THE EFFECT OF FOUR DIFFERENT TYPES OF FLUORESCENT LIGHT ON GROWTH, REPRODUCTIVE PERFORMANCE, PINEAL WEIGHT AND RETINAL MORPHOLOGY OF YORKSHIRE GILTS

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Abstract
Fifty-seven, 110-day-old Yorkshire gilts were housed in 16 basement pens to study the effect of four types of fluorescent light upon growth, puberty, ovulation rate, fetal number, fetal sex ratio, pineal weight and the retina. Gilts exposed to red light achieved puberty later (P < 0.01) and at heavier weights (P < 0.05) than gilts exposed to cool white light, full spectrum daylight, or ultraviolet light. Each gilt was exposed to a photoperiod of 16 h of one light source, with 8 h of darkness daily. Average weights and ages at puberty were 104.5, 99.9, 99.7 and 97.7 kg and 192.1, 177.2, 181.5 and 179.9 days, respectively. Heavier pineal glands (P < 0.05) were also observed in the gilts exposed to red light, indicating that a heavier pineal gland may be associated with delayed puberty. In addition, there was a significant trend (P < 0.01) across all treatments for the older animals to have heavier pineal glands at slaughter. Significant differences attributable to the four lighting treatments were not noted in average daily gain or feed efficiency. When the gilts were slaughtered, at not earlier than day 40 of gestation, no significant differences were found in ovulation rate, fetal number and fetal sex ratio between treatments. A histological investigation of the retina from the gilts did not reveal detectable damage due to the ultraviolet light or other light treatments. It is concluded that the gilts were responsive to those regions of the light spectrum below red. Cool white fluorescent light appears to be the most economical fluorescent lighting for maintaining optimum growth and reproductive performance in the breeding herd. Key words: Light spectrum, photoperiod, growth, puberty, pineal gland, retina