Influence of feed restriction during lactation on gonadotropic hormones and ovarian development in primiparous sows.

Effects of nutritional deficit during lactation on secretion of gonadotropic hormones and ovarian follicular populations around weaning were investigated in 24 primiparous crossbred sows. Sows were allocated to receive close to ad libitum intakes (H) or approximately 50% of this amount (L) during a 28-d lactation. Serial blood samples were collected 1 d before weaning (W-1), in the hours following weaning (W), and 1 d after (W+1). Their ovaries were removed on the day of weaning or 2 d later (W+2) and subjected to macroscopic and histological observations. Mean and basal LH concentrations were not influenced by the level of feeding. Frequency of LH pulses was reduced in L sows (.17, .5, and .5 vs 1.50, 1.17, and .83 pulses/6 h at d W-1, W, and W+1 respectively; P < .05). Mean and basal concentrations of LH were influenced by the day of sampling, being significantly increased within hours following weaning. Mean FSH concentrations were influenced neither by the level of feeding nor by the day of sampling. At weaning, the ovaries from L sows were lighter and had smaller follicles and fewer follicles > or = 4 mm (P < .05). Values of these macroscopic characteristics increased after weaning ( P < .05). At weaning, the percentage of healthy follicles was higher in the first class (< 1 mm) and lower in the second class (1 to 2.99 mm) in L compared to H sows (P < .05). Whatever the day of sampling, IGF-I concentrations in follicular fluid tended to be lower in L than in H sows. These results indicate that feed restriction during lactation inhibits LH pulsatility and ovarian activity.