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Lack of a nocturnal rise in serum concentrations of melatonin preceding the onset of puberty in gilts.
A. L. Bollinger*, M. E. Wilson, A. E. Pusateri, and M. A. Diekman
Purdue University, West Lafayette, IN.
Twenty prepubertal crossbred gilts (Yorkshire x Hampshire x Duroc) weighing 91.8 ± 4.2 kg at 5 mo of age were placed in an environmentally controlled room with a temperature of 18°C and light-dark cycle of 12:12. Light intensity at eye level of the gilts measured 700 lux. Three mature ewes were penned adjacent to the gilts to serve as positive controls. After a 30-day acclimation period, 10 gilts from the pool shown to be prepubertal (serum progesterone <500 pg/ml) received surgically implanted jugular catheters. Blood samples were drawn at 1100, 1130 and 1200 hours (4 hours after light) and 2300, 2330 and 2400 hours (4 hours after darkness) for 4 days. Red-filtered flashlights were used to facilitate sampling in darkness. On day 5, gilts were driven in an open-bed pick-up for 15 minutes, returned to the animal house and received 20 minutes of boar exposure. Boar exposure was continued on a daily basis throughout the remainder of experimental period. Blood samples were drawn from each gilt until 7 days after expression of estrus or for 12 days for those gilts that did not exhibit estrus. Blood samples were drawn by venipuncture from the ewes during the entire experimental period. Serum concentrations of melatonin were measured in sera following extraction with ethyl ether by radioimmunoassay utilizing Guildhay antisera. For each sampling day within a gilt and ewe, a ratio of serum melatonin during the night and day was determined. Three replications were conducted (10 gilts/rep). Only 65 of 406 bleeding period (16.0%) exhibited a nocturnal rise in serum melatonin. Number of gilts expressing a nocturnal rise in serum melatonin did not differ as gilts approached puberty (P>.05). Incidence of nocturnal rises of melatonin were similar (P>.05) in gilts that attained puberty and those that did not attain puberty. Majority of the bleeding periods in ewes (85.1%) demonstrated nocturnal rises in melatonin throughout the experiment. These data indicate clearly that nocturnal rises in serum melatonin are not necessary for a gilt to attain puberty.
Key Words: Gilt, Puberty, Melatonin
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