Further Studies Concerning Sex-Limited Genetic Infertility in Cattle

presented evidence indicating that a recessive autosomal gone conditioned infertility in certain Jersey and Holstein heifers of the California Agricultural Expriment Station herd. In an effort to exclude cases of sterility of environmental origin, the sterility considered was limited to heifers unable to produce calves when mated to known fertile bulls. Thus, any cow that had produced one calf was considered fertile even though she might be unable to reproduce thereafter. The same definition for fertility and Sterility used for females in the earlier report (3) is used in this paper. The objectives contrast sharply with that of Tanabe and Casida (8), whose experiment was designed to study the nature of sterility of environmental or developmental origin. They purposely excluded from consideration all heifers that had never produced a calf, using only cows that had given birth to one or more calves prior to becoming infertile. In the 104 cows observed, they found that 10.6 per cent had abnormalities of the genital tract. This included 8.7 per cent in which the anomaly constituted a barrier to fertilization. Of the cows possessing normal genitals, 66.1 per cent had normal fertilized ova 3 days after mating, while the percentage of normal embryos had dropped to 23.1 per cent 34 days after mating. Reproductive performance at 34 days after mating was as follows: (a) failure of fertilization, 39.7 per cent; (b) embryonic abnormalities before 34 days post coitus, 39.2 per cent; and (c) normal embryos, 21.1 per cent.