The fertility of heifers inseminated at predetermined intervals following treatment with MGA and HCG to control ovulation

Abstract

Oestrus and the time of ovulation were controlled in 87 mature nonpregnant heifers by using silastic implants of melengestrol acetate (MGA) followed by an injection of HCG 48 hr after removal of the implants. The heifers were allocated at random to three groups and inseminated with frozen semen before the estimated time of ovulation. Animals in Groups 1 and 2 were inseminated once at 14 and 24 hr, respectively, after HCG, while animals in Group 3 were inseminated twice 14 and 24 hr after HCG. All heats observed after insemination were recorded until the animals were killed 55 days later, when 23% of them were found to be pregnant. The conception rate was not affected by changing the time or the frequency of insemination. Possible reasons for the low fertility are discussed.