Comparsion the effect of HCG and GnRH administration on Day 5 after AI on conception rate of Dairy cattle under heat stress conditions

When dairy cattle are subjected to heat stress, reproductive efficiency declines.To override the suppressive effects of heat stress various environmental and hormonal manipulations have been utilized. The aim of the present study was to evaluate whether the administration of GnRH and hCG on day 5 post-insemination would improve pregnancy rate in mild heat stressed dairy cattle (summer months). All cows were inseminated at estrus and then on days 5 after AI, they were alternately assigned into three groups: GnRH group(n=44)received an IM injection (5ml) of GnRH (GONAbreed®,PARNEL, Australia,) hCG group (n=44) received an IM injection (1ml) of hCG (Pregnyl®, Daru Pakhsh, Iran) and control group (n=36) which did not received any treatment.Pregnancy was diagnosed on day 32-39 after AI by ultrasonography.. The difference in CR among three groups were analyzed by using chi-square and fisher test. CR in GnRH, hCG and control groups were 54/5%, 61% and 58/3% respectively, that weren’t significant difference among three groups (P>0.05). CR within GnRH groups in ≤150 and>150 days open subgroups were 72%, 40% that is statistically significant (P<0.05) and also CR between GnRH and hCG groups based on Open days>15o was 40%, 76% that is statistically significant (P<0.05). CR within control and hCG groups among <3 and≥3number of AI were 80%, 31%, 77% and 39%respectively, that is statistically different(P<0.05). According to the results of this study, the use of hCG after AI in repeat breeder dairy cows in summer months is recommended.