This study was performed to investigate the weaning-to-estrus interval (WEI) in primiparous and multiparous sows in relation to their weight and back-fat thickness changes and serum hormone imbalance (insulin, growth hormone, and cortisol) at the end of gestation and during lactation. Ten primiparous and ten multiparous Camborough sows, fourth to seventh parity, were used in this experiment. During gestation, daily food intake was 2.4 kg (sow commercial diet: 2.96 Mcal/kg, 16% crude protein) and during lactation all sows were fed on a wet commercial diet (3.34 Mcal/kg, 17%, crude protein) ad libitum three times per day. Blood samples were collected and back-fat thickness at the Pt site were recorded at 6 days before and 2, 7, 14, 21 and 25 days after farrowing. Body weight was recorded on the same dates, except the date before farrowing. The WEI was also recorded. The average daily feed intake was different (P < 0.05) between primiparous and multiparous sows during lactation (5.23 versus 5.72 kg per day, respectively). There was a difference (P < 0.05) between primiparous and multiparous sows in total percentage of back-fat thickness loss from the end of gestation until weaning (-20.18 and -9.03%. respectively). The total percentage of weight loss during lactation was slightly greater(P < 0.05) in multiparous than primiparous sows. Weaning-to-estrus interval was greater (P < 0.05) in the primiparous group when compared with the multiparous group (5.55 and 4.21 days, respectively). No differences were found in insulin, growth hormone (GH), and cortisol concentrations between parity groups, except on the 21st day of lactation. when GH was greater in primiparous sows. There was no correlation between percentage of total weight loss and WEI, or percentage of back-fat thickness loss (total or by periods) and WEI. There were positive correlations between GH serum concentration on the 14th and 21st days and the percentage of weight loss in the third week of lactation (r = 0.46, P < 0.04 and r = 0.52, P < 0.03, respectively). and between GH concentration on the 21st and on weaning days and WEI (r = 0.54, P < 0.02 and r = 0.42. P < 0.06, respectively). Our results indicate that the hormone change (imbalance) during lactation, mainly CHI seems to be a better parameter to explain the difference in WEI between primiparous and multiparous sows than change in body condition. (C) 2001 Elsevier Science B.V. All rights reserved.
