Changes in the Profiles of Serum LH, FSH and Testosterone, and in Mating Performance and Ejaculate Volume in the Ram during the Ovine Breeding Season3

Abstract

Changes in profiles of serum luteinizing hormone (LH), follicle stimulating hormone (FSH) and testosterone and in mating performance and ejaculate volume have been determined in Finnish Landrace (Finn) and Managra Synthetic (Line-M) rams during the ovine breeding season. In early August, mid-September, early November and mid-December four rams of each breed were bled by venipuncture from the jugular vein at 20-min intervals for two 8-hr periods. Rams were bled while in the absence (control period) and presence (mating period) of ewes in estradiol-induced estrus. An ejaculate was also collected from either five or six of the rams during these months. Aliquots of serum were assayed for LH, FSH and testosterone by radioimmunoassay. Testosterone concentrations in seminal plasma were also determined. Episodic increases in serum levels of LH and testosterone were evident in all rams during each 8-hr period, while FSH fluctuated very little from baseline concentrations (usually <50%). Pulses of LH were consistently followed by elevations in testosterone which peaked within 60 minutes. Progressive changes in the profiles of serum LH and testosterone occurred in rams of both breeds as the breeding season advanced. Peaks in LH became more frequent and decreased in height, and the number and height of the testosterone peaks increased. Serum FSH concentrations were highest in September. Mating activity was associated with increases in the frequency of LH and testosterone peaks in August and September. The number of matings per 8 hr and ejaculate volume increased between early August and early November; both were highest in November when the level of serum testosterone was maximal. Mating performance and mean testosterone concentration (control period) were positively correlated within rams across months (r = .90, P<.01) and between rams only in August (r = .76, P<.05). Monthly changes in testosterone concentration in seminal plasma were moderate compared with those in serum. Direction changes in seminal plasma testosterone were similar to those in serum FSH. Copyright © 1977. American Society of Animal Science . Copyright 1977 by American Society of Animal Science.