Secretory Patterns and Circadian and Seasonal Changes in Luteinizing Hormone, Follicle Stimulating Hormone, Prolactin and Testosterone in the Male Pygmy Goat1

Abstract

Four male pygmy goats were 9 months of age when assigned to this experiment. They were maintained for 1 year beginning in June 1975 under natural photoperiod changes characteristic of southern Canada and ambient barn temperatures ranging from 5 to 25 C. During the third week of each month, bucks were bled from a jugular vein by venipuncture at 30-min intervals for either 12 or 24 hr (August, November, February and May). Sera were assayed for luteinizing hormone (LH), follicle stimulating hormone (FSH), prolactin (PRL) and testosterone (T) by radioimmunoassay. Both LH and T were secreted episodically, and increases in serum LH were generally followed by increased serum T concentrations which peaked within 60 minutes. Mean serum LH, T and PRL concentrations fluctuated considerably over the 24-hr periods with peak PRL concentrations generally occurring during the dark period. However, serum FSH concentrations did not show a pulsatile profile and variations over the 24-hr were minimal. Serum LH and T increased with decreasing daylength and attained maximum mean values (± SE) in October of 1.9 ± .5 ng NIH-LH-S14/ml and 15.4 ± .9 ng/ml, respectively. These increases were a result of higher baseline levels and peak frequencies. Lowest mean serum concentrations of LH (.4 ± ,1 ng/ml) and T (2.3 ± .5 ng/ml) occurred in November and June, respectively. Serum FSH increased slightly in September, but the highest concentration occurred in April (67.8 ± 4.4 ng NIH-FSH-S6/ml). Changes in serum PRL concentration paralleled changes in daylength (r = .58, P<.05). Seasonal changes in serum concentrations of LH, PRL, and T in the male pygmy goat follow closely the changes that have been reported for rams, which are also a seasonal breeder under temperate climatic conditions.