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Photoinduction of Puberty in Boars during Naturally Occurring Short Day Lengths¹

Purdue University, West Lafayette, IN 47907

Abstract

Nine pairs of littermate boars were used to study effects of artificial lengthening of photoperiod on onset of puberty. The control group was exposed to natural daylight (9.3 to 12.7 hr) through windows in a growing and finishing house from October to April. Those in the lighted group received supplemental light in the morning and evening for a total photoperiod of 15 hours. There was no difference in body weight between boars in the two groups for the first 5 months of age. However, at 24 weeks of age, those in the lighted group were heavier (P<.05). Feed intake was reduced at 25 weeks of age, and the difference in body weight gradually disappeared thereafter. Testicular firmness decreased with age, and testes of the treated animals were less firm from 24 to 30 weeks of age. There was no difference in testicular volume between the two groups. At 8 months of age, semen had been collected from only 55.5% of the control boars, but had been collected from all boars exposed to supplemental light. Of the boars collected, there was no difference between treatments in sperm concentration, sperm-rich fraction volume, total ejaculate volume, percentage progessively motile sperm or percentage abnormal sperm either by collection interval or by ejaculate number. Overall sperm concentration and total viable sperm were greater (P<.01) for boars receiving supplemental lighting. No increase in numbers or types of abnormal sperm was observed with photoperiod stimulation.

¹ Journal Paper No. 7297 of the Purdue Agricultural Experiment Station, Department of Animal Sciences.

² Present address: Department of Animal Science, Macdonald College of McGill University, Ste Anne de Bellevue, Quebec CA H0A 1CO.

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