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