Changes in FSH and the pulsatile secretion of LH during the delay in oestrus induced by treatment of ewes with bovine follicular fluid.

Treatment of Welsh Mountain ewes with i.v. injections of untreated or charcoal-treated bovine follicular fluid (BFF) after prostaglandin-induced luteal regression resulted in a significant delay in the onset of oestrous behaviour. Injections of BFF caused a significant decrease in plasma concentrations of FSH but levels were only suppressed below those in control ewes during the first 24 h of the 48-h period of treatment. At the end of BFF treatment there was a substantial increase in plasma FSH levels. In contrast, there were no significant effects of BFF treatment on basal plasma concentrations of LH or pulse frequency or amplitude of LH secretion. Corpus luteum function, as measured by plasma concentrations of progesterone, in BFF-treated ewes was normal. These results suggest that the delay in oestrus caused by treatment of ewes with BFF is due to a specific suppression of plasma levels of FSH while LH secretion remains unaffected.