FACTORS AFFECTING THE WEANING-TO-ESTRUS INTERVAL IN THE SOW

Over a 5-year period, data were collected on a 390 sow pig unit and an alysed for effects on the weaning-to-estrus interval(WOI). The length of WOI was influenced by parity (p<0.001), breed (p<0.001), season (p< 0.001), housing system (p<0.001), number of piglets weaned (p<0.001), reduction of the body weight during lactation (p<0.001), the interacti on between parity and housing system (p<0.001), and the interaction be tween parity and weight loss during lactation (p<0.05). Body-weight lo ss during lactation had a clear effect on WOI in first and second-pari ty sows: over 7.5 % reduction in body weight during the first lactatio n and over 12.5 % during the second lactation prolonged WOI(p<0.05). G roup housing during gestation in a large continuously changing group a lso prolonged WOI in first and second-parity sows (p<0.01). Independen t of parity and weight loss during lactation, WOI was prolonged when t he litter size at weaning exceeded eitht piglets (p<0.05). Also indepe ndent of parity and weight loss during lactation was the effect of sea son: sows weaned in the period from July until September were most lik ely to have prolonged WOI (p<0.01) or to be treated with estrus-induci ng hormones (p<0.05). WOI was also dependent on the genotype of the so w. The use of estrus-inducing hormones masked the effect of factors pr olonging WOI, in the 12.3 % of cases where these hormones were used.