Effect of supplemental lighting on puberty, follicular development, pituitary and serum concentrations of LH and hypothalamic content of GnRH in gilts

Abstract

ABSTRACTOne hundred and thirty crossbred gilts (Yorkshire × Duroc × Hampshire) were exposed to either natural (40 lux) or supplemental lighting (700 lux) beginning at 8 weeks of age. Gilts received supplemental lighting from 40-W flourescent bulbs from 05·15 to 09·00 h and 16·30 to 20·15 h from 9 September to 22 April. At 4 months of age, all gilts were exposed daily for 15 min to mature boars five times weekly. Twelve gilts from each group were slaughtered at 4, 5, 6 and 7 months of age. All gilts were bled from indwelling cannulas at 20-min intervals for 4 h the day preceding slaughter. In addition, blood samples were drawn weekly from 17 gilts in each group from 7 to 9 months of age and analysed for progesterone to determine age of puberty. Twelve of 17 gilts that received supplemental lighting reached puberty at 228 (s.e. 11) days of age whereas 11 of 16 gilts that received natural lighting reached puberty at 252 (s.e. 7) days of age (P = 0·07). No significant differences occurred in anterior pituitary gland weight or pituitary concentration of LH, mean concentrations of serum LH or number of LH secretory spikes between natural and supplemental-lighted gilts at each month (all P > 005). Concentration of oestradiol-17β and progesterone in follicular fluid was similar between treatment groups within months and follicular size (P > 0·05). Content of GnRH in the stalk-median eminence, preoptic area and hypothalamus proper were also similar between treatment groups (P > 0·05). In summary, supplemental lighting reduced the age of puberty in gilts without a detectable change in pituitary, hypothalamic or ovarian parameters.