METABOLIC AND ENDOCRINE CHANGES ASSOCIATED WITH UNDERNUTRITION IN THE PERIPUBERTAL GILT

The effect of feed restriction on circulating metabolites and metabolic and gonadotropic hormones was determined in Large White gilts. From 25 kg BW and 80 d of age, control gilts (CTRL, n = 10) were fed close to ad libitum intake, whereas restricted-fed gilts (REST, n = 10) were offered approximately 50% of the CTRL diet. Estrus was detected with a mature boar. Serial blood samples were collected at approximately 160 and 210 d of age from 0800 to 2000. A meal was supplied at 0900, and an i.v. injection of GnRH (80 ng/kg BW) was given at 1600. The gilts were slaughtered at 220 d of age. No REST and four CTRL gilts exhibited their first estrus between the two series of blood samplings. Feed intake, daily gain, and fat content of the carcass were reduced by 50% in REST gilts (P < .001). Preprandial concentrations of free fatty acids were significantly lower in CTRL gilts at 210 d of age than at 160 d and than in REST gilts at both ages. Within the CTRL group, concentrations were lower (P < .05) at both ages in gilts pubertal before 210 d than in others. After the meal, plasma insulin and urea increased in all gilts, whereas glucose increased and free fatty acids decreased in all except the 210-d CTRL gilts. The afternoon concentration of cortisol was slightly higher (P = .09) in REST than in CTRL gilts. The number of pulses and mean and interpulse concentrations of growth hormone did not show any clear variation with feed level and age. Before injection of GnRH, plasma FSH decreased with age in CTRL gilts, whereas basal LH increased with age in all gilts, and the number of LH pulses increased with feed level (P < .05). Within the CTRL group, the number of LH pulses was significantly higher in gilts that were pubertal before 210 d than in others. The highest gonadotropin concentrations after GnRH were detected in REST gilts at 160 d of age. In conclusion, this experiment shows that the time needed for the transition from a fed to an unfed state after the withholding of feed increased during growth of the gilt. This change seems to be associated with pubertal maturation and variations in LH secretion.