Relationship between lactation-associated body weight loss, levels of metabolic and reproductive hormones and weaning-to-oestrous interval in primiparous sows.

Twelve conventionally fed primiparous sows with a similar number of piglets were divided into 3 groups (n = 4) according to their body weight loss after a 5-week lactation as follows: H-gr (loss greater than 25 kg), M-gr (loss 11-25 kg) and L-gr (loss less than or equal to 10 kg). Blood samples were collected at 9, 12, 15, 18 and 21 h, from 4 days before weaning until 3 days afterwards, and every 15 min for 6 h on the day before and the day after weaning. The group of sows with higher weight loss during lactation tended to have a higher farrowing weight and higher pre-weaning plasma prolactin levels. At weaning, the L-gr sows had higher plasma insulin and lower plasma cortisol concentrations, especially when compared with H-gr sows. Among the ten sows that showed oestrus within 10 days of weaning, no between-group differences were found in the length of the interval from weaning to oestrus. No significant differences between groups were observed in levels of oestradiol-17 beta and LH. The higher level of insulin in L-gr sows might relate to the higher number of corpora lutea observed in this group.