Determination of the optimal dietary threonine:lysine ratio for finishing pigs using three different methods

The effect of dietary threonine:lysine (thr:lys) ratio for finishing crossbred pigs was investigated on the basis of three different methods, i.e., the concentration of plasma urea nitrogen (PUN) (I), a performance experiment (II) and a nitrogen-balance study (III). In all three experiments, two feeding levels and four different dietary thr:lys ratios, based on standardised ileal digestibility, were used. In experiments I and II, the thr:lys ratios were 0.58, 0.62, 0.66 and 0.70, respectively, while in experiment III, the thr:lys was extended, i.e., ratios 0.58, 0.64, 0.70 and 0.76, respectively. In all three experiments, the pigs were fed three times/day. The diets were based on wheat, barley and soybean meal. In experiment I a dietary thr:lys ratio of 0.66 tended to be optimal. The optimal dietary thr:lys ratio was not influenced by growth rate, but was found to increase with the live weight. Based on the numerical differences between thr:lys ratios the optimal dietary thr:lys ratio was found to be 0.62 and 0.64, in experiments II and III, respectively. Based on the present studies it is concluded that the optimal thr:lys ratio is about 0.64 for finishing pigs. (C) 2003 Elsevier B.V. All rights reserved.