Influence of varying intensities of supplemental lighting during decreasing daylengths on puberty in gilts

Abstract

Thirty-two crossbred gilts were randomly assigned to one of four treatments at 84 days of age: (1) supplemental lighting (1200 lux); (2) supplemental lighting (360 lux); (3) natural lighting (90 lux); and (4) reduced lighting (< 10 lux). Gilts received supplemental lighting from 40-W fluorescent bulbs from 05.30 to 08.30 and 16.30 to 20.30 h from 25 September to 1 April. From 120 to 270 days of age, gilts were exposed to mature boars for 15 min daily. The proportion of gilts attaining puberty by 270 days of age was 4 8 , 5 8 , 6 8 and 1 8 for treatment groups 1, 2, 3 and 4, respectively. The number of gilts attaining puberty was less ( P < 0.05) in the reduced lighting treatment than other treatment groups. Mean serum concentrations of LH, number of secretory spikes and magnitude of LH spikes were similar ( P > 0.05) among lighting treatment groups. There were twice as many secretory spikes of LH at 220 days than at 135 days of age but the increase was not related to light intensity. Serum concentrations of PRL were higher ( P = 0.06) at 135 days than 220 days of age, regardless of light treatment. Data from the present experiment indicate that exposure of gilts to reduced lighting (< 10 lux) delays puberty without altering secretory patterns of serum LH or PRL.