Influence of supplemental lighting during periods of increasing or decreasing daylength on the onset of puberty in gilts.

Sixty-four crossbred gilts were assigned randomly to one of four treatments at 9 to 11 wk of age: supplemental lighting and boar exposure, supplemental lighting without boar exposure, no supplemental lighting with boar exposure and no supplemental lighting and no boar exposure. Gilts in all treatment groups received natural daylight through windows of a growing and finishing house from February to July (Exp. 1) or from August to January (Exp. 2). Gilts in treatment groups 1 and 2 received supplemental lighting from a 250 w incandescent bulb (300 lx) from 0520 and 0830 h and from 1630 to 2020 h, for a total daily photoperiod of 15 h. No differences in weight gain or feed efficiency were found among any of the treatments. In Exp. 1, the proportion of gilts displaying estrus by 8 mo of age were 77, 13, 79 and 31% for treatments 1, 2, 3 and 4, respectively. As expected, the proportion of gilts that reached puberty was greater (P less than .01) in gilts that had received boar exposure than gilts that did not receive boar exposure. However, supplemental lighting given during periods of increasing natural daylength did not increase (P less than .05) the proportion of pubertal gilts or reduce the age of puberty. In Exp. 2, the proportion of gilts displaying estrus by 8 mo of age were 75, 7, 80 and 12% for treatments 1, 2, 3 and 4, respectively. Boar exposure increased the proportion of gilts reaching puberty by 8 mo of age.(ABSTRACT TRUNCATED AT 250 WORDS)