Document Type : Research Paper
Assistant Professor, Department of Animal Science, Sari Agricultural Science and Natural Resources University, Sari, Iran, P. O. Box 578
The objective of this study was to compare the effect of five estrous synchronization protocols on ovulatory follicle diameter, progesterone concentration at AI and days 5 and 12 after AI and conception rate in Holstein cows during heat stress. Holstein cows (n=250) with more than 30 kg/d milk yield were randomly assigned to one of 5 experimental groups, 1) ovsynch (OV); 2) presynch-ovsynch (PO); 3) double ovsynch (DO); 4) G7G-ovsynch (G7G) and 5) PG7G-ovsynch (PG7G).Results showed that ovulatory follicle diameter was smaller in cows synchronized with OV protocol compared to other protocols (P˂0.05). Progesterone concentration at days 5 and 12 post AI was lower in OV protocol compared to other protocols (P˂0.05). Conception rates at days 32 and 62 post AI were lower in OV protocol compared to other protocols (P˂0.05).There was no difference among other synchronization protocols (P <0.05).In conclusion, results of present study showed that using presyhcnronization before initiation of Ovsynch can increase PR/AI of Holstein cows during heat stress.