Clinical effect of buserelin on pregnancy rates in cattle

Abstract

The trial used 2530 recorded services of 1619 animals on 19 dairy farms. Alternate cows were injected intramuscular with 10μg buserelin, a GnRH analogue (Receptal, Hoechst UK), 11 days after insemination. The pregnancy rate was calculated for control and treated cows, paired for calving to first service interval, parity and week of service. For 520 paired control and treated cows the pregnancy rate to first service was 50.6% and 60%, respectively (p <0.01). For second and subsequent services each cow was grouped according to treatment or control status in the preceding dioestrus period, in addition to day 11 after service. This gave three treated groups: treated, treated (TT); treated, control (TC); and control, treated (CT) which could then be compared to the control, control (CC) group. For 136 paired CC and CT cows the pregnancy rate to second service was 41.2% and 54.4% respectively (p <0.05). For 67 paired CC and CT cows the pregnancy rate to third service or more was 23.9% and 52.2% respectively (p <0.001). For 40 paired CC and TT cows the pregnancy rate to third service or more was 15.0% and 45.0% respectively (p <0.01). The increased pregnancy rate after treatment was associated with a reduction in the number of cows with interoestrus intervals of 11-17 days compared with control cows (2% vs. 7%, p <0.01).