Genetic Diseases

By Horst W. Leipold.

Mulefoot (syndactyly) in a Holstein calf Notice right front foot (a) is affected with syndactyly while the left front foot (b) is normal.

Congenital defects or diseases are abnormalities of structure or function present at birth. In cattle many of these defects of either genetic, environmental, or unknown cause or due to environmental-genetic interaction have been identified. The genetically caused diseases are mostly due to homozygosity of a simple autosomal recessive gene, meaning that the animal has received one defective gene from each of its parents.

It is desirable to recognize congenital defects which are of significance to cattle owners and breeders. Not only is diagnosis important, but methods to control genetically induced defects should be available. The most frequently encountered defects seem to involve bone, brain, muscle and skin. In this chapter the more significant genetic diseases in beef and dairy cattle are reviewed.

Mulefoot. The single most common and economically important disease in Holstein, Angus, Chianina, Charolais and Simmental cattle is syndactyly (mulefoot). This is nondivision or fusion of functional toes. It affects most frequently the right front foot followed by the left, then right hind and all four feet. The cow is not adapted to the single hoof and walking is painful and difficult for mulefoot animals. Frequently they die due to stress.

Syndactyly is a simple autosomal recessive gene. It is common in various breeds in the United States and Europe. Other species affected are swine, sheep and dogs.

This ranks as the most important genetic disease in cattle in the United States.

Treatment is by control of carrier bulls in artificial insemination and natural breeding.

A method of early detection has been developed at Kansas State University. It combines superovulation, embryo transfer (two embryos for recipient), and early fetal cesarean section at 60 days of gestation at which time the mulefoot condition can be easily recognized.

Cows may also be tested in this way: The cows are superovulated and then inseminated with semen from an affected syndactylous bull. The embryos are transferred to recipient cows (two per recipient) and then the fetuses are removed by cesarean section at 60 days of gestation. It takes 7 normal fetuses per cow or bull to declare the suspect animal clean (a non-carrier). As outlined above, prevention can be accomplished only by preventing the use of carrier animals in breeding.

Too Many Toes. Polydactyly, more toes than normal, also is a genetic disease mostly in Simmental and Holstein cattle. It is transmitted as a polygenic (many genes with small effects). Usually one finds 3 toes on both front feet. The affected animals have difficulties in walking. Spread of this defect is by carrier bulls. There is no treatment. Prevention and control is only by carefully recording defective calves and removing carrier bulls from service.

"Snorter" dwarf with typical saddle nose, short legs and bloated belly. Dwarfs are rare today but once were a serious threat to livestock industry.