Induced termination of the calving season in a large dairy herd

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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.