Induced termination of the calving season in a large dairy herd

Abstract

The calving season of a 550-cow dairy herd was shortened by the induction of premature parturition in 231 cows and heifers, using the synthetic or natural prostaglandins cloprostenol or PGF₂ alpha as the sole treatment, or these agents 8 and 12 days after dexamethasone trimethyl acetate (DTMA), depending on estimated prematurity at the time of first injection. A series of synchronised batch-calvings was produced in the cows, with 85% of the PG group calving within 96 hours of treatment, 97% of the DTMA — 8 days — PG group calving within 48 hours, and 100% of the DTMA — 12 days — PG group calving within 72 hours. PGF₂ alpha was associated with very rapid deliveries and dystocia due to incomplete cervical dilation. Cow and calf survival was high. Eighty-three percent of those mated conceived, 78% of them in the first 8 weeks of mating, despite an incidence of incomplete membrane-expulsion that exceeded 40%. Some conceptions to first service did not progress beyond 6–7 weeks of gestation. In nearly all these cases, the animals conceived at a later service, usually at the first oestrus after expulsion.

The results indicate that acceptable results can be obtained in cows within 2 weeks of term using cloprostenol alone. Treatment regimes that allow a priming dose of depot corticosteroid to precede cloprostenol should be used for terminating less advanced pregnancies.