Sinister Gene

Cattle breeders are in a fluster about dwarf calves, which are being born in ever-increasing numbers in the U.S. and Canada, and cattle experts are building up herds of dwarfs for study. Last week Professor E. W. Stringam of the University, of Manitoba was tenderly nursing a bull calf which he and assistants had delivered by Caesarean section from a dwarf cow. The calf, sired by a normal young bull, is normal in proportions. It will outweigh its mother in three months, but it probably carries the taint of hereditary dwarfism.

Geneticists believe that dwarfism is a classic example of Mendelian inheritance, and that it is caused by a single recessive gene. A bull may appear normal, but if it carries the gene of dwarfism and is mated to a carrier cow, one-quarter of their progeny will on the average be dwarfs, one-half will be carriers, and one-quarter will be dwarf-free. If the carrier bull is mated to a dwarf-free cow, no dwarfs will appear in the first generation, but half of the calves will be carriers.

Dwarfs into Sausage. Dwarfs mated to dwarfs produce all dwarfs, but although dwarfs are potentially fertile, they rarely reach breeding age. Many are born dead or die soon after birth. Those that live to maturity grow about half the size of normal beef cattle. They wheeze and stagger; their bellies swell, and they often die of bloat. Dwarf beef is of poor quality. Most dwarfs that go to market are ground into sausage.

Cattle have always produced a few dwarfs, just as humans do. But stunted cattle were never common until about seven years ago, when they began to increase alarmingly in all three leading beef breeds--Shorthorn, Hereford and Aberdeen Angus. The increase has continued ever since.

Cattlemen prefer to say nothing about their dwarfs and get rid of them quietly. It hurts the value of a herd if too many little monsters are staggering around the range. So no one knows how many there are. Estimates of the proportion of dwarfs in beef breeds have gone as high as 7%. Some unfortunate herds have produced 12%, and the figures might be higher if cattlemen did not conceal their monsters. Considerably less than 12% of dwarfs can bankrupt a cattleman.

Bump on the Forehead. Cattle experts believe that the epidemic of dwarfism may be a result of breeding beef cattle for squat, spraddle-legged, "blocky" figures. This type wins prizes in shows and brings high prices at the stockyards, but animals selected for their blocky shape may be precisely the ones most likely to be carriers of dwarfism. The dwarfs are blocky too, and in other ways are caricatures of the beef-cattle ideal. An expensive, aristocratic bull may be the cause of a bad outbreak of dwarfism.

The only way to be sure that a bull is clean is to mate him to at least 15 carrier cows and see if his calves are ever dwarfs. This takes a long time, so the cattle experts are trying hard to find some other system. Dr. Paul Wallace Gregory of the University of California at Davis has invented a "profilometer," an instrument to detect the slight bump on a bull's forehead which shows that he may be a carrier. Sometimes X rays are used to look for the "crumpled" vertebrae that carriers sometimes have. Chief obstacle to cleaning the herds of carriers is the cattle fanciers' love of low-slung critters likely to carry the sinister gene.

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