THE EFFECT OF GNRH ANALOG (BUSERELIN) TREATMENT ON DAY-12 POST MATINGON OVARIAN STRUCTURE AND PLASMA PROGESTERONE AND ESTRADIOL CONCENTRATION IN EWES

An investigation was conducted into the effect of buserelin treatment on day 12 post mating on ovarian function and plasma progesterone and oestradiol-17 beta concentration in ewes. Changes in ovarian structure s were determined, at laparoscopy or after slaughter, 48 h after treat ment in 38 control and 41 ewes given an injection of 4 mu g buserelin on day 12 post mating (day 0=day of oestrus). Ovulation rate was highe r in buserelin treated (2.76) than in control (1.87) ewes (P <0.05). M oreover, 41 of the 113 corpora lutea observed in the buserelin group w ere the result of ovulations that had occurred within 48 h post treatm ent, compared with two of 71 in the controls (P <0.05). Blood samples were collected from 10 ewes in each treatment group for hormone analys is. Mean progesterone concentrations tended to be higher, in samples c ollected from 2 to 6 h post treatment, in the buserelin group (4.31 (s .e. 1.32) mu g/l) compared with the control group (3.71 (s.e. 1.44) mu g/l. Furthermore, overall mean oestradiol concentrations were lower, during days 13, 14 and 15 post mating, in buserelin treated (0.72 (s.e . 0.26) ng/l) than in control (0.94 (s.e. 0.50) ng/l) ewes (P <0.05). The results of this study indicate that buserelin treatment on day 22 post mating changes ovarian function.