A SECOND EXPERIMENT WITH HETEROSPERMIC INSEMINATION IN CATTLE

Abstract

Summary. Spermatozoa from four Friesian bulls were mixed in equal numbers. After insemination of the mixture, the paternity of calves was scored by blood-typing. Consistent results were obtained over replicate experiments conducted in each of 6 successive weeks. After insemination of `fresh' mixed semen, the number of calves sired per bull were in a ratio close to 1:1:1:1. Normal conception rate tests with fresh semen from one bull at a time (4- and 16-week non-return rates) also showed no significant differences in bull fertility. After inseminating mixtures subjected to deep-freezing at −196° C, the numbers of offspring were no longer nearly equal; one bull now sired ~50% of the progeny. It is concluded that bulls vary in the ability of their spermatozoa to withstand deep-freezing. No significant prediction of semen fertility based on staining affinity of spermatozoa could be realized, but the experiment was of limited size for this particular purpose. In two sets of twins, the co-twins were sired by different fathers. The sex ratio of progeny was unaffected. Experiments of this type offer no apparent risk to cooperating farmers, since overall conception rate was not diminished. Stocks of deep-frozen semen have been laid down for testing in subsequent years.