Use of Gonadotrophins to Synchronize Estrous Cycles in Swine

A total of 105 gilts and sows were used in a study designed to develop a method for synchronizing estrous cycles of swine. Experimental estrous cycles were established by inducing ovulation with an intramuscular injection of 1200 I.U. of PMS, followed in 3 days by intravenous injection of 500 I.U. of HCG or intramuscular injection of 1000 I.U. of HCG. Mode of injection of HCG was without a detectable influence on response. The average interval from the injection of HCG to the first post-treatment estrus was 21.9 days. Ninety-six percent of the injected gilts and sows exhibited estrus 18 to 28 days following the injection of HCG. Animals exhibiting estrus during an interval of 5 days varied from 64 to 100% for eight experimental groups of animals. The fertility level of the first post-treatment estrus was at least equal to that of comparable groups of nontreated animals as measured by conception rate, fertilization rate, average number of embryos on the 25th day of pregnancy and litter size at farrowing. This procedure of using gonadotrophin injections to synchronize estrous cycles in swine provides an effective and dependable means of reducing variability in breeding dates without decreasing subsequent reproductive performance.