Fertility of heifers and suckled cows inseminated at predetermined intervals after treatment with prostaglandin F2α

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Abstract
SUMMARY: Heifers and suckled cows in 34 herds were included in a field trial using prostaglandin F2α (PGF2α) to control ovulation. Oestrus was induced by two intramuscular injections of PGF2α 10–12 days apart in 592 animals. Of these, 264 were inseminated once at 80 h and 328 were inseminated twice, at 70 and 88 h, after the second injection of PGF2α. Pregnanoy was confirmed by palpation or by calving without further insemination. After adjustment for independent sources of variation in fertility, estimated true pregnancy rates were 59·6 ± 3·0% for cattle inseminated once, and 61·3 ± 2·7% for those inseminated twice at one oestrus, compared with 66·4 ± 3·2% for 220 animals allowed to cycle normally in the same herds (controls).In a sub-sample of 538 animals, semen usage was 15% higher for the treated group inseminated once and 107% higher for the group inseminated twice, than for the controls. The breeding season extended over about 80 days for the control groups, and about 30 days for the treated groups.No side effects attributable to prostaglandin were observed among the treated cattle.