Efficacy of dried whey and its lactalbumin and lactose components at two dietary lysine levels on postweaning pig performance and nitrogen balance.

Two experiments were conducted to determine the efficacy of lactalbumin and lactose components of dried whey on gain and feed performance responses and N retention of weanling swine. In Exp. 1, a 2 X 5 factorial arrangement of treatments in a randomized complete block design in seven replicates was used to evaluate the efficacy of two dietary lysine levels (.90 and 1.30%) in 1) a corn-soybean meal (C-SBM) mixture, 2) C-SBM and 20% dried whey (C-SBM-DW), or the dried whey component replaced with 3) lactalbumin and cornstarch, 4) lactose and an amino acid mixture, or 5) the combination of lactalbumin and lactose. A total of 420 pigs weaned at 23 +/- 2 d of age, weighing an average of 6.8 kg BW, were used in a 3-wk experiment. Experiment 2 was a balance trial conducted as a 3 X 2 X 3 factorial arrangement in a split-plot design in three replicates. The negative (i.e., C-SBM) and positive (i.e., C-SBM-DW) control diets and the C-SBM-lactalbumin-cornstarch diets at the two lysine levels of Exp. 1 were the main plots, each evaluated for a 3-wk postweaning period. Growth rate (P < 0.05), feed intake (P <0.01), N retention (P <0.01), and apparent N digestibility (P <0.05) were increased when pigs were fed the C-SBM-DW compared with the C-SBM diet. The replacement of dried whey with lactalbumin and cornstarch resulted in lower growth (P <0.05), feed intake (P <0.10), and N retention (P <0.05) compared with the C-SBM-DW but gains and feed intakes similar to those of pigs fed C-SBM diet. Replacing dried whey with lactose and the amino acid mixture resulted in a higher growth rate (P <0.05) and improved gain-to-feed ratio (P <0.05) relative to the C-SBM-DW diets. The 0.90% lysine level in the C-SBM and C-SBM-DW diets resulted in poorer gains (P <0.05) and feed intakes (P <0.05) compared with the 1.30% lysine level, but not when lactose and(or) lactalbumin and lactose replaced the dried whey component. These results suggest that the lactose component of dried whey is the primary cause of improved gain and feed intake responses when dried whey is added to pig starter diets.