Comparison of efficiency of five heat synchronization protocols in Holstein cows during heat stress

The aim of this study was to compare the efficiency of five synchronization protocols, economically, in Holstein cows during heat stress. This experiment was conducted at a commercial dairy farm in summer 2015 (temperature humidity index 73–81). Five hundred Holstein dairy cows with ˃25 kg/d milk yield were randomly assigned to five experimental groups: 1) ovsynch; 2) presynch-ovsynch; 3) double ovsynch; 4) G7G-ovsynch and 5) PG7G-ovsynch. Results showed that synchronization rate was significantly lower in ovsynch compared to other protocols (P 0.05). Presynchronization of cows before initiation of ovsynch improved conception rates (CR) at 32 and 62 days (d) after AI compared to ovsynch protocol (P 0.05). According to the reproductive CR at 32 and 62 d after AI and pregnancy loss, it was found that G7G and PG7G were the best protocols compared to other protocols. The cost associated with the semen use per conception was highest at ovsynch and lowest at both G7G and PG7G protocols. Total costs per conception at 60 d after AI were lowest (1890000 rials) in G7G-ovsynch compared to other protocols. In conclusion, considering total costs associated with hormones and semen use per pregnancy, the G7G protocol is economically the most effective among the studied protocols.