The Effect of GnRH Injection on Plasma Progesterone Concentrations, Conception Rate and Ovulation Rate in Iranian Holstein Cows

Ovarian functional disorders are reported as an important cause of infertility in dairy cattle. This experiment was carried out to determine the effects of GnRH injection at the time of insemination on ovulation rate, Conception rate and plasma progesterone concentrations on day 5 post AI. Egithy cows were randomly assigned into 2 experimental groups: Treatment group (n = 40) which received 15 ug of GnRH and control group (n = 40) without any hormonal treatment. Cows were palpated per rectum to ascertain the occurrence of ovulation 24 h post AI. Blood samples were drawn on the day of insemination and on the day 5 post AI. Plasma concentrations of P-4 were measured by RIA and analyzed by means of the GLM procedure of the SAS. Differences between the two experimental groups were analyzed by one way ANOVA. Ovulation rate and conception rate were analyzed by means of Binary Models of the SPSS. Results of this study indicated that the injection of GnRH increased the ovulation rate insignificantly (65% vs 47.5%, p>0.05) and increased conception rate significantly (55% vs 25%, p<0.03). GnRH administration caused an insignificant increase in the concentration of plasma progesterone on day 5 post AI (6.03 vs. 5.27 ng mL(-1), p<0.02). In general results of this study indicate that GnRH injection at the time of artificial insemination improves ovulation and pregnancy rates.