INFLUENCE OF SEXUAL ACTIVITY ON SERUM LEVELS OF LH AND TESTOSTERONE IN THE RAM

Abstract

Two experiments were conducted in January to study the influence of various types of sexual activity on serum levels of LH and testosterone (T) in the ram. Serum LH and T were determined by radioimmunoassay, LH values being expressed in terms of ng NIH-LH-S14/ml. In the first experiment, seven Finnish Landrace rams, 11 mo to 3 yr of age, were allowed individually to mate once (day 1) and continuously mount without intromission for 2 min (day 2) an estrual ewe. Jugular blood (6 ml) was collected by venipuncture at 20-min intervals for at least 2 h prior to and following each type of sexual activity. Two hours following mounting activity on day 2, estrual ewes were walked in front of the rams for 5 min. Blood was collected from each ram at 10 and 30 min following this observation period. Several serum peaks (4–8) of LH occurred in all rams over the two sampling periods (9 h). Although a rise in LH followed one or more of the types of sexual stimulation in four of the seven rams, no consistent relationship was noted between sexual stimulation and LH peaks. In a second experiment, serum samples were obtained every 20 min for two separate 24-h periods, 1 wk apart, from two 3-yr-old Finnish Landrace rams. During the first 24-h period, the rams were penned individually; during the second period each was penned with an estrual ewe. Numerous matings (44 and 24) were recorded for the rams during the latter period, 74% of which took place during the first 12 h. The serum profiles of LH and T during the first 24-h period were characterized by periodic peaks of LH associated with similar changes in T. These profiles appeared to be influenced markedly by sexual activity during the second 24-h period. Higher baseline and mean serum levels of both hormones and a greater number of serum peaks of LH and T were observed during the first 12 h. The serum levels of both hormones then decreased sharply at 13–14 h and remained low for 8–10 h, even though mating occurred periodically during this time. Subsequently, a further serum peak of LH and T was observed before the end of the sampling period.