Emma Clowes, Frank Aherne, and Roy Kirkwood

 Alberta Pork Research Centre, 410 Agriculture/Forestry Centre, University of Alberta, Edmonton, AB, T6E 2P5, CANADA

 At least 60% of a sows annual feed intake is consumed during gestation. Therefore, overfeeding gestating sows can significantly influence feed costs per pig weaned, and increase nitrogen and phosphorus excretion with the potential for ground water pollution. Currently, sows are fed a single diet at a fixed daily feed allowance in gestation. However, sow body weight increases during gestation and while the developing litter has negligible growth in the first trimester, it increases exponentially in the third. This feeding system therefore may overfeed animals in early gestation and underfeed them in late gestation, leaving them in a poor metabolic state to enter lactation and predisposing the animal to a poor reproductive performance upon weaning. A feeding regimen that more closely matches the protein requirement of gestating sows in each trimester of gestation would be more appropriate. We achieved this by feeding 25 gilts a 12, 13, and 16% CP diet in trimester 1, 2 and 3, respectively (Phase-fed) and compared these animals to a further 25 gilts which were fed a single diet (14% CP) over gestation (Control). Both treatments were continued over three successive parities. Sows were weighed and backfat measured at breeding, at the end of each trimester (d 38, 74 and 109 of gestation), at farrowing, d 10 and 20 of lactation, and weaning, and litters were weighed weekly. Nitrogen balance studies were conducted in the first gestation, at the end of each trimester in a subset of 6 gilts per treatment.