PATTERNS OF GONADOTROPIN-SECRETION IN CYCLIC FINN EWES SELECTED FOR AND AGAINST HIGH OVULATION RATE

A comparison of the patterns of LH and FSH secretion was undertaken in lines of Finn sheep selected for and against high ovulation rate, Mea n ovulation rate was significantly higher in the high line ewes (mean 4.1) compared with both the control (mean 2.5) and low line (mean 2.7) ewes (P < 0.01). The pre-ovulatory LH peak occurred significantly ear lier in the high line ewes (mean 52.1 h) compared with both the contro l (mean 65.0 h) and low line (mean 59.0 h) ewes (P < 0.05). While mean LH pulse frequency and overall mean LH concentrations were both signi ficantly higher during the follicular compared with the luteal phase o f the cycle (P < 0.05), there were no consistent relationships between patterns of pulsatile LH secretion and ovulation rate among the three selection lines. Plasma FSH concentrations remained significantly hig her over the entire follicular phase of the oestrous cycle in the high line ewes compared with both the control and low line ewes (P < 0.05) . It is suggested that the ovulation rate achieved by high line ewes m ay be causally related to their higher follicular phase FSH concentrat ions.