Genetics And Breeding

The first domesticated mink were developed from wild animals caught in northerly parts of North America. These were dark brown to black in color, with a lighter underfur. Through selective breeding on farms, the coats have darkened to the point that today's so-called standard mink are almost jet-black.

From time to time, strikingly different pelt colors caused by genetic mutations are found among litters of newborn kits, and farmers may select them for further breeding. As a result, today's mink population includes a variety of exotic color phases such as silver-blue, ''sapphire'' (a very light bluish-gray), ''pastel'' (a brown color phase), and albino (white).[1] Breeding such phases can be difficult, however, and farmers often refer to studies on mink heredity by such experts as Dr. Richard Shackelford of the University of Wisconsin/Madison to increase their chances of success.

As with any livestock operation, a key to success is the selection of breeding stock. The process begins with close examination of the latest kit crop. Each animal is ranked according to a grading system, and the rankings are stored on computer. The farmer then decides how many of each sex he or she needs for breeding and selects these based on their rankings.

Color is an important criterion in selecting breeders, but other traits are considered too, such as size, vitality,

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Fig. 1 Modern mink farms raise their animals in clean, airy, and well lit sheds. (View this art in color at www.dekker.com.)

number of kits per litter, and freedom from disease. To speed up selection, farmers sometimes start by concentrating on one trait, such as color, before proceeding to the next. Many farmers also use what is called the index method to aid selection. This allows them to combine several traits, perhaps with different weightings, into a single index figure that is then used to rank the animals.

In early spring, cages are fitted with nest boxes filled with warm bedding such as shredded paper or grass straw, and breeding cards, containing information from the selection process, are hung over the cages. Prior to mating, males and females are often kept in separate parts of the shed, and females are generally restricted in their feed for a few weeks to keep them in active condition.

The males are then introduced to their chosen mates, with a mature male typically servicing 5 10 females and a kit male servicing 4 5. It is particularly important to ensure the males are fertile, and this may be done by extracting fluid from a female's vagina right after mating and examining it to determine the number of live, active sperm.

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