Effect of GnRH-treatment on, the pregnancy of dairy cows

The authors treated, in two series of experiments, dairy cows with 50 mu g of GnRH-analogue preparation (1.0 ml Gonavet Veyx) for the purpose of increasing progesterone production of corpus luteum (CL) and thus, increasing the chance of pregnancy. In the first experiment GnRH was given im. on 12(th) day after insemination following induced oestrus to cows with functioning CL (n=154). Compared to control cows (n=168), pregnancy rate was higher with 9.4% (p < 0.01) in treated cows. Increase in pregnancy rate was significant in first calving cows (17.5%, p < 0.01) and in case of first insemination after calving (14.4%, p < 0.01). The difference was significant between second inseminations and inseminations within 200 days following calving. In the second series of experiments 490 dairy cows of four dairies were treated im. with GnRH-analogue preparation on the 4(th) (5(th)) day following insemination for helping marked progesterone increase and faster embryo development. Compared to 492 control cows, in three dairies minimal difference was found in favour of treated animals. The authors recommend in long-term the treatment around 12(th) day, easily built in reproductive technology, in dairies where oestrus and/or ovulation synchronisation is made regularly (by prosynch, ovsynch, etc. methods).