Comparison of GnRH and hCG effects on oestradiol, progesterone and premature luteolysis in Ovsynch-synchronized ewes.

Abstract

The purpose of this study was to ascertain whether premature luteolysis can be alleviated by substituting the ovulation inducing agent hCG for GnRH. Seventy-two hours after the end of artificial insemination (AI), pluriparous Awassi ewes were randomly assigned to one of three treatment groups of 13 ewes each. First group received 37.5µg of the GnRH analog Lecirelin, the second 1000I.U hCG and the third group served as a control (received 1ml of physiological saline solution). Blood samples were collected at daily intervals after GnRH treatment and analysed for plasma oestradiol and progesterone concentrations. Ovarian follicles were monitored ultrasonically at the time of GnRH administration, 60hr and 84hr later. Pregnancy was diagnosed ultrasonically at Day 35 after AI. Number and size of ovarian follicles did not differ (p>.05) among treatment groups. Onset and duration of oestrus were not affected by treatment (p>.05). No significant differences (p>.05) were recorded in oestradiol and progesterone concentrations between the treatment groups during the inspection period. Premature luteolysis became evident in ewes with longer oestrous durations by Day 6.25 after AI and amounted to 7.69%, 18.18% and 23.07% in GnRH, hCG and Control groups respectively. Pregnancy rates increased to 92.31% and 81.82% in GnRH and hCG groups, compared to 76.92% in the Control group. The results indicate that GnRH was more effective in reducing premature luteolysis than hCG. Substituting hCG for GnRH as an ovulation inducing agent was of no avail.