Effect of weaning-to-conception interval and lactation length on subsequent litter size in sows

A retrospective study of the effects of weaning-to-conception interval (WCI), lactation length and their interaction with selected factors on subsequent litter size has been performed on sows born in 1990 in the French herd. Results from 1881 herds and 46,523 sows were analysed. Sows raised outdoors weaned significantly fewer piglets than those raised indoors. The effects of lactation length, breed, parity, age at first service and WCI on litter size were studied on animals raised indoors. Repeatabilities of litter size and WCI were low, and comprised between 0.20-0.24 and 0.11-0.15, respectively. Sows conceiving within 5 days after weaning farrowed larger litters, whereas litter size decreased when animals were bred on days 6 to 10. Late first-mated gilts has a larger second litter. However, the decrease in subsequent second litter size due to increase in WCI interval was similar for sows in different 'age at first service' classes. The effect of WCI on subsequent Litter size was more pronounced in pure Landrace than in Large-White or crossbred sows, and in parity 2 than in further parities. Two optimal values for both litter size and WCI were observed for weaning, at either 21 or 28 days. Results indicated that management policies, and particularly lactation length, played a major role on sow performance. (C) 1997 Elsevier Science B.V.