Ovarian inhibin content and sensitivity to inhibin in Booroola and control strain Merino ewes

Abstract

The inhibin content of ovaries collected from highly fecund Booroola Merino ewes was only one third that of control Merino ewes. Ovariectomized ewes of both strains were treated with charcoal-treated ovine follicular fluid for 2 days. A dose-dependent effect on plasma FSH was observed: maximum FSH suppression was observed on the day after the last injection of follicular fluid. Ewes receiving the highest dose of follicular fluid (total dose 72000 units of inhibin) had FSH levels depressed to only 8% of pre-treatment levels. Booroola ewes showed FSH suppression 1 day earlier than control ewes but otherwise the responses of the two strains to follicular fluid were similar. Plasma LH levels were only slightly depressed with the highest dose of follicular fluid. These results suggest that the feedback relationship of inhibin and FSH in Booroola ewes may be set differently from that in control ewes and this may contribute to the difference in ovulation rate between ewes of the two genotypes.

Use of bovine follicular fluid to increase ovulation rate or prevent ovulation in sheep

“…Follicular diameter (mm) Fig. 3 (Miller et al, 1979;Miller, Crit¬ ser & Ginther, 1982;Cummins et al, 1983;McNeilly, 1984) the dose-dependency of observed effects or the consequence at the ovarian level of follicular fluid treatment have not been reported hitherto. The dose-related increase in time to oestrus after bFF administration was probably a consequence of the suppression of plasma FSH concentrations; the lower FSH concentrations were the longer oestrus was delayed.…”

Variations in patterns of follicle development in prolific breeds of sheep

“…Follicular response to LH is also acquired in smaller follicles in Booroola ewes compared to Merino ewes (Scaramuzzi, Turnbull, Downing & Bindon, 1981). Furthermore, decreased ovarian inhibin content has been found in Booroola Merino ewes compared to the prolific Merino and control Merino ewes (Cummins, O'Shea, Bindon, Lee & Findlay, 1983;Bindon, 1984). These between-breed and strain differences suggest that each breed might have a different mechanism by which ovulation rate is controlled.…”

Pituitary gonadotrophins in Booroola and control Merino sheep

“…Also, compensatory ovulation after unilateral ovariectomy is associated with a transient increase in FSH secretion (Findlay & Cumming, 1977). The inhibin content of the ovaries of Booroola ewes is only one third that of control Merinos (Cummins, O'Shea, Bindon, Lee & Findlay, 1983), suggesting that peripheral FSH concentrations in Booroola ewes are likely to be higher than in control ewes. However, attempts to establish a relationship between peripheral FSH concentrations and ovulation rate in the adult Booroola Merino during the oestrous cycle have been unsuccessful (Bindon, Findlay & Piper, 1982), despite earlier observations that prepubertal Booroola ewe lambs have higher peripheral FSH concentrations than do control Merinos (Findlay & Bindon, 1976).…”