Lack of a nocturnal rise in serum concentrations of melatonin preceding puberty in gilts

Purdue University 1996 Swine Research Report. Photoperiodism has been studied extensively in many mammals. It has been linked to reproduction in seasonal breeders such as sheep, horses, hamsters, ferrets, deer, and mink. The cue that seasonally breeding animals must receive to initiate or continue reproduction activity is received by the eye. This message is transferred from the eye to the pineal gland, the internal clock that regulates the synthesis and release of the hormone melatonin. The relationship between melatonin secretion and seasonality has been studied to some extent in pigs but much of the evidence is conflicting. Researchers in Australia report that “in pigs, as in other species, the concentration of melatonin in plasma increases in the dark and the duration of the nocturnal increase depends on photoperiod.” In 1993, our laboratory demonstrated that only 30% of 3, 4, 5, and 6 month old prepubertal (non-cycling) gilts showed a 2-fold increase in melatonin during darkness. From these data, Mike Green determined that “the small nocturnal elevation coupled with the highly variable response suggests the lack of a timekeeping role for melatonin in the domestic pig.” The objective of the study reported here was to determine if a nocturnal rise in serum melatonin was necessary before a gilt can attain puberty.