EFFECT OF TREATMENT WITH GnRH OR HCG ON DAY 5 AFTER ARTIFICIAL INSEMINATION ON LUTEAL ACTIVITY OF DAIRY COWS
The objective of this study was to compare the effect of human chorionic gonadotrophin (hCG) and gonadotropin releasing hormone (GnRH) administration on day 5 after artificial insemination (AI) on luteal function. Thirty-three dairy cows were synchronized by the Ovsynch protocol and assigned randomly into 3 equal groups to receive on day 5 after AI 1500UI hCG, 100µg GnRH, and 2mL saline solution (Control), respectively. progesterone concentration (P4) in blood was measured every 3 days from day 5 to 23 after timed AI. Ultrasound examination of ovaries was performed on days -10, 0 (day of AI), 2, 5, 8, 11 and 14. The results revealed a development of an accessory corpus luteum(CL), 100% in the group received GnRH and 90.9% in that received hCG. No accessory corpus luteum in control group was observed. Total luteal tissue area on the ovaries was increased in hCG and GnRH group compared to control. Plasma P4 concentration was significantly (P < 0.05) higher in hCG and GnRH groups than control after day 11 AI. The comparison treatments showed that total luteum tissue aerea and P4 concentration were lower in GnRH group than in hCG one.