EFFECT OF PROTEIN AND LYSINE SUPPLY ON PERFORMANCE, NITROGEN-BALANCE,AND BODY-COMPOSITION CHANGES OF SOWS DURING LACTATION

Using 73 Large White gilts, we studied the lysine requirement during l actation. Sow and pig performance and nitrogen balance of sows were me asured during the total 21-d lactation period. Variation in body compo sition of sows between farrowing and weaning was determined by the com parative slaughter technique. Two levels of crude protein (15.5 and 17 .1%) were combined with two levels of L-lysine HCl supplementation (0 and .16%), resulting in four diets termed P1L1, P1L2, P2L2, and P2L3, containing .66,.77,.77, and .87% crude lysine, and 15.5, 15.5, 17.1, a nd 17.1% crude protein, respectively. Sows' feed intake, litter growth rate, and milk energy and protein output were not affected by the die t. Nitrogen balance over the total lactation increased (P <.001) with an increase in lysine and(or) protein (-11.7, -7.0, -3.4, and .4 g N/d for P1L1, P1L2, P2L2, and P2L3 diets, respectively). The losses of bo dy weight and muscle weight were higher in P1L1 gilts (P <.01 and .05, respectively) than in gilts on other treatments, whereas the loss of adipose tissue and backfat was similar for the four groups. Multiple l inear relationships between lysine intake and milk nitrogen output as predictors and nitrogen balance (N balance = -15.8 + 1.22 lysine -.63 N milk, R-2 =.89) or variation of muscle weight (Vm = -477 + 30.1 lysi ne -14.7 N milk, R-2 =.70) as predicted values were calculated to esti mate lysine requirement according to production performance of sows. C alculations show that for achieving a zero protein balance, 45 to 55 g /d of crude lysine are required for normal to high-yielding sows, resp ectively.