Treatment with bovine follicular fluid suppresses follicular development in gonadotrophin-releasing hormone-treated anoestrous ewes.

The role of FSH in gonadotrophin-releasing hormone (GnRH)-induced follicular development in anoestrous ewes was investigated using injections of bovine follicular fluid (bFF) to reduce plasma FSH levels. Groups of five animals were treated for 12 h with GnRH (250 ng at 2-h intervals) alone, GnRH plus bFF or saline alone, or for 36 h with GnRH alone, GnRH plus bFF or bFF alone. The administration of bFF (1.5 ml s.c. at 8-h intervals) significantly (P less than 0.05) reduced mean plasma FSH levels, but with the exception of animals treated with bFF alone, had no effect on LH levels. Treatment with bFF alone for 36 h resulted in a significant (P less than 0.05) increase in LH concentrations. There was considerable variation in the number of follicles greater than or equal to 2 mm in diameter in the treatment groups. The mean diameter, oestradiol secretion and number of 'oestrogenic' follicles were significantly (P less than 0.01) reduced in ewes treated with GnRH plus bFF or bFF alone for 36 h compared with those treated with GnRH alone. Testosterone secretion by the follicles was not affected by treatment. These results confirm previous findings that treatment with bFF decreases circulating FSH levels in anoestrous ewes and, moreover, that concurrent administration of bFF and GnRH inhibits the follicular maturation that is induced by treatment with GnRH alone, suggesting that FSH as well as LH is required for follicular maturation in the ewe.