Serum concentrations of melatonin in pigs exposed to various photoperiodic conditions

Michael Lee Green, Purdue University

Abstract

Artificial light has profound effects on the reproductive performance of domestic pigs, but the mechanism by which photic information is transduced is not known. Three experiments were conducted to establish a relationship between serum melatonin (MEL) and the daily light-dark cycle in domestic pigs. Experiment 1. In gilts maintained in a constant 10:14 light:dark (L:D) schedule, scotophase (SP) MEL was higher (P $<$.002) than photophase (PP) MEL after 4, 6, 8 and 10 weeks of exposure. In gilts exposed to decreasing SP, SP MEL was higher (P $<$.02) than PP MEL only in the 12:12 and 13:11 L:D. The SP MEL averaged 2.2 and 2.8-fold greater than the PP MEL in the decreasing and constant SP, respectively. Serum MEL was elevated during SP in 56% of the gilts. Experiment 2. In gilts maintained in a constant 15:9 L:D, serum MEL was higher (P $<$.05) during SP than PP on four of six collection dates. In gilts exposed to increasing SP, a SP elevation (P $<$.05) was present in five different L:D schedules. The SP MEL averaged 2.5 and 3-fold greater than PP MEL in the increasing and constant SP, respectively. Serum MEL was elevated during SP in 57% of the gilts. Experiment 3. Sixty barrows and 120 gilts were exposed to the natural transitions of light from May-Sept. At 3, 4, 5 and 6 months of age, pigs were venipunctured once each during PP and SP. Mean serum MEL was higher (P $<$.0001) during SP than PP, but was similar (P =.85) between gilts and barrows. Only 30% of the pigs had a twofold nocturnal rise in serum MEL. In summary, the domestic pig exhibits an inherently "weak" nocturnal rise in serum MEL, but it is only evident in about one-half of the pigs. The magnitude of the nocturnal rise is not as robust as that in other species and this coupled with the dramatic pig-to-pig variation dampens the ability to detect differences between day and night concentrations of serum MEL. Furthermore, nocturnal rises in serum MEL were detected in short, equatorial and long photoperiods thereby refuting the concept of a critical photoperiod for the rhythm to occur. Also, the direction of change in photoperiod does not influence MEL secretory patterns since nocturnal increases in serum MEL were detected in similar L:D schedules with opposing photoperiod histories.

Degree

Ph.D.

Advisors

Diekman, Purdue University.

Subject Area

Anatomy & physiology|Animals

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