Littermate pairs of crossbred boars, barrows and gilts were used to study the effects of an artificially extended photoperiod during decreasing daylength on puberty in boars and on weight gain and feed efficiency. Libido scores of the boars exposed to the extended photoperiod were higher (P < .01) than those of controls at 24 and 26 weeks of age. At 26 weeks of age, semen had been collected from 74% of the boars on supplemental light but from only 26% of the controls. Lighting treatment did not affect semen quality. The number of ejaculates previously collected did affect semen quality. Motility and total sperm per ejaculate increased with increasing ejaculate number, while the percentage of abnormalities appeared to decrease. A second group of boars was delayed in the development of mating behavior, perhaps because of inadvertent consumption of Gibberella zeae-infected corn. The extended photoperiod did not exert a beneficial effect on weight gain or feed efficiency of boars, barrows or gilts.