The effect of pre-mating injection of an analogue of gonadotrophin-releasing hormone (GnRH) on pregnancy rates to first insemination in dairy cattle

E.D. Fielden, K. Moller

Department of Veterinary Clinical Sciences, Massey University

Proceedings of the New Zealand Society of Animal Production. 1983, 43: 59-62

Seven trials were conducted during 3 breeding seasons where half the animals in each trial herd received a subcutaneous injection of 10µg GnRH analogue (Receptal, Hoechst A.G.) 0 to 6 hours before insemination while the other half were injected with a placebo. In 4 of the trial herds animals were divided into 2 further sub-groups depending on the time they were observed in oestrus relative to the time of insemination.

Cows to be mated each day were paired within sub-groups within trial for age and condition score; 1 of each pair was treated with the drug the other with the placebo. The same batch of semen and the same technician were used within each trial herd on any particular day.

Pregnancy rates to first insemination for 655 Receptal treated cows were 5.9% higher than for 647 placebo treated cows (P<0.05). Herd differences in pregnancy rates were observed (P<0.001) but no significant interactions between either herd and treatment or between time when the cows were seen in oestrus and treatment were noted. Present results suggest that should this regime be used to enhance pregnancy rates to first matings all cows should be treated.

Keywords: NZSAPAB; First service; pregnancy rates; dairy cattle injected GnRH analogue

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Last Updated 03-05-1997