An experimental study of heredity in bovine tuberculosis

Abstract

This study was conducted on what is probably the most valuable herd of Holstein Fresian cattle in the world. It has now extended over about ten years, hence several successive generations of stock have been studied under precisely similar conditions. The experiments have been supervised and verified by officers from the U. S. Department of Agriculture and the data are matters of official record in the register published by the Holstein Fresian Association. I am permitted to summarize and publish the results of the experiments by Mr. J. W. Dimick, the proprietor of Woodcrest Farm, where the problem is under study.

The number of animals comprised in the study is 425. The animals were originally selected because of their desirability from the standpoint of breeders and milkers or because of their “type” and entirely independent of their being or not being tuberculous.

The tuberculous animals greatly outnumbered the non-tuberculous and in most instances several generations of tuberculosis on both sides is known to have existed. 300 tuberculous animals were studied. The existence of tuberculosis was determined by the administration of treble the official dose of tuberculin, repeated in non-reacting animals three times at intervals of six months. All animals reacting to either test were removed at once to the tuberculous farm, the administration of which is entirely separate from that of the non-reacting herd. Little or no possibility of the transmission of infection from the tuberculous group to the healthy one exists.

With few exceptions tuberculous cows are bred to tuberculous bulls, the selection in any case is made for purposes of “type” and no account of the infection is taken in so far as breeding is concerned.

At birth the calves are immediately taken from the mother and no possible communication thenceforth exists between them except that the calf is given by bottle one feeding of the first milk secretion of the mother, removed by stripping and fed unsterilized.