Effects of two different protocols: injection of progesterone vs. injection of GnRH+PGF2a on the onset of estrus in dairy cows with postpartum anestrous

Postpartum anestrous is one of the most important problems in the dairy industry in the world and especially in Iran. The objective of present study was to compare the efficacy of two hormonal programs for recycling of postpartum anestrous cows. For this reason, 230 Holstein cows from 4 similar dairy herds (with totally 2560 cow and unique management and feeding system) located on the suburb of Tabriz (North-west of Iran) were examined during April 2012 to August2013. These cows showed no visible oestrus signs until the minimum 60 days postpartum. Clinical examinations were performed twice, with a 10 days interval, and blood samples for progesterone analysis were collected simultaneously with every rectal palpation. Based on progesterone values and clinical examinations only cows with lower progesterone levels (P4<2ngr/ml) at both sampling and nonfunctional ovaries (at two consecutive examinations) were randomly allocated into three groups: A, B (n=100) and C (n=30). Cows in group A were administered a combination of Gonadotropin releasing hormone (GnRH) on day 1 and prostaglandin F2alpha on day 8; cows in group B were administered 125 mg of progesterone for 8 days, whereas cows in the control group C were given placebo. Subsequently all cows were examined for signs of estrus and performed artificial insemination on two consecutive estrus following treatment. In groups A & B  the rates of observed oestrus, first service conception rates and second service conception rates were 5%  vs. 68%, 60%  vs. 25% and100% vs. 64.7% respectively. In the group of C, cows were not observed in estrous.  Significant differences were observed between groups in all fields (p≤0.01). Thus based on the current study it can be concluded that for recycling postpartum anoestrus cows, progesterone therapy is the treatment of choice.