Innate variability in sexual development irrespective of body fatness in gilts1

Abstract

To separate the effects of fatness from those of lean tissue growth on reproductive development, 52 gilts (33.2 kg, 75 d) had ad libitum access to a high-energy diet (HE; n = 31) or were fed restrictively a low-energy diet (approximately 80% of ad libitum; LE; n = 31) until 160 d of age. All HE and 15 LE gilts were then slaughtered; the 16 LE gilts that remained were then allowed ad libitum access to the low-energy diet until slaughter at 175 d (LER). Twelve littermate trios allocated across treatments were cannulated and bled during both unfed and fed states before slaughter. Gilts in the HE group were 8 kg heavier, 3.5 mm fatter (backfat), and consumed 14.9 MJ of DE more per day than gilts in the LE group at 160 d (hereafter P < .05); LER gilts were 7 kg heavier, 2.2 mm fatter, and consumed 21 MJ of DE more per day at 175 d than LE gilts at 160 d. Carcass fat was lower in LE gilts than in HE or LER gilts, but carcass lean was similar among groups. Treatment did not affect basal or episodic LH or growth hormone secretion, reproductive tract weight, follicular volume, or plasma or follicular fluid estradiol-17 beta. Postprandial plasma insulin was greater in LER than in HE or LE gilts, but plasma insulin-like growth factor I and urea nitrogen were similar among groups. Plasma nonesterified fatty acids and creatinine were greater in HE than in LE or LER gilts. These results suggest that when protein accretion rate is maximal, differences in fatness do not influence reproductive development in the prepubertal gilt. Irrespective of treatment, the only measured factor showing an association with ovarian development was the innate variability in episodic and basal LH secretion.