THE EFFECTS ON LITTER SIZE OF PREVIOUS LACTATION LENGTH AND PREVIOUS WEANING-TO-CONCEPTION INTERVAL IN ONTARIO SWINE

Lactation length and the weaning-to-conception interval are two key fe atures of reproductive efficiency. A retrospective study of 112 Ontari o swine farms was conducted to determine the association between litte r size and previous lactation lengths up to 40 days and previous weani ng-to-conception intervals up to 14 days. Threshold dummy variables we re created for lactation lengths between 14 days and 40 days and for w eaning-to-conception intervals up to 14 days. The litter size increase d progressively at previous lactation lengths of 20, 25, 27 and 33 day s (P<0.05). Sows bred on Days 2-4 post weaning had essentially the sam e litter size. Litter size decreased progressively for sows bred on Da ys 5, 6, and 7 post weaning and then reached a plateau until it increa sed again for sows bred on Day 11 or later (P<0.05).