs.
People become infested through swallowing eggs attached to inadequately washed vegetables, and possibly eggs may be inhaled in dust or carried by flies to uncovered food. The handling of infested dogs is an important source. In man and other intermediate hosts the larvae form cysts which can be found in different organs such as liver, lung, etc., leading to debilitating and often fatal disease. Medical treatment is usually ineffective and surgical incision is the best chance for success.
There have been successful campaigns to control human hydatid disease in both Cyprus and Iceland, by compulsory treatment and/or banning of dogs.
Swallowed eggs hatch in the intestines and are carried via the portal vein to the liver. Some remain there, developing into hydatid cysts; others may form cysts in the lungs or occasionally elsewhere, e.g. spleen, kidney, bone-marrow cavity, or brain. Inside the cysts, brood capsules containing the infective stage of the tapeworm develop and, after 5 or 6 months, can infest dog or fox.
In Wales, where the incidence of hydatid disease is relatively high, farm dogs and foxhounds are important in its spread.
About seven people are known to die from this disease in England and Wales each year – this figure would probably be higher if diagnosis were less difficult. Condemnation of sheep and cattle offal from this cause costs hundreds of thousands of pounds annually. Routine worming of dogs is essential for control. Infestation can be brought back to the EU from mainland Europe under the PET TRAVEL SCHEME. All dogs returning to the UK must be treated for tapeworms.
E. granulosus and E. multilocularis are far from being typical tapeworms, as they have only three or four segments and a total length of a mere 3 mm to 9 mm (0.12 in to 0.35 in), so that the dog-owner will not notice the voided segments.
A problem of diagnosis also arises, as this worm’s eggs are indistinguishable from those of Taenia tapeworms. Examination of a dog’s faeces following dosing with arecoline would reveal the intact tapeworm. However, this drug has now been replaced by more modern drugs which destroy the tapeworm but leave it unrecognisable.
DICHLOROPHEN, PRAZIQUANTEL, NITROSCANATE, and BENZIMADAZOLES are used for treatment.
Equine hydatidosis in Britain is caused by a strain of Echinococcus granulosus which has become specifically adapted to the horse as its intermediate host, and is often referred to now as E. granulosus equinus. This apparently is of low pathenogenicity for man.
In a survey covering 1388 horses and ponies examined at two abattoirs in the north of England, 8.7 per cent were infected. Prevalence of infection was closely related to age, rising from zero in animals up to 2 years old to over 20 per cent of those over 8 years old.
66 per cent of the infected animals had viable cysts.
Treatment of human patients According to the FAO, E. granulosus and E. multilocularis are two of the 10 food-borne parasites with the greatest global impact. Hydatid disease is one of the rare parasitic conditions that can be treated by surgery. However, the result is often incomplete, with frequent local recurrences or accidents of secondary dissemination. Repeated interventions are often mutilating and do not guarantee a definite cure. MEBENDAZOLE is reported to have been used successfully in patients. (See also HYDATID DISEASE.)
(See ASPIRATION.)
Recently applied tar, in the form of asphalt on roads and pavements, often causes irritation between a dog’s toes, causing the animal to lick or bite the part. The tar must be removed with a bland fat or oil. Crude tar should never be used on an animal’s skin. (See also PITCH POISONING.)
These include the Chilean rose spider (Grammostola spatulatus). If found lying on its back, this creature should not be assumed to be dead, but merely moulting. In the UK, tarantulas are being kept as pets; in Australia wild tarantulas (‘red-back’ spiders) bite a few hundred people each year. An antivenin is available. (See also PET ANIMALS ACT 1951; PETS, CHILDREN’S AND EXOTIC.)
The bone of the bird’s lower shank between the tibia and the bones of the foot, formed by the fusion of the tarsus and metatarsus bones. It is only found in birds, and from it in some species a SPUR is produced, which is the remnants of the fifth toe.
An operation for producing union of upper and lower eyelids. It is performed as a permanent measure after enucleation of an eyeball; and sometimes as a temporary expedient to give protection to an ulcerated or perforated cornea. (But see LENSES, CONTACT)
The hock. (See under BONES.)
Tartar is the concretion that often forms upon the crowns and upon the necks of teeth, as well as upon exposed portions of the roots. The material is of a brownish, yellowish or greyish colour, and consists chiefly of phosphate of lime which has been deposited from the saliva, making plaque, with which are mixed numerous food particles and bacteria of a harmful nature. Tartar is most often seen in the mouths of dogs and cats, although the herbivorous animals may also be affected.
It is important that the formation of tartar is prevented by feeding a suitable diet and that accumulated tartar be removed from time to time; if it is allowed to collect for an indefinite period the gums shrink before the advancing deposit, the root becomes exposed and ultimately affected, and the tooth loosens and falls out. There are, also, generally signs of systemic disturbance, such as a bad smell from the breath, indigestion from inability to feed properly and, in bad cases, great irritability and loss of condition. Prevention in CARNIVOROUS animals is provided by supplying ‘meat on the bone’. The animals use their teeth to pull muscle meat off the periosteum, which allows the fibrous connections to clean their teeth. (See TEETH, DISEASES OF.)
An Australian breed of beef cattle, similar to the Murray Grey but developed from Aberdeen Angus and White Shorthorns.
The WATTLE of a goat.
(See CNEMIDOCOPTIASIS.)
This special sense is dependent upon the taste buds, located in the crevices of the papillae. The taste buds have minute projections – the endings of nerve fibres. It is necessary for the purpose of taste that the substance should be dissolved in a fluid, and it seems that this is one of the functions of the saliva. The sense of taste is closely associated with the sense of smell. (See TONGUE; SMELL; JACOBSON’S ORGAN.)
Identifying marks or numbers may be applied to animals by tattooing. On black skins, tattooing is not an effective method, and the use of nose prints has been tried for cattle. The tattooing of dogs is widely practised in France (where it is compulsory for the Kennel Club’s register of pedigree dogs), and in Canada and the USA.
Tattooing, usually in the ear, is used to identify cattle, pigs, sheep and goats. It is not entirely free from the risk of introducing infection, e.g. blackquarter, tetanus. FREEZE-BRANDING and MICROCHIPPING are alternative methods. (See also DANGEROUS DOGS ACT 1991.)
An amino acid essential to maintain the health of cats, and which must be provided in the food. In the USA, feeding of cats on canned dog foods is reported to have led to a taurine deficiency, resulting in degeneration of the cat’s retina.
However, a level of taurine in the cat’s diet sufficient to prevent degeneration of the retina may be insufficient to prevent the heart disease, dilated cardiomyopathy (DCM). Most modern proprietary cat diets contain adequate amounts of taurine. It may assist in preventing FELINE LOWER URINARY TRACT DISEASE (FLUTD).
Taurine supplementation may be required for large breeds of dogs. In zoos, maned wolves (Chrysocyon brachyurus) require extra taurine in the diet compared to similar-sized dogs.
Taxis is the method of pushing back into the abdominal cavity a loop of bowel which has passed through the wall as the result of a rupture or hernia.
(See TUBERCULOSIS.)
LYMPHOCYTES from the thymus gland concerned with cell-mediated immunity. (See IMMUNE RESPONSE.)
(See EYE; for ‘soapy’ tears, see ALGAE POISONING; see also NAPHTHALENE POISONING.)
Tear-staining of the face in the dog may be due to atopic disease or (and also in rabbits) to blockage of a lacrimal duct.
(See under MOLYBDENUM; ‘PEAT SCOURS’.)
(See under VASECTOMY.)
One of the most important defences against bovine mastitis, as almost all infection enters the cow’s udder by this route. The constant production and shedding of cells lining the canal helps to remove pathogenic bacteria. (See also MASTITIS IN COWS; ORIFICES, IMMUNITY AT.)
(See under LINER, TEAT-CUP.)
First practised by a veterinary surgeon in 1916, this has proved a useful measure for the control of mastitis in cattle. Teats are dipped, usually after milking, to help prevent streptococcal and staphylococcal infection. However, pre-milking teat dipping has been advocated as a means of reducing coliform mastitis. Results in the UK are reported as variable.
The liquid chiefly used for the purpose is an iodophor, but good results can be obtained with hypochlorite teat dips containing 1 per cent available chlorine. (See under MASTITIS IN COWS.)
This is seen in piglets reared under intensive conditions, and is sometimes accompanied by skin necrosis affecting the limbs. Inadequate bedding and abrasive concrete may be contributory factors.
(See under MAMMARY GLAND; also VIRAL INFECTIONS OF COWS’ TEATS; MASTITIS.)
(See BOVINE HERPES MAMMILLITIS; TEAT NECROSIS, VIRAL INFECTIONS OF COWS’ TEATS.)
The breed is found mainly in the Teesdale area of County Durham, Northern England. It has been established for over 200 years and is found mainly in Britain and North America. It has long-stapled wool. The Teeswater ram was crossed with the DALESBRED ewe or SWALEDALE ewe to produce the MASHAM breed.
Teeth are highly calcified structures that penetrate the lining of the mouth. Most mammals have two sets of teeth, baby/deciduous and adult/permanent; some just have adult teeth. These are attached to the underlying bone by a sheet of periodontal ligament surrounding each tooth root. The tooth support structures and alveolar bone can be destroyed by periodontal disease (see MOUTH, DISEASES OF) causing tooth loss. Carnivores and omnivores typically have smaller, shorter and fewer teeth than herbivores, some of which have prolonged tooth growth (e.g. large animals such as horses and cattle) or continuous tooth growth (rabbits, guinea pigs and chinchillas) allowing for considerable tooth wear from prolonged chewing. Some fishes and reptiles have teeth that are fused directly to the underlying bone, and which are shed and replaced at intervals throughout life.
Tooth patterns and shapes vary, but the basic mammalian arrangement is to have three incisor teeth, one canine tooth, four premolar teeth and three molar teeth in each quadrant of the mouth, making 44 teeth in total. The number is reduced in many species; dogs typically have 42, man 32 and cats 30, although there is individual variation — expected teeth may be missing and others can be duplicated producing ‘supernumerary teeth’.
Teeth developed in connection with the mucous membrane of the mouth, being actually calcified papillae. They are implanted in sockets or ‘alveoli’ in the upper and lower jaws, being only separated from actual contact with the bone by a layer of ‘alveolar periosteum’.
The incisors are implanted in the incisive bones of the upper jaw, and in the anterior part of the mandible; they are situated in the front of the mouth, and used for grasping and cutting. They are absent from the upper jaw of cattle, sheep, and goats, as well as other ruminating animals.
The canines are situated behind the incisors, and are used mainly for fighting purposes, being most developed in carnivores and omnivores. They are useless to the domesticated herbivorous animals, and in them are usually of small size. They are not present in the upper jaws of ruminants, and in the lower jaws have the shape and function of incisors.
The molars are the remaining teeth, situated further back in the mouth. They are used mainly for chewing, and are specially adapted for this purpose by having broad strong irregular tables or grinding surfaces. The term ‘cheek teeth’ is often applied to these teeth since, strictly speaking, they are composed of ‘premolars’, which are represented in the milk dentition, and ‘molars’, which are not so represented. (See DENTITION.)
Each tooth has a portion covered with enamel, the ‘crown’; a portion covered with cement, the ‘root’; and a line of union between these 2 parts known as the ‘neck’. A constriction occurs at the neck in the temporary incisors of the horse, in the incisors of the ruminants, and in incisors and molars of the dog and cat; in the remaining teeth there is no such constriction.
Structure Teeth are described as having a crown and one or more roots, based on human dentition. Teeth consist of four tissues. In the middle of the tooth is the ‘pulp’, occupying the ‘pulp cavity’. It is soft and gelatinous, well supplied with blood vessels and nerves, and is large in the young tooth. It nourishes the remaining tissues, and forms dentine for as long as the pulp cavity is open. In later life it is small or absent, the pulp cavity having filled with dentine formed from the pulp. The ‘DENTINE’ forms the bulk of the tooth. It is hard, yellowish, or yellowish-white in colour, and is surrounded in the crown by enamel, and in the root by cement. The ‘enamel’ consists of a comparatively thin layer of a brilliant white colour and extremely dense and brittle, which forms a cap to the dentine, or, in hypsodont (high-crowned) teeth, it is arranged in layers throughout it. Carnivores and omnivores have brachydont (low-crowned) teeth. Herbivores have a mixture of hypsodont and brachydont teeth, e.g. in the horse, the incisors and the cheek teeth are hypsodont and the canines are brachyodont.
The ‘cement’ is always the outermost layer of a tooth, being formed on the outside of the dentine in the root, and of a bone-like tissue, filling up the irregular spaces and hollows of the crown. The implanted part of a tooth is fixed into the socket by a layer of vascular fibrous tissue, which serves as the periosteum both of the tooth root and of the lining of the alveolus. It is known as the ‘alveolar periosteum’.
Enamel is the hardest tissue in the body, and consists mainly of phosphate of lime. It is composed of prisms placed side by side, with one end resting on the dentine and the other end towards the free surface in a simple tooth, such as the canine of a dog. Cement is practically of the same structure as bone, without possessing Haversian canals.
Arrangement and form For times of cutting of the various teeth, see DENTITION.
Most diseases or disorders affecting the teeth are associated with pain or discomfort, which results in absence of appetite, capriciousness in feeding, or other disturbances.
Irregularities In certain cases, the incisor or molar teeth develop out of their normal positions in the jaw, with the result that perfect apposition between the upper and lower teeth is not possible, and the rate of tooth wear is not uniform. In other instances, extra or ‘supernumerary’ teeth are formed; in the incisor region these are usually placed behind the arch of normal teeth, while extra molars may be found as projections from the gums on the inside or the outside of the line of normal teeth.
When the temporary teeth are shed, it sometimes happens that the permanent teeth erupt irregularly to one side or behind the temporaries, and are distorted accordingly. This frequently happens in puppies and, to a lesser extent, in the herbivores (cattle, sheep). In the former, trouble is likely to be experienced between 8 weeks and 5 or 6 months, and in young horses at 6 weeks and 3½ years of age. In such cases it is necessary to extract any temporaries which persist, so that the permanent teeth can arrive in their proper places in the mouth.
In dogs frequently, in sheep sometimes, and in other animals less commonly, there may be a discrepancy in length between the upper and lower jaws. When the upper jaw is too long, the condition is known as an ‘overshot jaw’, and when the lower jaw projects too far forward, it is popularly spoken of as an ‘undershot jaw’. In bulldogs, pugs and other breeds of dogs with very short upper jaws the undershot condition is accepted as normal, while in certain breeds with extremely long upper jaws, such as the GREYHOUND and show collie, overshot jaws are very common.
Abnormal wear, which is due to malformations of the jaws, to excessive softness of the teeth, or to the direction of the teeth, is another mechanical cause of tooth disorder. (See SOIL-CONTAMINATED HERBAGE with reference to sheep.) Even though the main components of teeth, enamel and dentine, are hard, they wear away as they are used. Wear from functional use (attrition) should be quite slow in carnivores but is rapid in herbivores, particularly grass-eaters.
Abnormal wear is mainly a disorder of hypsodont teeth seen in herbivores, which are continuously erupting. This is most important in the cheek teeth of the horse, which erupt at approximately a tenth of an inch a year and in normal conditions are abraded at about the same rate by eating relatively hard silicates in herbage. Thus if a cheek tooth in as horse is lost or displaced, the tooth opposing the gap will not be worn down at the same rate as the rest of the cheek teeth in that row. The tooth will not only be worn down less but it will ‘super erupt’. This creates a condition known as ‘step mouth’, where, instead of the teeth all being the same level, they are arranged with some higher than others, somewhat like steps.
The cheek tooth rows in the horse consist of six teeth, are continually being ground together to chew the food and are thus continuously being abraded. The cheek teeth tables are not flat but at an angle, where the buccal aspect of the upper cheek teeth is lower than the palatine aspect and the buccal aspect of the lower cheek teeth is higher than the lingual aspect. This creates a cheek teeth angle up to 35º in a normal horse. However, if the angle is greater than that there are problems of abnormal wear called ‘shear mouth’. If the upper cheek teeth are not symmetrical with the lower cheek teeth rows in a rostral/caudal direction, there will be formation of a local dental overgrowth, as there is not accurate apposition between the rostral and caudal cheek teeth. These traditionally are known as ‘hooks’. The most common foca dental overgrowths are linked with brachygnathia, commonly called ‘parrot mouth’ or ‘overshot jaw’. The overgrowths are formed on the rostral upper cheek teeth and the lower cheek teeth. The opposite occurs with prognathia, commonly called ‘sow mouth’, ‘monkey mouth’ or ‘undershot jaw’.
The horse has anisomatic cheek teeth rows. The occlusal surfaces of the upper cheek teeth rows are 25 per cent wider than the occlusal surfaces of the lower cheek tooth rows. If the diet of the horse does not contain sufficient long fibre requiring a wide excursion of the mandible during the chewing motion, sharp enamel points will be formed on the buccal aspects of the lower cheek tooth rows. These are self-perpetuating as the excursion of the mandible is then adversely affected and it will lead to cheek ulceration.
During the chewing motion the occlusal surfaces may not be worn evenly so that the occlusal surface will not be flat but will form a wave. The opposite occlusal surface will also wear unevenly as a mirror image. This is called ‘wave mouth’.
Signs In most of these instances the animal affected (almost always a member of the horse tribe), instead of chewing its food and swallowing it in the usual way, rolls it round and round in the mouth until it collects into a sodden mass, often about the size of a couple of fingers, and puts it out of the mouth instead of swallowing it. (See QUIDDING) Pain may be shown when the hand is passed along the outside of the cheek, especially when pressure is put upon the line of teeth.
Quidding will also be shown by horses which have gaps between their cheek teeth, called DIASTEMA (plural diastemata). Food becomes packed into these gaps which causes gingivitis and eventual erosion of the alveolar socket. This is the most painful dental condition seen in the horse.
Treatment Rasping the teeth by means of a hand-held tooth-rasp will reduce small or minor irregularities, and bring the teeth back into their proper function. If the abnormal wear has been excessive, the correction will have to be made over time, normally at three-monthly intervals. As a rule, horses’ teeth should be checked at least every 12 months. A shorter time interval should be advised in cases of more advanced dental disease, particularly in older horses. Diastemata, particularly in younger horses, which are causing quidding will need to be treated. This is usually carried out by ‘widening the diastema’ with a motorised burr. This has to be carried out with great care to ensure the burr does not enter the pulp cavity and cause death of the tooth. Tooth death can also be caused by excessive heat and so great care must always be taken when using motorised equipment.
Caries is not synonymous with tooth decay, although the term – borrowed from human dentistry – is often used in veterinary practice to include all tooth decay.
Caries is the destruction of the tooth enamel and invasion of the dentine by bacteria, which feed on carbohydrates, releasing acids which dissolve the minerals out of teeth allowing the bacteria to penetrate and destroy the inner tooth structure, resulting in the formation of a cavity. Caries cavities tend to form when there are free sugars in the diet, although starch can also support such bacteria.
Neck lesions in cats’ teeth A painful condition affecting middle-aged to elderly cats, characterised by cavitation of the necks of teeth, out of sight as it is just below the gingival margin edge. This makes extraction difficult because of the risk of breakage of crowns.
Inflammations of the periosteum lining the root cavity of a tooth are common. They may be due to small particles of food getting forced down into the socket of the tooth, to fractures or fissures of the teeth, to caries, tumour formation, depositions of tartar, and to certain specific diseases, such as actinomycosis, etc.
Signs These vary from a slight redness of the gum around the root of the tooth, which is painful when pressed by the finger, to a large suppurating tract running alongside the root of the tooth down into its socket, and perhaps through the skin to the outside or into one or other of the sinuses. Abscess formation in the tooth socket may take place, and the abscess may burst into the mouth, to the outside through the skin, or up into a sinus. In many cases there is a distinct bulge of the surface above the diseased tooth, which may give to the face a one-sided appearance.
Treatment The affected tooth or teeth must be extracted, and the areas of suppuration cleansed and curetted if necessary. The cavity usually has to be packed with antiseptic gauze afterwards for a few days until it begins to fill by healthy granulation tissue.
Periodontal disease is a name for chronic infection of the periodontal membrane. It is one form of inflammation of the periosteum, or alveolar periostitis. It causes loosening and shedding of the teeth, pain, failure to masticate, and loss of weight. This is quite common in elderly cats and often leads to the extraction of all molars, premolars and incisors, with the retention of the canines to maintain the conformation of the jaws.
Odontomata are tumours formed in connection with the root of one tooth, or they may be found in the jaw, sinuses, or even involving part of the nasal passage, and be composite or compound, when multitudes of small rudimentary teeth are present. They cause swelling and bulging of the surface of the face, and can only be treated surgically.
‘Broken mouth’ is important in hill sheep. (See under ‘BROKEN MOUTH’.)
Fractures of the canine teeth in dogs are not uncommon. If the pulp is exposed, subsequent infection can lead to a painful abscess. Extraction of the remainder of the tooth obviates this but, for show dogs or guard dogs, is undesirable. Metal crowns have been applied to dogs’ teeth, but are liable to be dislodged. Apisectomy, or removal of the apex or end of the root of a canine tooth to seal the root canal, often acts as a successful salvage operation, even in a working dog.
Tooth transplantation has been used in veterinary practice but the results are seldom lasting, due to root resorption and bone replacement. Fracture of the transplanted tooth is likely after a couple of years or so.
Tooth deformities Teeth are easily damaged during their formation, resulting in misshapen (dilacerated) crowns or roots, or areas where the tooth surface has not formed properly. Enamel hypoplasia/dysplasia/aplasia causes partially formed, abnormally formed, or missing teeth. Similarly, the internal tooth structure may be abnormal (dentine dysplasia).
Tooth resorption is a more common cause of cavities in many species. While cats are predisposed to this, cases occur in dogs, rabbits, chinchillas and larger animals like deer and cattle. Some cases are due to inflammation but many are idiopathic (unknown cause). Resorption of the tooth surface in areas exposed in the mouth results in discomfort or pain in the sensitive dentine. Resorptions buried in the jaw and not exposed to the inside of the mouth do not appear to cause significant pain.
Tooth pulp disease Inside the tooth mineralised structure is living tissue containing nerves and blood vessels, the dental pulp. This can become damaged, infected and/or die, resulting in endodontic disease (endo = inside, odont = tooth). Injuries of the tooth can directly expose the pulp causing inflammation (pulpitis). A minor blow can disrupt the blood supply to the tooth causing it to die, with release of pigments; the tooth becomes discoloured. If not treated, infection may spread to the base of the tooth, resulting in an abscess.
Dental deposits There is a tendency for accumulation of deposits on teeth. Salivary glycoproteins attach to clean teeth creating an extremely thin layer termed pellicle. This can become stained by pigments from food. Pellicle allows the attachment of bacteria that secrete a slimy material creating DENTAL PLAQUE. Dental plaque is initially translucent, making it difficult to see, but it sometimes absorbs pigments making it visible; application of dyes (e.g. from disclosing tablets/solutions) allows it to be seen. Initially, the bacteria involved are mainly Gram-positive aerobes that do not cause significant inflammation in adjacent tissues. As undisturbed plaque matures, other bacteria become involved with a tendency for growth of Gram-negative and anaerobic organisms that act as periodontal pathogens, causing local inflammation and tissue damage (gingivitis and periodontal disease). Damage is progressive, especially if the human or animal has a weak or disordered immune system. Many bacteria die and become calcified, creating hard mineralised deposits known as DENTAL CALCULUS or TARTAR. Dental calculus is itself inert, but has a rough surface that allows further dental plaque accumulation.
Dental deposits can be prevented from becoming established by regular and thorough tooth brushing. Established dental deposits can be removed using a combination of TEETH SCALING and polishing. Antibiotics are not effective in preventing dental plaque as organisms growing in a biofilm are far less susceptible than those living planktonically (free floating in liquid).
Porphyria gives rise to a pink or brown discoloration of teeth. (See under BONE, DISEASES OF.)
Toothache common and very unpleasant. In the dog, it often rubs its mouth along the ground, paws at its nose or mouth, works its jaws, salivates, and may whine or moan. A veterinary surgeon will offer a diagnosis and initiate the necessary treatment.
Tooth discolouration The teeth of most mammals are typically considered white, although there is considerable variation. Various things can result in discoloration including stains (almost any colour but mainly black and brown), deposits such as bacterial plaque (often difficult to detect unless the layer is thick) and tartar (dental calculus; mineralised dead dental plaque) which can be white or yellow/brown. External stains and deposits can be professionally removed and then dental hygiene measures and regular tooth brushing should help prevent return.
Internal tooth discoloration may be due to ageing (typically darkening in colour), injury with pulp death (grey/brown/purple particularly towards the tip of the tooth), metabolic disease (e.g. porphyria) and deposition or absorption of chemicals (yellow/brown teeth in dogs, cat and children given tetracyclines during tooth formation).
It has been estimated that between 60 per cent and 70 per cent of culling of ewes is on account of their teeth. A small percentage will involve loss of molars or incisor wear, but the vast majority will be incisor loss.
Ewes have been treated for ‘bite correction’ by means of an electric grinder, a practice that originated in Australia. The procedure has been strongly condemned on welfare grounds.
(See also ‘BROKEN MOUTH’.)
Deposits can be removed from teeth using a combination of scaling and polishing. Stained pellicle and immature dental plaque can be removed by tooth brushing or polishing. If dental calculus is present then the removal of the hard deposits is termed ‘de-scaling’ or ‘scaling’. This can be done using hand instruments with small sharp blades, dental hand-scalers and curettes, and/or mechanical instruments such as sonic or ultrasonic scalers. Mechanical scalers reduce the effort required to clean off deposits but have the disadvantage, that during the scaling, an aerosol of water droplets is formed, with a variable amount of periodontal debris spattered from the patient’s mouth, which may contain viruses and/or bacteria – a danger for operator, assistant, or subsequent patient unless precautions are taken. An aerosol of mouth flora can remain airborne for up to 30 minutes following scaling and can spread a significant distance.
It is recommended that: (1) the working area should be well ventilated – preferably with forced air extraction; (2) masks should be worn at all times by anyone in the working area; and (3) a 0.2 per cent chlorhexidine solution should be used as the coolant supplied to the scaling equipment.
This is a polytetrafluoroethylene and produces fumes on heating that are given off by kitchen utensils during use. These can be lethal for birds. Bird cages must be kept away from kitchens, nor should birds be allowed to fly in kitchens. (See also ‘FRYING PAN’ DEATHS; ‘KITCHEN DEATHS’.)
A genus of nematodes within the Family Trichostrongylidae, which was previously called OSTERTAGIA. There are three species: Teladorsagia circumcincta (formerly O. circumcincta) in sheep abomasum, T. boreoarcticus (muskoxen) and T. davtiani (Canadian Maritime sheep).
(See RADIO ‘PILLS’.)
The resting phase in the cycle of hair growth.
Triethylenemelemine, a gametocide which, in America, has been used in field trials for the control of birds. The chemical is mixed with corn, and has the effect of making the male bird infertile. The birds continue to defend their territories and nest, but do not produce any young.
(See THROMBOEMBOLIC MENINGOENCEPHALITIS.)
This may follow a brain tumour or infection, as occurs in BOVINE SPONGIFORM ENCEPHALOPATHY and RABIES, for example. A horse may become bad-tempered as the result of EQUINE VERMINOUS ARTERITIS. Poisoning may cause frenzy or aggressiveness, e.g. BENZOIC ACID poisoning in the cat. (See also BRAIN DISEASES; STRESS; FUCOSIDOSIS.)
(See under HOUSING OF ANIMALS; HEAT EXHAUSTION; TROPICS, LIVESTOCK PRODUCTION IN THE.)
Body temperature is controlled by the heat-regulating centre in the brain – the hypothalamus, which also influences blood circulation, secretion of urine, and appetite – all three of which have a bearing on body temperature.
Heat is produced by the muscles and by the digestive organs, and during very cold weather or exercise, heat from the former increases, while that from the liver and other digestive organs decreases. The animal may also absorb heat from the sun’s rays.
Heat is lost by evaporation of water, and by sensible heat loss (see under HEAT LOSS). Water loss is achieved via the lungs and the skin, e.g. by panting and sweating. (The dog is, for all practical purposes, a non-sweating animal apart from the pads of its feet, and has to rely mainly on panting.)
Diurnal variations in body temperature are normal; in the early hours of the morning it is usually at its lowest, and at its highest in the late afternoon.
For ordinary practical purposes the usual average temperatures of animals are given as follows:
Horses |
38.0° C (100.5° F) |
Cattle |
38.9° C (102.0° F) |
Sheep, goats |
40.0° C (104.0° F) |
Pigs |
39.7° C (103.5° F) |
Dogs |
38.3° C (101.0° F) |
Cats |
38.6° C (102.0° F) |
Rabbits |
38.2° C (100.8° F) |
Fowls |
41.6° C (106.9° F) |
Small birds |
42.5° C (108.6° F) |
Elephants |
36.4° C (97.6° F) |
Camels |
37.5° C (99.5° F) |
Temperature-taking The most satisfactory place is within the rectum. In females the thermometer may also be inserted into the external part of the genital canal; as a rule, the vaginal temperature is about half a degree higher than the rectal temperature, so that when a series of temperatures is to be taken, one site or the other should be selected.
With dogs and cats, one person should hold the animal, preferably on a table, while another inserts and holds the thermometer. In each animal, after the bulb of the thermometer has been lubricated with a little soap or Vaseline, etc., the tail is raised vertically by the left hand, and the thermometer is inserted through the anal ring and into the rectum, by a screwing movement if any resistance is encountered. It is held in position for 30 seconds, or one minute, according to the make of the thermometer, and then withdrawn. With a piece of cotton-wool any adherent faeces are wiped away, and the temperature is read off. Subsequently, the thermometer should be washed in cold water, and a cold solution of disinfectant used to disinfect it.
For purposes of temperature stress research, American scientists use a special ear thermometer in cattle. As in similar medical research, this tympanic thermometer is more reliable than the rectal thermometer, and can sense changes as small as 0.05° C (1/50° F). A device is available for cattle, which measures ruminal temperature remotely and transfers the data to a computer where it can be analysed. The temperature changes can be used to detect infection, the rise of OESTRUS and the fall at calving. (See PARTURITION.)
Temperature in disease A high temperature is one of the classic signs of fever, and in greater or less measure accompanies practically all acute cases of disease. A comparatively steady rise in temperature is as a rule succeeded by a correspondingly steady fall, and is to be looked upon as a more favourable sign of the natural course of a disease than when the temperature rises and falls with greater suddenness. The reduction of temperature in simple fevers is in almost all cases much slower than the rise. A wavering temperature, which shows little tendency to come down to normal, generally indicates that there is some active focus of disease, such as an abscess, which the body cannot overcome. A sudden rise in temperature in an animal which has shown a steady fall previously is an indication of a relapse or recurrence of the disease. (See also FEVER; HYPERTHERMIA; HEAT-STROKE; TROPICS, LIVESTOCK PRODUCTION IN THE.)
A fall in temperature may be occasioned by great loss of blood, starvation, collapse, or coma; it is characteristic of certain forms of kidney disease. Certain chronic diseases in which emaciation is marked are also associated with a subnormal temperature. (See also HYPOTHERMIA.)
Temperature, near calving time A healthy cow – even though showing the familiar signs – is unlikely to calve during the next 12 hours if her temperature is 39° C (102° F). This is a useful guide to herdsmen. (See also under FEVER; HOUSING OF ANIMALS, etc.)
(See CONTROLLED ENVIRONMENT HOUSING.)
(See VACCINE.)
Tenderness is pain that is felt only when a diseased or injured part is handled.
Tendon is the dense, fibrous, slightly elastic cord that attaches the end of a muscle to the bone or other structure upon which the muscle acts when it contracts. Tendons are composed of bundles of fibrous tissue, white in colour, and arranged in a very dense manner, so as to be capable of withstanding great strains. Some are rounded; some are flattened into ribbons; others are arranged in the form of sheets; while those of a fourth variety are very short, the muscle fibres being attached almost directly on to the bone or cartilage which they actuate. Most tendons are surrounded by sheaths lined with membrane similar to that found in joint cavities, i.e. synovial membrane. In this sheath the tendon glides smoothly over surrounding parts. The fibres of a tendon pass into the fibres of the periosteum covering a bone, and blend with them. One of the largest tendons in the animal body is the Achilles tendon, which runs from the large muscles at the back of the stifle down to the point of the hock; it is often called the ‘hamstring’, and is the structure that is injured in the condition known as ‘hamstrung’.
(See also under MUSCLES; SPRAINED TENDONS.) In most cases the injuries to which tendons are liable are in the nature of minute lesions in which fibres have been torn across through over-extension of the tendon as a whole. Accompanying these there are often slight haemorrhages or extravasations of blood into the substance of the tendon, and the tendon itself is thickened at the injured part or, when severe, practically over the whole of its length. At the same time, a certain amount of damage has usually been sustained by the tendon sheath, or by its lining, and an unusually large amount of the lubricating synovial fluid is thrown out, which fills the tendon sheath to the point of dilatation, causing it to stand out on the surface of the limb.
When recovery occurs, the swelling subsides, fluid is absorbed, and the broken ends of the fibres become attached by strands of fibrous tissue to other intact fibres nearby. Pain disappears, and the animal becomes sound. Sometimes, however, permanent thickening results. (See also KNUCKLING.)
Certain of the tendons of the horse’s limb are liable to become ruptured when subjected to great or sudden strains. Suture of the ruptured ends of the tendon has given good results when performed early, and when a sufficient amount of support can be provided by splints or other means. (See CARBON FIBRE IMPLANTS.)
Severing of tendons in dogs’ legs has been successfully treated. (See also TENOSYNOVITIS.)
Straining to pass urine or faeces with little or no result.
Tenosynovitis is inflammation of the tendon and its sheath. It affects the legs of broiler chickens and is usually caused by a virus. Tendons may enlarge and cease to function. (See also SYNOVITIS.)
The surgical severing of a tendon.
A new NSAID which inhibits two enzyme pathways and is, therefore, more effective in certain circumstances than the usual NSAIDs.
Tetra-ethyl pyrophosphate, used in agriculture as a pesticide, is a potential danger to livestock. A Texas rancher diluted one volume of TEPP with water to make 120 volumes, and sprayed 20 head of cattle. All were dead within three-quarters of an hour. Signs of poisoning in a puppy comprised drowsiness, muscular incoordination and vomiting. The antidote is ATROPINE sulphate.
(See MONSTER.)
An agent which has effects on the dam resulting in congenital abnormalities in the offspring. It may be chemical, environmental, plant or infectious. (See TERATOGENIC.)
Teratogenic agents, called teratogens, are those known to cause congenital defects when the pregnant mother is exposed to them. The most notorious is thalidomide but there are many others, not all of them drugs: alkaloids found in some plants, e.g. hemlock, viruses and radiation can all be teratogenic.
Teratoma is a developmental irregularity in which the embryo, instead of growing normally in the uterus, develops structural defects or, in extreme cases, develops into a seriously deformed fetus. The latter are comparatively common in cattle, and give rise to difficulty at parturition. ‘Teratology’ is the study of congenital deformities. (See also under TUMOURS.)
A relatively common condition. (See under ILEITIS; ‘WET TAIL’ IN HAMSTERS.)
A term especially used in sheep but also cattle. It often involves a ram with good meat potential serving usually a cross-bred animal developed for size and milk to produce offspring specifically designed to be raised for meat but not for breeding. In sheep, terminal sires are especially rams of the CHAROLLAIS SHEEP, SUFFOLK SHEEP and TEXEL SHEEP breeds. In cattle, terminal sires include bulls of the CHAROLAIS, BRITISH BLUE and LIMOUSIN breeds.
Whitish, ant-like insects of the tropics. Some species feed on wood, damaging buildings.
Control Heptachlor and chlordane.
A small aquatic turtle, of which the diamond-backed terrapin (Malaclemys terrapin) or the red-eared terrapin (in USA called ‘slider’) (Pseudoemys scripta) is typical. Males are smaller than females, with the diamond-backed reaching about 14 cm (5½ in) to the female’s 32 cm (9 in), and the red-eared reaching 20 cm (8 in) in the male and 32 cm (22 ins) in the female. They are popular domestic aquarium pets; however, they should be handled with care as cases of salmonella poisoning in members of households in which they are kept have occurred.
A breed of dog originally from Flanders. EPILEPSY has been recorded in some individual dogs.
(See TALFAN DISEASE.)
Testicle (testis) is the essential male generative gland or gonad which, along with the epididymis and its associated structures, lies in the scrotum in each of the domesticated animals.
Normally, in the fetus or soon after birth, the testicle, guided by the fibrous cord known as the gubernaculum, moves down from a position close to the kidney to a ‘cooler climate’ in the scrotum. Into this it is pulled by the gubernaculum, which either fails to lengthen or actually shortens.
In some animals, e.g. foals, one or both testicles may re-ascend through the inguinal canal. This occurs occasionally in pigs, in which a returning testicle has been known to become vestigial or atrophied by the age of six months.
In certain of the wild animals, such as the rat, rabbit and chinchilla, and in many tropical animals, e.g. the elephant, the testes are found in the abdominal cavity, either permanently or temporarily between periods of sexual activity. In the foal the testes appear in the scrotum usually very soon after birth, but they are subsequently drawn up into the abdomen, and do not reappear until between 5 or 6 months and 10 to 12 months. In a certain proportion of cases the testes are retained in the abdomen until 2 years of age, and then descend into the scrotum; in a number of cases they do not descend at all. The name ‘rig’, or ‘cryptorchid’, is applied to such animals, and the condition is known as ‘cryptorchidism’. (See CRYPTORCHID.)
The testis consists of a dense fibrous coat, the ‘tunica albuginea’. Blood vessels run throughout the fibrous tissue, and nourish microscopic tubules, lined by layers of specialised cells which form the spermatozoa. The tubules, known as ‘seminiferous tubules’, are connected with each other near the centre of the testes, and communicate with the coiled tubes of the epididymis, from which the vas deferens connects with the urethra at the opposite end. In the epididymis the sperms mature. The ‘SPERMATIC CORD’, which consists of the vas deferens, spermatic artery, veins and nerves, enclosed in the layer of serous membrane (tunica vaginalis), passes upwards through the inguinal canal and enters the abdomen, where it runs back to the region of the neck of the urinary bladder, where it opens into the urethra. Along the course of the urethra are the openings of the ducts from the secondary sexual glands – seminal vesicles, prostate, and bulbo-urethral glands – which pour out a secretion which mixes with, nourishes and protects the masses of spermatozoa coming from the testes.
Externally, the testicle is covered by a layer of serous membrane, lying immediately outside the tunica albuginea, and known as the tunica vaginalis propria, which also covers the epididymis. On the outside of this tunic is the tunica vaginalis communis, or the parietal layer. Outside this is a fairly thick layer of scrotal fascia, in which is deposited the ‘cod-fat’ of the bullock and wedder. A strong reddish, fibro-elastic tunica dartos forms the next outermost layer, and provides the septum between the right and left pouches of the scrotum. Finally, on the outside, there is the practically hairless, thin, elastic, oily-feeling skin of the scrotum.
Functions The essential function of the testis is to produce sperms. (See SPERMATOZOA) Between 60 and 80 million sperms are discharged at each copulatory act by the stallion at the beginning of the breeding season. Since a stallion may serve more than 100 mares during the season, many of them upon two separate occasions, the testes are, obviously, extremely active organs, and make a considerable demand upon the vitality of the body generally. The necessity for a recuperative period in breeding males will also be obvious.
The other function of the testis is that associated with the male sex-hormones, which produce the secondary sexual characteristics, such as the arched neck and great body size of the stallion, the broad forehead, massive development of horns, and deep voice of the bull, the horns of the ram, and the tusks of the boar, etc., as well as the desire for sexual intercourse. The chief hormone is testosterone.
(See also REPRODUCTION; ENDOCRINE GLANDS; ARTIFICIAL INSEMINATION.)
During service, an irritable mare may kick a stallion and rupture one of the testes, or seriously injure it. Damage may also be occasioned to these organs by the bites of dogs when fighting, by gores from cattle, or by injuries from the tusks of boars, gunshots, etc. However, infection is probably most common.
Orchitis, or inflammation of the testis, may be the result of infection (e.g. by Actinobacillus seminis, Brucella abortus, B. suis, Corynebacterium pseudotuberculosis, tuberculosis) or of trauma which – if the skin is broken – may itself lead to infection. Necrotic orchitis in the bull has been caused in Britain by actinobacillosis. The testis, being enclosed in a fibrous, comparatively non-elastic capsule, is not able to swell to a great extent, although the loose tissues of the scrotum often do. The scrotum becomes reddened in animals which have unpigmented skin in the inguinal region, and the whole area is very painful to the touch.
In rabbits, abscessation of the testicle is commonly encountered after fights between rival bucks, due to infection with the ubiquitous Pasteurella multocida.
Treatment Antibiotics or other therapy may be needed to deal with an infection. However, castration may be necessary to prevent infection spreading internally.
Epididimytis (See under main dictionary heading and RAM EPIDIDYMITIS.)
Hydrocele is a local oedema affecting usually one tunica vaginalis, and distending that side of the scrotum with fluid, but painless. It is most frequently encountered in the dog, although it may affect other animals.
Hypoplasia (See under INFERTILITY.)
Tumours affecting the testicle and/or scrotum include CARCINOMA, SARCOMA, FIBROMA, PAPILLOMA, SEMINOMA and SERTOLI-CELL TUMOUR.
Torsion (See under SPERMATIC CORD, TORSION OF.)
The hormone, secreted by the testicle, which controls development of the secondary sex organs, sex characteristics and libido. (See ENDOCRINE GLANDS; HORMONES.)
(See LABORATORY TESTS.)
Tetanus (lockjaw) is a specific disease of the domesticated animals and man, caused by Clostridium tetani, which obtains access to the tissues through a wound. Horses are most commonly affected. The organism is present in most cultivated soils, especially those that have received heavy dressings of farmyard manure.
In certain districts, tetanus is so common that it is usual to take precautions by inoculating horses with antitoxin whenever they receive even comparatively slight wounds, and always before castration or major operations. Unvaccinated lambs born to unvaccinated ewes are lost each year after docking and castration, or before the umbilicus (navel) has closed after birth, from tetanus.
Cl. tetani is an anaerobe, i.e. it thrives only in an absence of oxygen. Its serious effects are produced by a toxin, which is absorbed into the general circulation and exerts its effects upon the nervous system of the brain and spinal cord. This toxin is one of the most powerful known.
Deeply punctured wounds, from which oxygen is excluded, are much more serious than even large superficial wounds, the surfaces of which are exposed to the action of sunlight and fresh air. Wounds from picked-up nail wounds, cracked heels, injuries from the tines of stable-forks, pitch forks, etc., are examples of wounds which often become contaminated with Cl. tetani. Tetanus may occur in an animal which has had a slight wound which appeared to heal without any complication. It may follow tattooing. Cases are encountered where no wound can be found on the surface of the body, nor is there any history of an accident; such cases are probably the sequel to injuries inflicted by worms in the intestinal wall, or to slight scratches from unusually hard or rough herbage.
Intramuscular injections are a potential route of infection when sterile precautions are neglected.
Signs
Horses become stiff and disinclined to move. There is difficulty in turning the head round to the side, and the fore-legs are splayed outwards as though to enable the unfortunate animal better to retain its balance.
The ears may be turned in towards each other.
If the head is lifted sharply up, by placing the hand under the chin, the haw or third eyelid (nictitating membrane) is seen to flicker across the eye to an extent much greater than usual.
Fixed clenching of the jaws, or trismus, which has been responsible for the popular name given to tetanus (i.e. lockjaw), is not always in evidence in the early stages of an attack.
The tail may be held out quivering and OPISTHOTONOS may be evident.
During the course of an attack, faeces and urine are usually withheld, and digestive disturbances may occur, sometimes resulting in fatal collections of gas in the large intestines.
(See HYPERAESTHESIA.)
Cattle Early signs include a raising of the tail-head and, in some cases, bloat. The gait becomes stiff and the animal may have difficulty in feeding because it cannot easily lower its head because of stiffness in the neck. Trismus (lockjaw) is a late sign. Tetanus in cattle is not, however, at all common; occasionally outbreaks occur, possibly due to rough, abrasive feed which allows entry of the infection through the gut.
Sheep The signs are similar to those in cattle. As the disease progresses, standing is difficult; the affected animals lie on their sides, rapidly become tympanitic, and die after a very short illness. In lambs after castration or docking, the disease is very rapid in its effects, and several are affected at the same time.
Pigs Tetanus is not common.
Dogs The owner may notice something peculiar about the eyes and mouth, and either stiffness or recent lameness. Later, the limbs are usually stretched out as far from each other as possible, in a sawhorse position. Squinting and grinning are common, but closure of the jaws is not always in evidence. When it is present it is complete, and death practically always follows. Hyperaesthesia is also very marked. The ears may be bent inwards (as in the horse).
Treatment Farm animals should be placed in a darkened loose-box, away from noise, and with food and water placed at a new level which they can reach despite their stiffness.
If nursed at home, a dog should be in a room where there are no bright lights, noise, television, or family activity.
Tetanus antiserum, penicillin and muscle relaxants (such as acepromazine, which can obviate exhaustion and save life) are all needed. Treatment must also include glucose saline injections, e.g. in a dog which cannot drink or eat; and large animals similarly. (See DEHYDRATION, NORMAL SALINE.)
Prevention Vaccination is effective, and should be used in all horses, sheep, goats and camelids as the infection is common worldwide. Injection of pregnant dams will allow antibodies in the colostrum to be passed to the offspring so that when it is ingested passive immunity will be provided to the offspring. On land where tetanus is rife, cattle should also be immunised.
Lambs are given antitoxin on the day of docking or castration. Vaccine can be injected at a different site on the same occasion.
Horses The usual practice is to give 2 injections at an interval of 4 to 6 weeks, with a booster dose 6 or 12 months later. Further booster doses may be required. It is practicable to vaccinate pregnant mares so that later their newborn foals will be protected against tetanus infection via the navel. (See also under IMMUNITY.)
Prognosis In the absence of first-class nursing and intensive care, not many animals (other than cattle) recover from tetanus.
If an animal regains the ability to drink, that can be regarded as a favourable sign.
(See ANTITETANIC SERUM.)
Tetany is a condition in which localised spasmodic contraction of muscles takes place. There may be twitching or convulsions. Tetany occurs when the level of blood calcium falls below normal. (See also under PARATHYROID GLANDS; HYPOMAGNESAEMIA; TRANSIT TETANY; MILK FEVER; RABIES.)
The Cruel Tethering Act 1988 made it illegal to tether a horse, ass or mule in such a way as to cause suffering. The animal must have enough to eat and be supplied with fresh water regularly. The tether must not be able to cause injury, e.g. by being too tight or too short. This is now covered by the Animal Welfare Act 2006. These acts cover unnecessary suffering, supply of feed and water and the question of the tether causing harm. In some situations, abandonment may be considered. In comparison with free-range horses, those tethered were more likely to have eye lesions, vertical hoof cracks, lameness and limb pain, and less likely to have a low condition score or tangled mane and tail. In the same study tethered horses were less likely to have shelter or access to water.
Tetracyclines are bacteriostatic antibiotics with a wide range of activity which includes Gram-positive and Gram-negative bacteria, certain protozoa, Rickettsia, and Mycoplasma. Tetracyclines are absorbed from the gut, but oral administration may upset the gut flora. They are irritant when injected.
Tetracyclines cause fluorescence in bone and teeth. In late pregnancy or in young growing animals, high dosage can result in teeth discoloration and can interfere with the formation of enamel. (See CHLORTETRACYCLINE, DOXYCYCLINE, OXYTETRACYCLINE.)
(See IMIDAZOLINE COMPOUNDS.)
A transparent and nearly invisible protozoan living in water. It is able to digest and so remove Listeria monocytogenes. It can also ingest but not digest Salmonella spp.
Tetraiodophenolphthalein is used in radiography of the gall-bladder and bile-ducts for diagnostic purposes.
A complex congenital heart condition which consists of:
1. stenosis of the pulmonary valve;
2. a defect of the septum which separates the two ventricles;
3. the aorta overriding both ventricles;
4. marked hypertrophy of the right ventricle.
The condition can occur in all species but is rare and the signs can be quite vague, for example, in kittens there may be failure to thrive and inability to cope with exercise. More serious defects result in death of the animals soon after birth. The incidence is high in some dog breeds such as KEESHONDS.
(adjective, Tetraplegic)
(See QUADRIPLEGIA.)
Compounds containing four pyrrole rings. They can have three carbon bridges (linear tetrapyrroles - bilanes) such as HAEM breakdown products (BILIRUBIN); and phycobilins (found in CYANOBACTERIA) of four carbon bridges (cyclic tetrapyrroles) for example PORPHYRINS (HAEM); chlorines (CHLOROPHYLL); and corrins that have three carbon bridges and a direct connection between two pyrrole rings.
Texas fever is a tick-borne disease. (See BABESIA - BABESIOSIS.)
Signs Stained urine (red-water), high temperature, no appetite, and constipation followed by diarrhoea. Cerebral signs may be evident. The animal dies within three to 10 days. On post-mortem examination the blood is bright red and abnormally fluid, while the tissues are paler. The spleen is enlarged from two to four times its normal size and is reddish-brown (‘anthrax spleen’). The liver is swollen and pale and the gall-bladder is distended with thick, viscid, dark-coloured bile. The muscles are normal.
The chronic form is similar but milder, and occurs in late autumn. Recovery is frequent, but convalescence is long (although it is stated to be very short in Argentine cattle).
Treatment is fairly effective. Imidocarb is one of several proprietary preparations that have replaced the trypan blue formerly used.
Transmission is by the following ticks:
Boophilus (Margaropus) annulatus (North America)
B. microplus (South America)
B. australis (many countries)
B. argentinus (South America)
B. calcaratus (Asia)
B. decoloratus (South Africa)
Rhipicephalus appendiculatus (South Africa)
R. evertsi (South Africa)
R. bursa (North Africa)
Haemaphysalis punctata (Europe)
A Dutch breed of sheep from Texel, and the most common breed in Europe. Noted for its milk production, it has good growth rate and meat potential. It has a white fleece with no wool on head or legs and no horns. It has a white face with a black nose. It is thick set and used as a TERMINAL SIRE for meat, fleece weight is 3.5 kg to 5.5 kg.
(See TRANSMISSIBLE GASTROENTERITIS OF PIGS.)
A part of the brain consisting of two large ovoid structures at the base of the cerebrum. (See under BRAIN.)
Thallium sulphate has been used in poison baits to destroy rats, ants and other pests, and accidental poisoning in domestic animals may occur. Less dangerous substances have largely replaced it. Thallium poisoning in dogs gives rise to gastroenteritis, profuse vomiting and severe pain. If death does not immediately follow, there may be a brick-red discoloration of lips, skin of groin or axilla. Hair begins to fall out. In human medicine, thallium poisoning has been successfully treated with prussian-blue.
A sheep between first and second shearing. (See under SHEEP, NAMES GIVEN ACCORDING TO AGE, SEX, ETC.)
Infection with tick-borne parasites of the Theileridae.
The parasites vary in shape, some being spherical, others ovoid, pear-shaped, or elongated rod-like. Division by binary fission within the blood corpuscle may occur. Sexual multiplication occurs within the tick which transmits the parasite when it bites a new host.
There are several species in cattle and in sheep, including:
T. parva (EAST COAST FEVER in tropical Africa).
T. mutans (Benign bovine theileriosis).
T. lawrencei, causing CORRIDOR DISEASE.
T. annulata, causing MEDITERRANEAN FEVER.
(See also TZANEEN DISEASE.)
(See MALIGNANT THEILERIOSIS OF SHEEP AND GOATS.)
Theine is the alkaloid which gives its stimulant properties to tea. It is the equivalent of CAFFEINE.
(See EYEWORMS.)
Theobromine is the alkaloid upon which the stimulant action of cocoa and chocolate depends. It stimulates heart muscle and the central nervous system, causing increased activity and raised heart rate. Horses fed a supplement of vitamins and minerals incorporated in a material containing ground cocoa shells have tested positive for this alkaloid. CHOCOLATE POISONING is not uncommon in dogs.
A stimulant found naturally in tea leaves. It is available in tablet form for the treatment of BRONCHITIS and CONGESTIVE HEART FAILURE in dogs.
The mapping of temperature over surfaces. Infra-red thermography, using a camera, has been tested in the diagnosis of orthopaedic lesions in horses.
Subject to the loss of characteristic properties when heated.
This was the first of the benzimidazoles to become widely available in the 1960s in the UK for farm animals. (See ANTHELMINTICS.)
A product licensed for the stabilisation of feline hyperthyroidism. Prior to surgery or for the long-term treatment of hyperthyroidism. It controls the production of thyroxine and triiodothyronine.
Thiamine hydrochloride, or vitamin B1. A secondary deficiency occurs in bracken poisoning and horse-tails poisoning in horses, and in pigs due to the enzyme, thiaminase. Thiaminase-producing bacteria have been isolated from sheep dying from polioencephalomalacia (cerebro-cortical necrosis (CNN)). (See also ‘CHASTEK PARALYSIS’.)
Thiaminase is present to a varying degree in raw fish. Accordingly, fish should be cooked before it is fed to cats, etc.
Signs of thiamin deficiency include loss of appetite, a staggering gait and muscular spasms.
Treatment Thiamin injections are often effective in CCN.
A technique widely used to separate out mixtures of different substances. It is performed using a sheet of plastic, glass or aluminium foil coated with a thin layer of absorbent material such as silica gel, aluminium oxide or cellulose (blotting paper). The technique is usually used to identify compounds present in a mixture or to establish the purity of a substance.
Groups of sows or gilts lose weight, usually in the middle or later stages of pregnancy, and remain emaciated for perhaps six months or more. Prolonged under-feeding may eventually result in some sows being unable to cope with adverse conditions encountered at times of stress, e.g. weaning. It has also been suggested that infestation with the stomach worm Hyostrongylus or with the nodular worm Oesophagostomum may be a cause. The use of sow stalls, in which animals cannot move away to escape draughts, is another possible cause.
A relatively non-toxic salt, which is similar to cyanide but contains sulphur instead of oxygen. It is produced in the body as a detoxicating mechanism. It occurs in brassicas and continued ingestion by herbivores (ruminants, tortoises) can cause toxicity by producing GOITRE.
This was a widely used anaesthetic for horses, dogs and cats but has been superseded by more modern anaesthetics. It is administered intravenously, as an aqueous solution of the sodium salt; other routes cause necrosis of the tissues.
A benzimidazole anthelmintic not now available in the EU and USA.
An antibiotic used as a topical application for the treatment of conditions involving such bacteria as E. coli, Pseudomonas spp. and Proteus spp.
An antithyroid agent which lowers the rate of metabolism by inhibiting the oxidation of iodine thus preventing the formation of THYROXINE. It has been used as a growth promoter; such use is banned in the EU. It has used as a thyroid depressant in HYPERTHYROIDISM.
A goitrogenic agent whose action on the thyroid is the same as for THIOURACIL. It is used in industry as a photographic fixative. It is also known as naphythyl antu, a rat poison, which causes oedema of the lungs. It is dangerous to domestic animals and birds.
(See WATER AND WATERING OF ANIMALS; DIABETES MELLITUS; SALT POISONING; COMPULSIVE POLYDIPSIA.)
Thogoto virus is a cause of abortion in ewes in Africa. It was first isolated from a tick, Rhipicephalus appendiculatus, near Thogoto in Kenya. In one flock of some 600 Dorper ewes, more than 200 aborted over a two-month period.
The thoracic duct is the large lymph vessel which collects the contents of the lymphatics proceeding from the abdomen, hind-limbs, part of the thorax, etc., and which discharges its contents into the left innominate vein. (See aspiration under PARACENTESIS.)
Draining off from the thorax of the fluid found in certain diseases of the chest. (See aspiration under PARACENTESIS.)
A congenital abnormality where two malformed fetuses joined at the thorax.
A congenital fissure in the chest wall. (See CHEST.)
A surgical operation involving opening of the chest cavity.
(See CHEST.)
(See STRAMONIUM.)
This is the breed used for racing. All thoroughbreds are descended from three famous Middle Eastern sires, bought to England in the 17th and 18th centuries. The thoroughbred stud book is closed and no artificial insemination is allowed. Thoroughbreds are normally 15 to 17 HANDS high. They are commonly bay, chestnut or grey in colour, although black animals are sometimes seen. They normally start racing at about two-years-old. The Derby is a race for three-year-olds. All animals are said to be born on 1 January of the year in which they are born. Therefore, in the UK, thoroughbred breeders try to breed foals as early as possible in the year so that they are well developed as soon as they are sold or start to race. The stud season historically starts on St Valentine’s day (14 February).
Thorough-pin is a distension of the sheath of the deep flexor tendon in horses and ponies where it passes over the arch of the tarsus (hock). It is characterised by swellings, one on either side of the hock, about the level of the ‘point of the hock’ (summit of the tuber calcis), and lying in front of the strong Achilles tendon.
Thread-worm is a popular term for oxyuris worms. (See ROUNDWORMS.)
(See EPHEMERAL FEVER.)
One of the essential amino acids. It is found in low quantities in feed ingredients of plant origin. It is an important component of collagen and elastin fibres.
(See PHARYNX; also under LARYNX; NOSE AND NASAL PASSAGES.)
Throat diseases Most of these will be found under separate headings such as choking; larynx, diseases of; tonsillitis. For ‘sore throat’, see PHARYNGITIS.
This is a rare, congenital disorder of the blood, occurring in man and dogs, in both sexes (compare HAEMOPHILIA). It arises from a defect of the platelets, and gives rise to prolonged bleeding resulting in anaemia. It has been described in foxhounds, otterhounds, etc.
Infestation with mites from the Family Thrombiculidae. The most common is Neotrombicula autumnalis (formerly Thrombicula autumnali), the HARVEST MITE. Their orange larvae parasitise animals, man and some ground nesting birds, and may also cause CANINE SEASONAL ILLNESS (See MITES, PARASITIC.)
These are the blood PLATELETS that are involved in clotting. (See BLOOD.)
A condition of the blood in which the number of platelets is below normal. Causes include viral infections, poisoning, auto-immune disease. The signs may include petechial haemorrhages and fever.
An infection caused by Histophilus somni (previously Haemophilus somnus) in growing calves, resulting in them appearing dull, sleepy and usually dying. It is often called the ‘SLEEPER’ SYNDROME.
The formation of a blood clot (THROMBUS) which detaches itself from its point of formation and then moves on to other blood vessels, where it lodges when it cannot pass through them. The sites vary but can be the brain, heart, lungs, kidney, limbs or other tissues or organs. This then plugs the circulation to part or all of an organ (an EMBOLISM) and can lead to other signs. The damage depend on whether or not there is a sufficient COLLATERAL CIRCULATION. If there is any infection in the blood clot, it will also be spread to the other organ(s).
A coagulation disorder caused by a failure of ADENOSINE DIPHOSPHATE release from blood platelets. A condition seen in BASSET HOUNDS.
The blocking of a blood vessel by a blood clot. It may follow atheroma, or some injury to the vessel. In cats, thrombosis of the femoral arteries is by no means rare, and causes paralysis of the hind-legs and often pain. There is complete absence of pulse in the arteries. In dogs, thrombosis of the iliac and femoral arteries occurs occasionally. Euthanasia is nearly always necessary. (See also PARAPLEGIA.)
Aortic-iliac thrombosis is seen in the horse; the worm Strongylus vulgaris may be a cause.
Thrombosis of a blood vessel in the brain is a cause of apoplexy (in human medicine a stroke). (For thrombosis of the vena cava in cattle, see under VENA CAVA) (See also under ANTICOAGULANTS.)
A blood clot in a blood vessel or the heart.
Most animals used to living outside are usually unaffected by storms. The main exception is some horses which can become overanxious and excited. There is no complete answer to this, but it is probably best to keep the animals where they are most familiar. Horses used to being stabled should be placed in their familiar surroundings. Staying with them can also be helpful provided the person is calm. Some pets have problems, particularly dogs because of their exceptional hearing. If the owner knows that their animals are susceptible, they should be kept in a familiar place which is quiet and preferably relatively dark where they cannot cause damage or injure themselves. Sedatives can be used but it is better to try and accustom animals to the noises by means of specific CDs. (See also CHINESE LANTERNS; FIREWORKS; LIGHTNING STRIKE.)
One of the pyrimidine bases of DNA.
Situated in the anterior part of the chest cavity, and along the trachea in birds, this gland attains its largest size during early life and thereafter gradually dwindles in mammals as they mature. However, it is still prominent in adult rabbits. It has a role in immunity, as it removes young T-cells that happen to recognise the body’s own components as foreign. Failure of this function can result in auto-immune disease. (See T CELLS, which are thymus derived; also LEUKAEMIA.)
The thyroid cartilage is the largest cartilage of the larynx, and forms a well-marked prominence at the upper end of the trachea. It gives attachment to one end of each of the vocal folds, which are concerned in the production of voice. (See LARYNX.)
The surgical removal of all or part of the thyroid gland and undertaken in hyperthyroidism. (See under HYPERTHYROIDISM, THYROID GLAND, DISEASES OF.)
This is a very highly vascular ENDOCRINE GLAND, situated near the thyroid cartilage of the larynx. The gland usually consists of two lobes, one on either side of the larynx, joined by an isthmus in some species and individuals.
Located within or near the thyroid gland are the PARATHYROID GLANDS.
Minute structure Each lobe is enveloped in a thin capsule of fibrous tissue, strands from which pass into the organ, dividing it into lobules.
Function The most important hormone secreted by the thyroid gland is an iodine-containing compound called thyroxin. This increases the rate of metabolism, and is released when an animal is exposed to cold, for example. In hot weather, thyroid activity is reduced. Thyroxin is essential for growth and reproduction, and influences lactation.
Secretion of the hormone is controlled wholly or in part by a hormone from the anterior lobe of the pituitary gland. (See also PARATHYROID GLANDS.)
Enlargement of the thyroid gland is known as GOITRE. Goitre may occur when there is either too little or too much of the thyroid hormone, thyroxin, produced.
Dwarfism in young animals (cretinism) can result from failure of the gland to produce sufficient thyroxin.
Hypothyroidism An insufficiency of thyroxin is known as hypothyroidism, and may be associated with insufficiency of iodine in the diet (see GOITRE). The rate of metabolism is slowed, while there is an increase in body weight, loss of hair, and lethargy.
One form of hypothyroidism, MYXOEDEMA, affects the skin, causing its deterioration.
Treatment includes the use of thyroid extract; and iodides if appropriate.
Hyperthyroidism, or excess thyroxin in the blood, is characterised by loss of weight, sometimes an increase in appetite, polyuria, thirst, increased rate of metabolism and heartbeat. Enlargement of the gland may be detected on palpation. The animal may become restless or irritable. Protrusion of the eyeballs (exophthalmic goitre) may occur.
Hyperthyroidism is seen in elderly cats. They are mostly thin, and it is this loss of weight which causes the owner to seek veterinary advice in many instances. In addition to the signs mentioned above, diarrhoea may occur.
Treatment is surgical: removal of one gland, or ligation of the anterior arteries; alternatively, the use of drugs such as sodium fluoride or methylthiouracil.
Tumours of the gland include ADENOMA; sarcoma and carcinoma (see under CANCER), and EPITHELIOMA).
The chemical name is tetraiodothyroxine (T4); it is the active principle of the THYROID GLAND. It contains IODINE and is a derivative of the amino acid TYROSINE. It is used in pharmaceutical preparations to correct hypothyroidism, a common endocrine deficiency in dogs.
A MACROLIDE antibiotic active against Treponema hyodysenteriae (swine dysentery), various Gram-positive organisms, and Mycoplasma hyosinoviae (a cause of arthritis in pigs). It must not be used at the same time as MONENSIN SODIUM or SALINOMYCIN.
A semi-synthetic prostaglandin preparation used to induce parturition in sows. It should not be administered before the 111th day of pregnancy.
A small breed of dog in which LENS LUXATION and PROGRESSIVE RETINAL ATROPHY are inherited as recessive genes.
The tibia is the larger of the two bones which lie between the stifle and the hock. In animals which possess fewer than five digits in their hind-limbs, the tibia has become modified so that it sustains the greater part of the weight borne by the limb – the fibula, its complementary bone, having become reduced in size and importance. The tibia lies just below the skin on the inside of the limb, in such a position that it is liable to be injured by kicks, blows, etc., and in this connection is of more importance than those bones that are surrounded by massive muscles which afford some protection. It is not uncommon for the tibia to become fractured, but the parts remain held together by the very dense periosteum that covers the bone. In the smaller animals, the setting of the fractured bone is a routine. (See BONES; FRACTURES.)
Tibial dyschondroplasia A crippling deformity occurring in certain strains of chickens, ducks, and turkeys selected for high growth rates. It is due to a cartilage abnormality.