Body reserves are important in reproduction because they can be used by the sow to buffer the nutritional stress through a low intake of food in lactation (Mullan and Williams, 1988). Quantitative information on the body composition of first-litter sows during lactation is clearly required to establish what body reserves are mobilized during lactation, and how this relates to subsequent reproductive performance. The aim of this study was to quantify the body reserves of first-litter sows at farrowing and to measure the change in these reserves during lactation.

Animals selected for body composition studies were from the High-High, High-Low, Low-High and Low-Low groups of an experiment described by Mullan and Williams (1988). Animals were selected according to bodyweight, depth of backfat and litter size, with the object to have animals that were representative of those in the earlier experiment. Sows were removed from their litter, weighed and the depth of backfat measured by ultrasound at the P2. Within three hours of weaning animals were slaughtered and the head, trotters, tail, viscera one side of the carcass were frozen, minced and chemically analysed for lipid, protein, water and ash.