Pregnancy rate of cows given synthetic gonadotrophin-releasing hormone at the time of service

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Abstract
A trial involving 25 herds was conducted in the Maffra area of Victoria [Australia] to study pregnancy rate after injection of synthetic Gn-RH at service. Of 3502 cows having a first service, 674 cows were injected by the farmer at first service with a single intramuscular injection of 250 .mu.g of synthetic Gn-RH, while the remaining 2828 cows acted as untreated controls. First service pregnancy rates were 58.8% in the group treated with Gn-RH and 54.1% in the untreated group, a 4.7% increase or an odds ratio of 1.21 (P < 0.05). However, adjustment for the potentially confounding variables calving to first service interval and herd reduced the odds ratio to 1.07 (P > 0.4). Treatment with Gn-RH at second or third service did not alter pregnancy rate to that service compared to untreated services. There was no interaction of treatment with Gn-RH at first service with calving to service interval. It is concluded that injection of 250 .mu.g of synthetic Gn-RH at the time of service does not increase pregnancy rate to that service.

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