Effects of heat damage and crystalline amino acid supplementation on growth performance of weanling pigs fed diets based on soybean meal and enzyme-treated soybean meal

An experiment was conducted to test the hypothesis that growth performance of weanling pigs can be predicted from the concentration of reactive Lys in heat-damaged soybean ingredients and that supplementation with crystalline amino acids (AA) can compensate for reduced reactive Lys. One source of conventional soybean meal (SBM) and one source of enzyme-treated soybean meal (ESBM) were each divided into three batches. One batch of SBM and one batch of ESBM were used without further processing, one batch of SBM and one batch of ESBM were autoclaved at 120 ± 1°C to moderately heat-damage the ingredients and reduce reactive Lys to 85% of total Lys in each ingredient. The last batch of SBM and ESBM were autoclaved at 120 ± 1°C to severely heat-damage the ingredients and reduce reactive Lys to approximately 70% of total Lys. Four diets were formulated for phase 1 (days 0 to 14 post-weaning) and four additional diets were formulated for phase 2 (days 15 to 28 post-weaning). The four diets in each phase included a control diet containing the non-autoclaved SBM and ESBM, a diet containing moderately heat-damaged SBM and ESBM, a diet containing severely heat-damaged SBM and ESBM, and a diet containing severely heat-damaged SBM and ESBM supplemented with crystalline AA to match digestible AA levels in the control diet. A total of 160 weanling pigs with an initial body weight (BW) of 5.71 ± 0.55 kg were allotted to the 4 treatments in a randomized complete block design with 10 replicate pens per treatment. Growth performance and feed intake were recorded over 28 days. Results indicated that autoclaving reduced reactive Lys, Lys-to-crude protein ratio, sucrose, stachyose, and raffinose, whereas glucose and fructose increased as autoclaving time increased. Pigs fed severely heat-damaged diets had reduced final BW and average daily gain (ADG) compared with pigs fed the control diet (P < 0.001). Supplementation with crystalline AA partially restored growth performance of pigs, but pigs fed the AA supplemented diet had reduced (P < 0.05) ADG and final BW compared with pigs fed the control diet. Reactive Lys intake was strongly correlated (P < 0.001) with final BW and ADG. In conclusion, heat-damage of soybean ingredients reduces reactive Lys and growth performance of pigs, but supplementation with crystalline Lys, Met, and Thr can partially compensate for the loss of nutritional value. • Autoclaving soybean meal reduced total lysine and reactive lysine • Diets containing heat damaged soybean meal reduced final body weight of pigs • Crystalline amino acids supplementation partially restored growth of pigs • Reactive Lys intake of pigs can predict average daily gain and final body