Nutrition of Fur Animals

NUTRITION OF FUR ANIMALS by Charles E. Kellogg ^ SILVER FOXES, minks, and rabbits are now being raised as part-time enterprises on a considerable number of farms, and some producers are in the business on a large scale. There is also some interest in the raising of martens and fishers. Here is a summary of the scientific work—not yet very extensive—that has been done on the feeding of of these animals, with special emphasis on its practical application. THE ONLY FUR ANIMALS that are now being raised commercially to any great extent are silver foxes and minks. Martens and fishers also have commercial possibilities if satisfactory reproduction can be obtained in captivity. Attempts have been made at one time or -another, largely through the efforts of propagandists, to ''ranch-raise'' skunks, badgers, raccoons, beavers, and muskrats for their fur, but the undertakings were not profitable because the cost of feeding and other costs of production exceeded the market quotations on similar wild-caught skins. A striking mutation may develop in some of these species, however, which will produce an animal with new^ characteristics that will make production in captivity remunerative. Natural selection in the wild, where matings are promiscuous, fosters the survival of those animals best fitted to live under rigorous conditions. The survival of fur animals in captivity, where matings can be controlled, is dependent upon their ability^ to produce beautiful pelts economically under more or less pampered conditions, rather than upon adaptation to rigorous competitive living. The profitable t^^pe is the docile, tractable, easily kept animal that responds to care without putting on excess fat and becoming sluggish and nonproduc- tive. Economy of handling in captivity does not permit the retention of animals that require considerable exercise to be prolific. Elimina- tion of the undesirable types is taking place on the more progressive ranches, though most emphasis in selection has thus far been placed on color and density of fur, prolificacy, and other factors that have a greater immediate bearing on commercial value. ' Charles E. Kellogg is Biologist, Section of Fur Eesources, Division of Wildlife Eesearch. Bureau of Bio- logical Survey, which was transferred to the Department of the Interior July 1,1939. 871 872 YEARBOOK OF AGRICULTURE, 1939 The abundant available information on human and domestic- livestock nutrition provides some foundation on which to develop suitable rations for fur animals in captivity. But after all, foxes, minks, martens, and fishers are carnivorous animals recently taken from the wild, and much remains to be learned about their food requirements. This fact has caused governmental authorities in this and other countries to establish experimental units for specific research on the nutrition of fur animals that give promise of profitable commercial production. RESEARCH ON FUR ANIMALS LIMITED Though numerous experiment stations in the United States are studying the nutrition of domestic livestock,^ only one Federal experiment station, three State agricultural experiment stations (Oregon, Wisconsin, New York (Cornell)), and one Territorial station, are doing nutritional research work with fur animals. The studies at all the State stations were started within the past 2 years, and those at the Territorial station, at Juneau, Alaska, were initiated in the fall of 1938. Cornell University conducted a metabolism study with minks for 1 year (1936), and in the fall of 1938 began research work on the nutritive requirements for growth, fur production, and reproduction of foxes and minks in cooperation with the Bureau of Biological Survey. The United States Fur Animal Experiment Station at Saratoga Springs, N. Y., had been located from 1916 to 1923 at Keeseville, N. Y. Small numbers of silver, red, cross, and blue foxes, martens, minks, fishers, badgers, skunks, and domestic rabbits have been maintained at this station at different times. All species were eliminated by 1938 except silver foxes, minks, and martens. Testing various types of equipment, pens, and kennels, checking trial feed formulas, and perfecting methods of handling and management were essential in the earlier years before controlled experimental work could be in- augurated. Satisfactory control of fur-animal diseases and parasitic infestations also had to be established. All of these studies provided fundamental information of distinct value to fur farming. SILVER FOXES CHARACTERISTICS AND BREEDING HABITS The beauty of the silver fox fur is partly due to the fact that foxes have tw^o types of hair—fine underfur and longer, coarser top hair called guard hair. Many of the guard hairs have white bands of vary- ing widths toward the tips; these hairs are not entirely white or even white-tipped, as is commonly supposed. The silver-black fox is a mutation of the red fox in which the black pigment has replaced the red. The white bands appear silver on the black background. The degree of silver is determined by the width of the white band and the frequency of these banded hairs over the entire body of the fox. The present popular bright silver pelts have wide bands of clear white on most of the guard hairs over the entire body except the neck region. The black tips of the guard hair overlying or veiling the clear white band accentuate the silvery appearance. The clearness NUTRITION OF FUR ANIMALS 873 of the colors, though largely due to selective breeding, is affected by feeds and by systems of management. The mutations to black occur in wild red foxes in Alaska as well as in the eastern part of Canada. The silver fox developed from the eastern strain, most common on farms at the present time, is known as the eastern standard type. The average weight of males of this type at maturity is 12 to 15 pounds and that of the females 10 to 12 pounds, when in good thrifty condition. Matings occur from middle January to middle March. Pair-mating 1 male, technically known as a dog, and 1 female, or vixen, in the same pen is followed by the larger ranchers. Recenth^ some of the small ranchers have been mating their foxes polygamously, that is, using 1 dog to breed as many as 10 vixens. Not more than one litter is produced each year after a gestation period of 52 days. A few litters of 9 or 10 are obtained, but an average production of S% to 4 young for every vixen is considered satisfactory, and of course some of the vixens do not produce each year. Though the ranchers with large numbers of animals leave the pups with the parents until September, others wean them at about 8 weeks old, when they weigh about 4 pounds, male pups being about a quarter of a pound heavier than females at this time. Smith (1067, p. S6Y found the body length of male pups to be 16}4 inches at this age and that of females lb){ inches. The young foxes attain the weight of mature animals when about 7 months old. The pelts are taken in November or December when the animal is 9 to 10 months old, depending on climatic conditions. Fox pups will breed the following spring when they are about 1 year old. The mature animals begin shedding their fur the early part of June. Shedding is usually complete by August, depending on climatic conditions and general health of the animal. A full growth of new fur must develop by pelting time in early winter. Though it is generally believed that pups shed their fur the process is quite gradual. Foxes are productive until 9 to 10 years of age but they are seldom kept that long. At present the higher prices prevailing for pale silver skins are inducing fox breeders to replace the darker mature breeding animals with lighter-silvered pups. MANAGEMENT PRACTICES At the larger ranches the breeding pairs of foxes are still provided with ground-floor pens 20 by 40 feet to about 40 feet square with a 2-foot wire overhang to prevent escape. At other ranches the males and females are maintained in separate pens with raised wire floors (fig. Î, C), for sanitation and control of parasites, 6 to 8 feet wide and rang- ing from 16 to 30 feet long and 4 to 6 feet high. A wire netting covers the top of this entire pen. The specialized larger ranches about October 1 transfer the animals to be pelted into ^'furring runs" (fig. I, A). A furring run may be a fenced area of 25 acres of dense woods, which is sufficiently large for about 500 animals. Usually no shelter is provided. Other fox farmers have built raised wire-floored furring sheds large enough for confining 50 to 100 foxes during the day; these animals ma\^ be released during the night into a large fenced outdoor runway. ^' Italic numbers in parentheses refer to Literature Cited, p. 1075. 874 ' YEARBOOK OF AGRICULTURE, 1939 On other farms the sheds are divided into compartments for 2 to 4 animals each. Protecting the foxes from sunHght tends to produce clearer-colored pelts free from a rusty or tinged appearance. The largest ranches have as many as 8,000 vixens and employ a large crew of men. Smaller enterprises may have as few as half a dozen vixens being taken care of at odd moments. The majority of the fox farms in the United States are part-time enterprises. Feeds and Feeding Practices Though foxes in the wild are largely carnivorous they do eat berries and other fruits, some vegetation, the contents of the digestive tracts of rodents, and occasionally insects. When foxes were first confined, there was considerable difficulty in feeding them properly.

Load more