Photoperiod, Timed Weaning and Reproductive Performance of Sows

Background and Objectives: Strategies that enhance sow estrus detection and the correct time of mating/insemination are critical to reproductive and economic advancement of individual herds and of the swine industry. The domestic pig, whose ancestors were short-day seasonal breeders, still retains some the responsiveness to photoperiod (daylength) change (Claus & Weiler, 1985; Bassett, 1996). Long photoperiods (14-16h) can be associated with delayed puberty (Paterson & Pearce, 1990) prolonged weaning to estrus interval (WEI), variable duration of estrus and lowered fertility (Claus Weiler, 1985; Prunier et al., 1994). Part of the lowered fertility with longer photoperiods may be associated with variation in WEI and duration of estrus, which makes correct timing of insemination difficult. With time of ovulation occurring at about 70% of the estrus period (Soede & Kemp, 1997), ovulation would be occurring sooner in sows having a shorter estrus than in ones with longer heat periods. This, obviously, complicates breeding management strategies. If the WEI and duration of estrus can be improved or synchronized by manipulation of photoperiod and/or time of weaning, there is much greater likelihood of mating or inseminating at a time conducive to optimum fertility of the sow herd. The result would be higher pregnancy and farrowing rates, fewer non-productive days (NPD) and larger litter sizes arising from semen deposition coinciding with fr &