If dietary intake is insufficient to meet the metabolic needs of the sow during lactation then maternal body reserves (body fat and body lean) are mobilised to support milk production. However the extent to which body reserves are mobilised may influence the metabolic and physiological state of the sow and hence reproductive function after weaning (Mullan and Close, 1989). There is little available information on the metabolic response of the lactating sow and the present experiment was designed to study the partition and utilisation of energy and nitrogen (N) intake in sows during their first lactation. This should aid in the understanding of how the dynamics of nutrient utilisation during lactation may influence the metabolic and reproductive state of the sow.

The experiment was designed in a 2 X 2 factorial arrangement (5 animals per treatment) with 2 levels of feed (H, 5.5 kg/d and L, 3.0 kg/d) during lactation and with 2 litter sizes at each feeding level (6 or 12). Sows were accommodated throughout the 21-day lactation in farrowing crates adapted to permit the total collection of sow and piglet excreta.