Influence of supplemental lighting during increasing daylength on libido and reproductive hormones in prepubertal boars.

Littermate crossbred boars received either natural lighting or supplemental lighting (incandescent or fluorescent) from 15 to 32 wk of age in two separate experiments. Boars in control and treatment groups received natural daylight through windows of a growing and finishing house from December to April (Exp. 1) or from March to August (Exp. 2). Boars in the treatment groups received supplemental lighting from 0520 to 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 between control and treatment groups. In Exp. 1, boars that received supplemental lighting had higher (P<.05) libido scores at 23, 26, 28, 29 and 32 wk of age. In Exp. 2, boars that received supplemental lighting had higher libido scores at 25, 26, 27, 29 and 31 wk of age. In Exp. 1, mean luteinizing hormone (LH) and follicle stimulating hormone (FSH) concentrations in serum were similar for all treatment groups except that serum LH was higher (P<.05) at 17 wk of age in boars given supplemental light. There was no effect of supplemental light on serum LH or FSH concentrations in the second experiment. Serum concentrations of testosterone were higher (P<.05) at 23 and 25 wk of age and serum androstenedione was higher (P<.05) at 19, 23