THE EFFECT OF A 15-H PHOTOPERIOD ON REPRODUCTIVE FUNCTION IN BOARS AT 2, 3, 4 OR 5 MONTHS OF AGE

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Abstract
The effects of supplemental lighting in stimulating reproductive function in prepuberal boars were studied using littermate boars divided equally into four groups (n = 9). All boars received natural daylight (9.2–12.8 h) until 2 mo of age, followed by artificial light given daily according to the following schedule: boars were exposed to a 15-h photoperiod beginning at the age of 2 (group I); 3 (group II); 4 (group III) or 5 mo (group IV). Libido scores of the four groups increased with age (P < 0.001). Seminal plasma protein (P < 0.01) and zinc concentration (P < 0.05), sperm-rich concentration, sperm-rich volume, total semen volume and total viable sperm increased (P < 0.05) with age in all four groups. The photoperiod treatment had no effect on semen quality on a per ejaculate basis between the groups; 15 h of light per day was not effective in accelerating the onset of puberty when administered from 2, 3, 4 or 5 mo of age onward.