Origin

The domestic ferret is often confused with the North American black-footed ferret, Mustela nigripes, which shows a striking physical similarity to Mustela eversmannii (the steppe polecat), so a short description of each will be provided to clarify the differences.

Domestic Ferret

According to one author, ferrets (M. putorius furo) have been domesticated for over 2000 years [3], but confusion exists because of the scarcity of written records, the use of different nomenclature in different regions, and translation difficulties from one language to another. Aristotle, in his early descriptions (ca. 350 bc), stated that there existed an animal, which may have been a ferret, that could become very mild and tame [3].

Early accounts in Greek and Roman literature from Strabo (ca. 63 bc– ad 24) and Pliny (ad 23–79) noted that ferrets were used for hunting rabbits. These earlier references to ferrets are probably the basis of the belief that ferrets originated in North Africa (Fig. 1.2) [3]. This belief has been questioned and a premise put forth that ferrets were first domesticated in countries of Southern Europe, bordering the Mediterranean [4]. Evidently, ferrets were bred specifically for rabbiting (rabbit hunting) and were muzzled before being sent into rabbit burrows. This practice was later introduced into Asia, and the British Isles, where the sport is still practiced today. The first illustration of ferrets used for rabbiting occurs in a fourteenth-century manuscript (Fig. 1.3) [3].

c1-fig-0002 — Fig. 1.2. The ferret. (Reprinted from Thomson APD (1951) A history of the ferret. J Hist Med 6: 471.)

c1-fig-0003 — Fig. 1.3. Ferreting in the Middle Ages, about 1300 ad. (Reprinted from Thomson APD (1951) A history of the ferret. J Hist Med 6: 471.)

In the Linnaean classification system, the ferret was named Mustela furo, and its identity has remained firmly established since then. The word “ferret” is derived from the Latin furonem and the Italian furone, meaning thief [3,5]. The word “putorius” is derived from the Latin putor, a stench, which applies to the musky odor of the ferret. Today, “ferret” is also used as a verb and connotes the ferret's behavior and traits: to remove from a hiding place, to search out with keenness, or to draw out by shrewd questioning.

The ferret (M. putorius furo) has been and is now used for hunting, biomedical research, and in North America and other countries as a pet, and is most likely a domesticated version of the wild European ferret or polecat (Mustela putorius or M. furo) [3,6]. Alternatively, it may be related to the steppe polecat (M. eversmannii), which it closely resembles in skull morphology [7]. The domesticated ferret, although introduced to North America by the early English settlers some 300 years ago, has not established feral colonies on this continent.

Behavioral differences between the domesticated ferret and the wild European polecat have been documented. The ferret is not as temperamental nor as vigorous and agile as the European polecat [6]. In addition, domesticated ferrets do not develop a fear of humans nor of unfamiliar environments, and are more tractable. The F₁ hybrids of the domesticated ferret and polecat, however, were found to develop a fear of humans when left with their mothers during a critical period between 7.5 and 8.5 weeks of age [8]. Imprinting may be involved in this process. When attention response to a rustling noise was tested, the wild ferrets and the F₁ hybrids habituated more rapidly than the domesticated ferret. The F₁ hybrids’ responses depended on their previous environmental history—animals raised outdoors responded differently from those raised indoors. Because the ferret's natural habitat contrasts greatly with the indoor environment, those ferrets raised indoors showed a greater response. These findings agree with Lorenz's hypothesis that the behavior of domesticated animals resembles that of juvenile individuals of their wild counterparts [9].

The wild ferret is completely interfertile with the European polecat, thus verifying their close genetic relationship. The wild European ferret, however, usually produces only one litter, while the domesticated ferret produces two or more litters yearly [10]. The female ferret and male stoat (Mustela erminae) will also produce fertile hybrids [11]. In addition, the F₁ generation of a wild polecat and domesticated ferret is fertile. The steppe polecat can also interbreed with black-footed ferrets [12]. The wild polecat, or ferret native to much of the British Isles and northern Europe, is also known as the fitch, fitchew, foul marten, fitchet, or foumart [5,6].

The Dutch were the first to visit New Zealand in 1642 but received an inhospitable welcome by the native Maoris who killed four of the explorers [13]. The islands weren't seen again by the Europeans for another 127 years when James Cook made three visits in 1769–1770, 1773–1774, and 1777. Whaling and sealing occupied the first settlers’ primary interests for the next several decades, followed by a period when settlers exploited abundant timber resources. In 1860, gold was discovered and resulted in an influx of tens of thousands, and in 1867, the West Coast reached a peak population of 29,000. Land-hungry colonists expanded acres of farming, and because of a lack of native game to shoot for food, began to import a variety of game animals. Wild rabbits were introduced in 1864 on the South island. By the 1870s, rabbits were creating serious economic loss as well as soil erosion on large tracts of farming land. Flocks of sheep were reduced drastically because of lack of natural grazing pasture. Even though millions of rabbits were killed in an effort to control their devastation on grazing land, there was only the slightest effect on reducing the rabbit population. Natural predators to control the rabbits in New Zealand were lacking, and the farmers therefore turned to importing a predator, the domesticated ferret, already renowned in Europe for its skills as a rabbit hunter. Strong objections were voiced by ornithologists and some of the acclimatization colonists in New Zealand who argued that ferrets, if introduced to control rabbits, would instead decimate the native bird population, especially the flightless birds. The farmers’ demands prevailed, and the first five ferrets were released in the Conway River valley in 1879. They were released by the thousands in 1882–1886 as were two other mustelids, stoats, and weasels. However, the debate about the merits of the introduction of these predators continued. For example, researchers predicted the consequences of these actions in 1885 in a presentation to the Auckland Institute: “… if stoats, ferrets, weasels … are turned out to destroy rabbits, it will be difficult to protect the birds, as these creatures destroy them, especially ground birds such as kiwis, kakapos, wrens … in Austria we destroy these animals at every opportunity. They are very cunning, and will not take poison while they can get live prey. Rabbits are much easier destroyed by shooting, netting, or bagging with ferrets when the land becomes more closely settled” [14].

The New Zealand Department of Agriculture bred ferrets for release until 1897, and private breeders continued until 1912, producing approximately 300 a year.

Despite this influx of mustelids, it soon became painfully obvious that the newly introduced predators were not having the desired dramatic effect on rabbit numbers. Instead, within 6 years, there was a drastic decline in native birds in the areas where the mustelids were released. On a positive note, however, the wild rat and mouse population did appear to be reduced. The government finally changed its policy in 1903 and amended the Rabbit Act by removing from the statute protection of the “natural enemies of the rabbit.” Instituting bounties on mustelids had little effect on their numbers and was abandoned in 1950. Even harvesting large numbers of ferrets and stoats for their fur in 1944–1948 made no apparent reduction in their numbers [15]. It wasn't until the 1950s when rabbits were controlled by chemical means that ferret numbers were significantly reduced [16]. The direct damage to native fauna attributed to the introduction of mustelids are on endangered bird species in New Zealand, particularly flightless birds. Of 18 separate bird populations now considered rare or endangered, 11 of these could have been affected by stoats and/or rats, in addition to other factors such as deforestation or other effects by human encroachment on native habitat. Interestingly, however, there is not a single known extinction or diminution of a bird species in New Zealand that can be solely or definitively attributed to any of the mustelids, despite all that has been written about their destructive predatory behavior. In a detailed survey conducted in 1973, the authors concluded, “It is actually difficult to attribute the decline of any native bird directly to mustelids” [17]. Likewise, throughout the recorded histories of bird species extinctions since 1600, on islands worldwide, only 1% of 163 extinctions were directly attributable to mustelids, compared with 26–54% attributed to cats and rats, respectively [18].

Interestingly, the Department of Natural Resources in Queensland, Australia, have declared pet ferrets illegal under the Rural Protection Act, 1985, stating that buying and selling pets can result in fines up to $60,000. In July 2003, the Rural Lands Protection Act was replaced with the Land protection (Pest and Stock Route Management) Act 2002 and Regulations 2003 and lists ferrets as a prohibited/declared Class 1 pest. A Class 1 Pest under the Act are animals which represent a threat to primary industries, natural resources, and the environment. Under the Act, it is an offense to introduce a ferret into Queensland, feed a ferret, release a ferret, or keep a ferret, unless issued with a permit to do so; permits to own ferrets are issued only to bona fide zoos and wildlife parks [19]. In a National Resources, Mines and Energy (NRME) correspondence, Mr. John English MP, Member for Redlands, wrote to Stephen Robertson MP, Minister for NRME, on behalf of the President of the Queensland Ferret Welfare Society, Barbara Cowell. The following reply was forwarded to Barbara from John English. “Thank you for your letter of 30 April 2004 making representation on behalf of Mrs Barbara Cowell of Macleay Island concerning the keeping of ferrets as pets in Queensland. Only zoos or wildlife parks are able to apply for a permit to keep ferrets in Queensland. There are no provisions in legislation for the keeping of ferrets as pets due to their pest potential. Ferrets are not native to Australia and have the potential to establish wild (feral) populations, as they have already done in New Zealand and the British Isles. In New Zealand, ferrets and stoats have become serious predators of native bird-life and their eggs, particularly ground-nesting birds. Ferrets are also known to be vectors for dangerous exotic diseases such as rabies. Although other states have failed to restrict the keeping of ferrets, they are taking a major risk by allowing these animals to be kept as pets. This concern is highlighted by a recent report of wild ferrets being seen in Tasmania. Also, ferrets established in Western Australia were controlled by trapping. Several states have banned the keeping of wild ferret breeds, known as polecats even though there is no reliable way of differentiating between wild and domestic breeds. Queensland, therefore, considers that it is sensible and important to prevent the keeping of this potential pest. I have noted the suggestion for regulation or licensing of keeping. Restricted keeping using permits was investigated for pet domestic rabbits and found to be prohibitively expensive. Section 274(3) of the Land Protection (Pest and Stock Route Management) Act 2002 provides the power for an authorised person to destroy or dispose of a seized pest if a permit for keeping is not produced within 48 hours. An authorised officer cannot dispose of a seized ferret by handing it to someone to transport to New South Wales because a permit cannot be issued to the person transporting the animal. The authorised officer would need to drive to the border with the animal and it is not appropriate for an officer of my Department to spend time doing this” [19]. The agency still claims that ferrets have pest potential and are a threat to native wildlife, especially small native mammals and ground dwelling and nesting birds.

In addition, the state of Washington had listed the ferret (M. putorius) as a feral animal on San Juan Island, where it was initially introduced together with other predators to control an excessive population of European rabbits. Because of the competition, the population of native mink (Mustela vison) on the island has been reduced in number [20,21]. However, in a letter dated April 14, 1988 from the Nongame Program Manager of the Department of Wildlife in Washington State, Mr. Juelson states to Bill Philips of the California Domestic Ferret Association regarding the alleged ferret colony on San Juan Island, “I am prepared to state that, to the best of my knowledge, there are no ferrets living in Washington that prey upon native wildlife. Those rabbit populations dramatically decreased a few years ago and I have been unable to find anyone who has observed a ferret there since.” In addition Mr. Phillips surveyed all 50 states and received a reply, in writing, to the effect that no feral colonies of the domestic ferret were known to exist anywhere in the United States. Some officials suggested that sightings of ferrets could either be the result of escaped pets and strays or mistaken identity with the long-tailed weasel (Mustela frenata).

Morphology

The ferret has a long body, with short muscular legs and a long tail. The adult ferret's average body length is 44–46 cm from the nose to the tip of the tail. Some of its anatomic features resemble those of the cat and dog—the anterior and lateral portions of its skull resembles that of a cat, not a dog. On the other hand, the zygomatic bones of the eye orbits of the ferret and dog are open, while those of a cat are almost closed [22].

As a result of its behavioral traits and burrowing instincts, the ferret has developed certain anatomic adaptations. It is postulated that, because of its burrowing nature, the ferret's long neck and placement of the carotid arteries may help the ferret maintain sufficient cerebral blood flow when it turns its head in tight confined spaces (see Chapter 2) [23]. The compliant chest wall, total lung capacity, and respiratory reserve, which is very large in comparison to body size, are anatomic adaptations. The relatively large-diameter airway and long trachea result in a lower central airway and pulmonary resistances in comparison to those of other animals of similar size (see Chapter 4) [24]. It is important to note that the airways of the ferret grow in length and diameter in proportion to body length [25]. Similar findings have been recorded in humans [26].

The ferret's short digestive tract is characteristic of other carnivores, but a cecum and appendix are absent in this species. Also, the large intestine is unique, because there is no external anatomic division between the ileum and the colon, and thus the lower intestine appears grossly as one long, undifferentiated organ [27]. Anatomy is discussed in greater detail elsewhere (see Chapter 2).

Coat Colors

The genetics of coat colors has been described and is based largely on studies conducted by Fara Shimbo [28,29]. These genetic coat color traits have been highlighted in the text by John Lewington [30]. However, it is important to note that unless the important characteristics, such as pigmentation of both guard coat and under coat, as well as skin pigment and markings, are carefully documented, it may never be possible to fully characterize the genetics of coat colors of ferrets [31]. Having large numbers of ferrets for extensive breeding trials over many generations will be required to achieve these goals.

Readily available commercial stocks, based on coat color, are albino (English; Fig. 1.4), sable or fitch (black guard hair; Fig. 1.5), Siamese (brown guard hair; Fig. 1.6), silver mitt (sable with white chest and feet; Fig. 1.7), and Siamese-silver mitt (Siamese with white chest and feet) [32]. The fitch or so-called wild coat color is the most common coat color, recognized by yellow-buff fur with patches of black or dark brown, particularly on the tail and limbs [33]. The facial fur is somewhat lighter, with a dark mask over the eyes that is less marked in neutered or immature animals. The eyes are usually dark brown.

c1-fig-0004 — Fig. 1.4. Albino (English) ferret.

c1-fig-0005 — Fig. 1.5. Sable or fitch ferret (black guard hair).

c1-fig-0006 — Fig. 1.6. Siamese ferret (brown guard hair).

c1-fig-0007 — Fig. 1.7. Silver mitt ferret (sable with white chest and feet).

The albino (with a nonpigmented iris) is also seen frequently, but this coat color is recessive to the pigmented wild phenotype. The pet industry is currently promoting additional coat colors. Varieties of Siamese are chocolate (dark brown), cinnamon (reddish brown), and butterscotch (very light tan) [34]. Other mutations have produced a wide selection of coat colors and patterns. Black-eyed whites are born white and remain pure white and have dark eyes. Ferrets of any body color with white paws are known as mitts. Predominantly dark-colored young ferrets with white feet and some white in their coats are called silver mitts. A young silver ferret usually has some white hair in the mask, making it indistinct, and often has ventral patches of white, commonly including a spot on each stifle. With every molt, more white appears throughout the coat, until the ferret is almost pure white. Different markings have become common in ferrets. Some have white toes on one or more feet, or spots or rings of white on their tails. Ferrets that have white heads and bibs are known as pandas. A blaze, or a single streak of white in the center of the head above the mask, is another pattern found. Panda or blaze markings appear to be dominant phenotypes and can be superimposed on any coat color. More recent mutations have resulted in pastel- or champagne-colored ferrets, which are solid pale beige with no masks, and angoras, which have much longer, fuzzier coats than usual. Ferrets carrying the genes that usually produce silver mitts also produce occasional black-eyed whites or odd-colored kits [30]. Mating silver mitts or black-eyed whites with each other can result in severe congenital abnormalities in the offspring, fetal resorption, or abortion. Congenital abnormalities are not commonly associated with other common coat colors.

North American Black-Footed Ferret

The black-footed ferret, M. nigripes, the North American representative of the Holarctic group of polecat species, probably made its first appearance in North America about 100,000 years ago (Fig. 1.8). It is closely related to M. eversmannii, the steppe polecat, which unlike the black-footed ferret, utilizes several sources of food. Although suggested to be conspecific, morphological comparisons [35] and more recent molecular studies [36] indicate that M. nigripes and M. eversmannii are indeed separate species. It was at one time prevalent on the North American plains where its main prey, the prairie dog, lived in large colonies called “prairie dog towns” [37]. Consequently, in the first half of the twentieth century, large-scale prairie dog eradication programs resulted in placement of the black-footed ferret on the endangered species list in 1967.

c1-fig-0008 — Fig. 1.8. Black-footed ferret: endangered species in North America.

In the 1960s and 1970s, researchers attempted to breed the animal in captivity and to understand its biology and diseases. These attempts were basically unsuccessful, and the programs were abandoned [38].

The species had last been sighted in South Dakota in the early 1970s, and by 1980, many believed that the black-footed ferret was extinct [39]. In 1981, however, a rancher's dog killed a weasel-like creature near Meeteese, Wyoming. Luckily, the animal was retrieved by the rancher's wife, and a local taxidermist recognized it as a black-footed ferret [39]. Biologists from the Department of Fish and Wildlife Service and from the Biota Research and Consulting Company soon converged on the area and documented new sightings of the black-footed ferret. Because they are nocturnal and spend most of their time in underground burrows, they are difficult to track. The 80,000-acre area of prairie dog colonies was surveyed, and it was estimated that there was a population of 60 ferrets for the summer of 1982, 88 in 1983, and 128 in 1984 [37].

Recent studies indicate that ferrets hunt over a 100-acre area, which is a large range for a small mammal. Therefore, only large prairie dog complexes (several thousand acres), made of many closely spaced prairie dog colonies, can support a successful breeding population of 100–200 black-footed ferrets [40]. Importantly, field tests are ongoing to evaluate a new vaccine developed by the National Wildlife Health Center to protect prairie dogs against sylvatic plague [41]. In the summer of 1985, the increasing black-footed population underwent a dramatic reversal. The first count, in August of 1985, estimated a dramatic decrease—only 58 ferrets. This number declined to 31 in October of the same year. Canine distemper, often reported in wild carnivores, had been introduced into the colony and, of the 12 ferrets brought into captivity, 6 died of the disease.

Even though previously attempts to breed black-footed ferrets were made and surviving offspring of captive black-footed ferrets were not successfully produced, a decision was made in 1986 to capture the 18 known living wild-born ferrets. This was done on the basis of detailed analysis which indicated that the risk of extinction of the only known population of wild black-footed ferrets was greater than the risks of capture and establishing a breeding colony in captivity [42].

A captive breeding program was then established at Sybille, Wyoming, under the direction of Dr. Tom Thorne, a wildlife veterinarian [43]. These efforts have been successful, and litters of black-footed ferrets have been produced in captivity since the summer of 1987. In establishing this captive population, every effort has been made to retain the maximum amount of genetic diversity that was present in founder ferrets captured in 1986. By 1991, there were about 325 black-footed ferrets in captivity. Breeding colonies have also been established at six different zoos throughout the United States. Six black-footed ferret reintroduction sites have been established in South Dakota in an ongoing attempt to reestablish wild black-footed ferret colonies [44]. For a complete discussion of the remarkable collaborative efforts of individuals and agencies to save the black-footed ferret from extinction, see Chapter 10.

Uses

Rodent Exterminators

In England and the United States, domestic ferrets have been used for rodent control. This practice became popular in the United States during the early part of the twentieth century, and tens of thousands of ferrets were raised and sold for this purpose. The Department of Agriculture distributed bulletins announcing the use of ferrets for rodent abatement [45]. Because rodents have an extreme fear of ferrets and will flee even from their scent, only a few ferrets were needed to disperse literally hundreds of rodents from granaries, barns, and warehouses.

A ferretmeister would deploy his ferrets on an infested farm or granary, and the animals would then “ferret out” the rodents from their hiding places and nests. Men and terrier dogs, strategically located, would eradicate the rodents as they emerged from hiding. Alternatively, small farms or granaries would maintain ferrets and allow them territorial imperative for up to about 650 ft (200 m)—considered to be the ranging domain of a ferret with an adequate food source. The introduction of commercially available rodenticides, however, has dramatically reduced the popularity of ferrets as rodent exterminators.

Helping Control the Black Death

The houses were filled with dead bodies and the streets with funerals; neither age or sex was exempt; slaves and plebians were suddenly taken off amidst the lamentations of their wives and children, who, while they assisted the sick and mourned the dead, were seized with disease and, perishing, were burned on the same funeral pyre. To the knights and senators, the disease was less mortal though these also suffered in the common calamity. [46]

This graphic account of the dreaded disease, the bubonic plague, was recorded in Imperial Rome in the Second Century ad. This pestilence occurred again and again during the ensuing centuries. By the fourteenth century, the disease appeared in the Far East, spread to Asia Minor, and followed the trade routes to Europe. It did not make its arrival in the United States until 1900 when the disease appeared in California where it still exists enzootically in the ground squirrel and chipmunk. Although today the association with plague and rats seems obvious, it was not until the bacillus, Yersinia pestis, was isolated and cultured, could this causal relationship be definitively proven. After discovery of the infectious nature of the disease, it was soon established that epidemics among human populations closely coincided with epizootics of the disease in rats, particularly Rattus rattus. It still was not apparent how the two diseases in the two hosts were linked. The hypothesis first conceived by P.L. Simond of Spain that the plague bacillus was transmitted by the rat flea, though first discounted, was later proven to be correct [46].

With the life cycle and transmission of Y. pestis closely linked to rats and their fleas, tremendous efforts were mounted to eradicate the rat host and its flea, Pulex cheopis. For example, in Manila, Philippines, rat catcher groups of 300 men were assigned the formidable task of eliminating the omnipotent pest [46]. When rats were encountered, they were killed immediately. Some of these workforces had fox terriers imported especially from Australia, because of their agility and quickness. Others utilized trained ferrets which responded to their masters’ trained calls, like dogs. The ferrets were even more effective than dogs in killing rats. The ferret would grasp the rats in its jaws, and the ferret's teeth would then sever the rat's spinal column [46]. Undoubtedly, ferrets served a similar role in differing locales throughout the world to control rat infestations and hence reduce the likelihood of further spread of the dreaded pestilence. Though not discussed by Heister, the apparent resistance of ferrets to Y. pestis may have added to their value in highly infected areas where plague was enzootic in the rat population.

When hunting rats in plague-infested areas, one author recommended that each rat, as soon as it was killed, was to be submerged in a germicidial solution [47]. The sack containing these dead rats was treated in a similar manner. It was strongly urged that rats in plague areas be incinerated as well as the bag containing the rats. Even though attention was given to treating rat bite wound infection in ferrets, no discussions on ferrets becoming infected with the plague bacillus were found. However, it is now recognized that black-footed ferrets are susceptible to Y. pestis infection (see Chapter 21).

Historically, ferrets also have been used to control rodent populations on ships. The Massachusetts Colonial Navy, the state's Revolutionary War naval militia, was organized on December 29, 1775. By an act of the Commonwealth of Massachusetts state legislature, the present unit was reactivated in 1967 to carry on the tradition of the original Revolutionary War units. At an impressive naval ceremony held at Bristol Community College on September 14, 1986, the ferret was officially proclaimed the mascot of the Colonial Navy of Massachusetts. The following is an excerpt from the ceremony:

Today marks a milestone in the history of the Colonial Navy of Massachusetts. It gives me great pleasure to have all of you present here today, to bear witness to a unique naval ceremony, that to the very best of my knowledge, probably has not been performed since the late seventeen hundreds … over two hundred years ago. This was a traditional ceremony that both officers and men looked forward to with great delight. No … this was not a solemn change of command, nor an impressive commissioning of a new ship of the fleet … this joyous occasion was the “Introduction of the Ship's Mascot!”

Now in the days of the wooden men o’ war there was, quite often, an uninvited population of rodents aboard ship. They were certainly a nuisance and caused many a moment of unpleasantness among the crew. Dogs were completely unsuccessful mousers and besides, their barking kept both captain and crew awake. Cats were infinitely preferred over dogs, but they were unable to chase mice into the many narrow holes and passageways aboard the ship, so more mice escaped than were caught. But … there was one animal the rats and mice could never escape from … no matter where they tried to hide … no matter how small a hole they ran into … they were doomed! This animal could find them … anywhere! This animal was one of man's best friends and totally fearless. They were in great demand aboard the ships of the colonial navy, and fortunate indeed were the crews that had a ferret for a mascot and friend.

It is with great honor … that today … the Colonial Navy of Massachusetts hereby tenders the following proclamation:

Let it be known … that all men here and present bear witness. …

Whereas … on this day of our Lord … the fourteenth day of September, in the year nineteen hundred and eighty-six. …

Whereas … it has been common knowledge for centuries, that you possess the unique ability to ferret out and destroy … all manner of mice, rats, and rodents. …

And whereas, by these deeds, you have infinitely improved the quality of life aboard ship. …

And further whereas, by your kindness, gentleness and devotion to the shipmates you so dutifully serve. …

It is with the utmost gratitude and pleasure … that the Colonial Navy of Massachusetts, does hereby and forthwith, and by the unanimous proclamation of both officers and men … hereby proclaim Mustela furo, the ferret, as its official mascot [48].

Pet Ferrets and Their Status

The domestic ferret is becoming increasingly popular in North America as a pet. In 1980, according to a major ferret producer, about 12,000 ferrets were sold, approximately 50% for research and the remainder for distribution as pets [54]. Small commercial breeders are now advertising locally or in ferret newsletters and, in addition, two large commercial operations produced and distributed around 30,000 ferrets for the pet industry in 1986. One estimate states that 50,000–75,000 ferrets were produced in 1986 for use as pets in the United States [20]. In 1986, there were an estimated 400,000 ferret owners and 1,000,000 pet ferrets in the United States [20]. The International Ferret Association 1986 membership was 100,000, compared with 14,000 in 1981 [55]. In 1990, it was estimated that more than 7 million ferrets were kept as pets in the Unites States [56]. Currently, it has been estimated that there are 5 million ferrets as household pets in the United States, the United Kingdom has more than 100,000, Germany 115,000, Italy 105,000, and France 300,000 pet ferrets [57].

The categorization of the ferret historically as a wild animal is slowly disappearing. Indeed, the pet industry is promoting ferrets in lay and trade journals. Manuals are also extolling the virtues of the ferret as a household pet as well as providing helpful nutritional, husbandry, and preventative medicine information for the pet owner [34,58]. However, even now, some states, such as New York, historically required a special permit to own ferrets. In California and Hawaii, ferrets still may not be owned as pets. A historical reason often cited by opponents of ferrets as pets is the lack of a United States Department of Agriculture (USDA)-approved rabies vaccine for ferrets, and the number of documented cases of rabies in ferrets in the United States [54]. This argument has been partially muted by the availability of a USDA-approved rabies vaccine for ferrets. However, in some states, ferrets can still be legally seized and euthanized to screen for rabies if the ferret has bitten an individual (see Chapter 9).

Though the Humane Society of the United States was reported to have previously been in the process of drafting legislation to be submitted to 46 states, proposing that pet ferrets be banned as pets, this has not happened. Instead, the Humane Society of the United States recommends that if a household acquires a pet ferret, similar to recommendations for other companion animals, it should not be bred for commercial purposes. It also recommends that ferrets should not be purchased, but rather the prospective owner should acquire the ferret from a shelter [59]. There are a limited number of often-cited cases in which ferrets have attacked babies or young children, inflicting serious wounds [60–63] (Table 1.2). Although there are no data available with regard to why ferrets occasionally attack infants, case reports describe this behavior as unpredictable. Because of these attacks, one local ordinance, in Carson City, Nevada, has prohibited the sale of ferrets to households that have children under the age of 3 years. Unfortunately, no available surveys are published that compare the rate of ferret attacks with those of other pet animals [64].

Table 1.2. A Review of the Literature on Injuries by Pet Ferrets

The banning of ferrets as pets has been challenged in various states by organized lobbyists, efforts that are backed primarily by ferret owners and enthusiasts. For example, in Pennsylvania, lobbying efforts at the state legislature have been successful. The state, which once required licenses from the Game Commission for ferret ownership, no longer requires such licensure, and the ferret is now categorized as a domestic animal [34]. In Alaska, which had permitted pet ferrets, the Alaska Game Commission issued regulations banning pet ferrets, a ruling that was subsequently challenged and reversed by a pet owner. Based on scientific information, the court ruled that the ferret was considered a domestic animal, and the ferret was removed from the jurisdiction of wildlife regulations [34]. Legislative victories for pet ownership of ferrets in which restrictions have been lifted have also occurred in West Virginia, Maine, New Hampshire, and Massachusetts.

Previously, the American Veterinary Medical Association (AVMA) Council on Public Health and Regulatory Veterinary Medicine formally discouraged the ownership of pet ferrets [65]. This announcement created considerable controversy in the veterinary profession—in regard to whether ferrets are considered wild or exotic animals, as the Council on Public Health and Regulatory Veterinary Medicine maintains—especially in the area of rabies control. The association strongly opposes the use of wild or exotic animals as pets. Ferret breeders and owners, and some veterinarians who treat pet ferrets, argue that ferrets have been domesticated for over 2000 years and should not be considered as wild or exotic pets [66]. Currently, the AVMA, under the heading of exotic animals and wildlife, has formally addressed ferrets as pets or for use in research. The AVMA recognizes that ferrets are being kept as pets and for research purposes, and in those states or areas where ferret ownership is legal, the AVMA recommends the following: “Responsible ferret ownership: This includes knowledge pertaining to ferret husbandry (care, nutrition, housing, and species’ habits). It is also recommended that no ferret be left unattended with any individual incapable of removing himself or herself from the ferret” (see Table 1.2) and “Proper veterinary care by a veterinarian legally authorized to practice veterinary medicine: This includes preventive medicine and, when needed, medical or surgical care including spaying, castration, and descenting. Ferrets should be vaccinated against rabies, canine distemper and other diseases for which a licensed vaccine exists for use in ferrets” [67].

Biomedical Research

The ferret, although domesticated for hundreds of years, was not recognized as having potential as an animal model for biomedical research until the 1900s. Early studies utilized the ferret in classic experiments with influenza virus pathogenesis [69]. Today, the ferret is still the model of choice for studying the influenza virus, as well as other viral diseases (see Chapter 20) (Fig. 1.10). Two decades later, an article detailing the use of ferrets in research cited only 26 publications [69]. Even in the 1950s and early 1960s, texts compiling data on 60 to 90 mammalian species cited the ferret infrequently. For example, in the 1956 edition of the Handbook of Biological Data, reference was made to the ferret only 11 times, and it was not cited at all in the Biological Handbook: Blood and Other Body Fluids, published in 1961 [9].

c1-fig-0010 — Fig. 1.10. Dr. John Gorham, a pioneer in the use of ferrets in virology research.

Literature reviews undertaken in 1967, 1969, 1973, and 1985, however, reveal an increasing appreciation for the ferret's usefulness and versatility in the study of human physiologic, anatomic, and disease mechanisms [9,70–72]. In a review of research publications involving ferrets (1977–1984) using the BIOSIS database, citations were obtained from both Biological Abstracts and Biological Abstracts/RRM [70]. In addition to 8000 journals, BIOSIS covers symposia, reviews, preliminary reports, selected institutional and government documents, and research notes. MEDLINE, from the National Library of Medicine, was also used in the literature review, and over 569 citations were identified [70]. Of the articles cited, 27% (155) involved the use of the ferret in physiology, 24% of the citations were in virology and immunology, 10.4% in pharmacology, 8.4% in toxicology, and 4% in teratology. This compendium was published as part of an entire issue of the journal, Laboratory Animal Science, devoted to the use of the ferret in biomedical research [70]. In addition, scientific symposia centered around the ferret attest to their increasing popularity for use in biomedical research [73,74].

In 1991, a bibliography containing “selected” literature citations on the ferret and its use in biomedical research was published [75]. This bibliography was produced jointly by the Animal Welfare Information Center of the National Agricultural Library (NAL) of the USDA and the Division of Comparative Medicine at the Massachusetts Institute of Technology (MIT). Dr. James Fox, with the assistance of Marian Walke of MIT, contributed a large portion of the information from his own collection of ferret literature. NAL provided additional citations via extensive database searching. Databases searched include AGRICOLA, MEDLINE, BIOSIS, Life Sciences, and Zoological Record. Topics include ferret physiology, care and handling, and use in biomedical research. The document is designed to serve as a reference tool for individuals involved in the care or use of ferrets in the laboratory setting. While not comprehensive, the document provides extensive coverage of ferret biology, diseases, and use as an animal model. This document is organized by subject headings which include Anatomy/Physiology, Behavior, Techniques, Anesthesia/Surgery, Diseases, and Animal Models. Citations, which total 715, within the subject headings are arranged in reverse chronological order (based on publication date). When available, the NAL call number is provided for the materials located at the National Agricultural Library. An author index is provided at the end of the document.

The ferret's increasing popularity in research and as a pet is mainly a result of large-scale commercial production. For example, Marshall Farms, in New York, has been raising ferrets commercially for over 70 years (Fig. 1.11). Biomedical researchers in the United States can request a specific sex, weight, and age of the animal for individual experiments. Even though the ferret is nonstandardized in regard to an exact genotype and pedigree, its routine availability in a clinically healthy state has aided immeasurably toward gaining acceptance as a research animal. However, because many of these ferrets are bred by large commercial operations, concern has been expressed that unintentional inbreeding of these animals has made the ferrets more susceptible to diseases, for example, endocrine-related disorders.

c1-fig-0011 — Fig. 1.11. Mr. Gilman Marshall, a pioneer in the commercial rearing of ferrets for use in biomedical research. (Permission courtesy of Marshall Farms Group, Ltd.)

The domesticated ferret has and continues to be used extensively in studies involving virology, reproductive physiology, anatomy, and endocrinology, as well as in other areas of biomedical research. Because of the similarity of many anatomic, metabolic, and physiologic features to those of humans, use of the ferret is also being promoted as an alternative to the use of dogs and nonhuman primates in toxicology studies. A historic event regarding the use of ferrets in toxicology research was their introduction into the field of experimental teratology. This began with reports of their response to rubella virus and to chlorcyclizine, which produced cleft palates. Other substances that produce malformations in ferrets include β-aminopropionitrile, thalidomide, mustine hydrochloride, trypan blue, salicylates, and methylazoxymethanol acetate (MAM Ac). The use of MAM Ac has introduced the ferret to behavioral teratologists because it produces lissencephaly, a condition in which failure of development of cerebral gyri results in a nonconvoluted brain (similar to that of the rodent) [76]. The ferret is also being used to replace the cat in neuroendocrinology, neuroanatomy, and cardiology experiments (see Section III: Research and Applications). The recent completion of the ferret genome will undoubtedly increase the usefulness of this species in biomedical research (http://www.broadinstitute.org/scientific-community/science/projects/mammals-models/ferret-genome-project). Similarly, the recent successes of developing transgenic ferrets will substantially increase their use in biomedical research (see Chapter 28).

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1
Taxonomy, History, and Use

Taxonomy