Abstract

The aim of this study was to examine whether synchronization of ovulation using GnRH and PFG2a without estrus detection could be an effective method for improve reproductive performance in dairy cows. Healthy chilean black friesian cows (n=80) were divided into two groups (n=40): 1) control group (GC) cows inseminated 12 hours after oestrus detection, and 2) synchronized group (GS) received an initial injection of GnRH (0.02mg buserelina) at a random stage of the oestrus cycle. Seven days later they received PFG2? (25 mg dinoprost), and forty-eight hours later cows were treated again by GnRH. IA was performed 18 hrs after the second injection of GnRH. The reproductive activity was controlled trough progesterone concentration in milk and rectal palpation. First service conception rate in both groups were similar (50% and 47.5%), however first service was realized 31 days before in GS groups (P>0.05). The interval between partum to conception was greater (P>0.05) in the GC group (145.5 ± 65 days) than in GS cows (100.5 ± 45). Services per conception were similar in both groups (GC=1.87 and GS =1.75). In conclusion the synchronization of ovulation without estrus detection is an effective method for decreasing open days in dairy herds.