Diet And Nutrition

Feed represents the single largest expense in mink production, so the feeding program is crucial to a farm's profitability. Because of significant differences in the nutritional needs of mink from those of other domesticated animals, mink farmers have been unable to rely on information gathered for other species in developing diet formulations, and have had to do a lot of work for themselves.

As carnivores, mink require a diet derived primarily from animal sources, be they meat, fish, poultry, or dairy. Many mink farms base their feed programs on expired produce originally intended for humans, or on by-products collected from packing plants. The food producers also benefit because the amount of waste they must dispose of is reduced.

Diet formulations are dictated to a great extent by the length of the mink's digestive tract, the shortest of any domesticated species. Food can pass through a mink in as little as 2.5 hours, compared with about 72 hours for cattle, which means their diet must be highly digestible. The major nutritional needs of mink, like other species, are protein and energy, but the quantities and form in which they are ingested demand special attention.

A mink's protein needs are high because, in addition to providing for growth and maintenance of body tissues, it must also provide for fur production. Accordingly, proteins fed to mink should be of high biological value, supplying a good mix of the essential amino acids. Muscle tissues require considerable lysine and methionine, while fur production needs methionine, arginine, and cystine. Quality protein can be derived from eggs, fish and meat products, and dairy products such as cheese. Conventional mink diets contain such protein sources in a fresh state, often purchased in bulk and placed in cold storage until they are needed.

Most farm animals obtain their energy from carbohydrates, but mink use them to a much lesser extent, deriving most of their energy from dietary fats and oils. Such feedstuffs, however, must be stored correctly or they will

Fig. 2 The color and quality of a mink's pelt are good indicators of its health and diet. The pelt at left shows graying and banding of the fur, indicating the presence of avidin in the diet. The pelt at center has been parted to show a condition known as ''cotton fur,'' a deficiency in melanin formation absent in normal mink (right). (View this art in color at www.dekker.com.)

Fig. 2 The color and quality of a mink's pelt are good indicators of its health and diet. The pelt at left shows graying and banding of the fur, indicating the presence of avidin in the diet. The pelt at center has been parted to show a condition known as ''cotton fur,'' a deficiency in melanin formation absent in normal mink (right). (View this art in color at www.dekker.com.)

oxidize and turn rancid. Vegetable oils are not too problematic because they usually contain sufficient vitamin E, an antioxidant, to retard the onset of rancidity. Fish oils, however, are high in unsaturated fatty acids, which are easily oxidized, and lack the protective levels of vitamin E.

Supplementary minerals and vitamins can be supplied naturally as components of a mink's diet, or added in synthetic form. Minerals such as calcium and phosphorus, for example, can be derived either from bone-in products, such as whole fish, or by adding dicalcium phosphate to the feed. Most of the vitamin requirements, meanwhile, can be met by using so-called ''protective feeds.'' One of the most popular of these is liver, usually from beef cattle or chickens, and many farmers include liver in amounts of 5% or even 10% of the diet as a safety measure.

Mink farmers usually calculate dietary requirements for chemical nutrients based on the published works of animal nutritionists.[2,3] They then set about gathering appropriate raw materials at the best prices, often showing great ingenuity in formulating diets from a wide range of feeds and by-products. Sometimes farmers form feed cooperatives to achieve economies of scale, and take delivery every other day or so of however much feed they need.

In the quest for diet formulations that are both nutritious and economical, inevitably some diet-related problems have been identified in mink (Fig. 2). One example is ''cotton fur,'' a bleached-out and consequently worthless fur condition, which has been linked to the presence in the diet of a substance that interferes with iron metabolism. Found in some fish such as hake, this substance prevents the formation of melanin, a dark fur pigment. Another is ''fur graying'' caused by the presence in the diet of avidin, found particularly in turkey eggs, which creates a deficiency of the B vitamin biotin. The U.S. fur industry has formed the Mink Farmers' Research Foundation, which sponsors research to solve and advise on such problems.

In recent years, considerable effort has been expended on developing dry feeds for mink that meet the requirements for both growth and furring. The incentive here is to reduce the cold storage costs associated with fresh feed, and many farms now use dried, pelleted feeds at some time of the year.

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