EFFECT OF BOVINE FOLLICULAR-FLUID TREATMENT AND PROGESTERONE PRIMING ON LUTEAL FUNCTION IN GNRH-TREATED SEASONALLY ANESTROUS EWES

The main objective of the present experiment was to investigate whethe r progesterone priming eliminates defective luteal function in seasona lly anoestrous ewes induced to ovulate with pulsatile GnRH treatment b y synchronizing the early stages of follicle development. This was ach ieved by suppressing and synchronizing the early stages of follicle de velopment with bovine follicular fluid (bFF) and then investigating wh ether this was sufficient to eliminate defective luteal function follo wing the induction of ovulation with GnRH. Ewes in group 1 (no. = 10) were injected s.c. with 2 ml bFF at 8-h intervals for a period of 3 da ys before the start of GnRH treatment. Animals in group 2 (no. = 10), which served as positive controls, were given a single i.m. injection of 20 mg progesterone 3 days before the start of GnRH treatment, while those in group 3 (no. = 10), which served as negative controls, were injected with corn oil alone at this time. Ewes in all the three group s were induced to ovulate by administration of 2-hourly injections of GnRH (250 ng per injection) for 54 h. Frequent blood samples for LH, F SH, and oestradiol were collected around the time of both progesterone /bFF injections and GnRH treatment, as well as daily thereafter to mon itor luteal function. The bFF injections given to animals in group 1 r esulted in a significant (P < 0.001) suppression of FSH concentrations , followed by a rebound vise in concentrations after thee cessation of treatment. GnRH treatment significantly (P < 0.05) increased both mea n LH pulse amplitude and overall mean LH concentrations in all the thr ee groups, while LH pulse frequency was increased only in non-bFF-trea ted ewes. Plasma oestradiol concentrations 24 h after the start of GnR H treatment were significantly (P < 0.05) higher in groups 2 and 3 com pared with group 1. These differences in the patterns of oestradiol co ncentrations over time were associated with a significant (P < 0.05) d elay in the onset of the pre-ovulatory LH surge in ewes treated with b FF (group 1). However, there was no difference in either the duration or the height of pre-ovulatory LH surge between the LH ee treatment gr oups. Ewes in all three treatment groups ovulated in response to GnRH treatment. However, both laparoscopic examination and plasma progester one concentrations revealed that the incidence of normal luteal Juncti on was significantly (P < 0.05) higher in group 2 (10/10) compared wit h groups 1 (2/10) and 3 (4/10), with no difference between groups 1 an d 3. Overall, these results suggest that progesterone priming does not eliminate defective luteal function through synchronizing early stage s of follicle development.