FSH in the ewe: effects of season, live weight and plane of nutrition on plasma FSH and ovulation rate

The concentrations of FSH (ng NIH-FSH-S6/ml) were measured by specific radioimmunoassay in jugular vein plasmas of 3 groups of ewes fed complete rations of alfalfa hay providing either 1/3 of a maintenance (M) requirement (1/3M, n=16), M (n=12) or 2M (n=9). The ewes were bled on different, known days of their estrous cycle and records of live weight (LW) and ovulation rate (OR) at the time of blood sampling were recorded. After 7 weeks the mean LW of the 3 groups (1/3M, 35 kg; M, 42 kg; 2M, 49 kg) reflected the differential nutrition. The OR (1/3M, 0.94; M, 1.17; 2M, 1.89) was highest (P0.05) than the MCR of FSH (0.621 ml/min/kg) in 8 ewes with 2 ovulations. The FSH response to GnRH (2.5 µg/h for 4.5 h), measured 2 days after the MCR studies, appeared to be inversely related to number of corpora lutea (0.05