Nutritional value of soy protein concentrate ground to different particle sizes and fed to pigs

Two experiments were conducted to determine the standardized ileal digestibility (SID) of CP and AA and concentrations of DE and ME in soy protein concentrate (SPC) ground to 3 particle sizes and in soybean meal and fish meal when fed to weanling pigs. An additional experiment was conducted to determine effects on growth performance and blood characteristics of including SPC in diets fed to weanling pigs. In Exp. 1, a N-free diet and diets containing soybean meal, fish meal, or SPC ground to a mean particle size of 70, 180, or 700 μm as the only source of AA were fed to 6 barrows (initial BW: 12.90 ± 1.51 kg) that had a T-cannula installed in the distal ileum. In Exp. 2, 36 barrows (13.70 ± 1.86 kg BW) were allotted to a randomized complete block design with 6 diets and 6 replicate pigs per diet. A corn-based diet and diets containing corn and soybean meal, fish meal, or SPC ground to the 3 particle sizes were used. In Exp. 3, 160 pigs (initial BW: 7.06 ± 1.07 kg) were allotted to 4 dietary treatments with 8 pens per treatment and 5 pigs per pen. Pigs were fed one of 4 diets during phase 1 (d 0 to 14 postweaning), and a common diet in phase 2 (d 14 to 28 postweaning). The 4 diets used in phase 1 included a control diet containing fish meal and spray-dried plasma protein, and diets in which fish meal, spray-dried plasma protein, or both fish meal and spray-dried plasma protein were replaced by SPC ground to 180 μm. Results of Exp. 1 indicated that the SID of His, Lys, and Thr tended (P < 0.10) to be greater in SPC ground to 180 μm than in soybean meal, and the SID of Arg, Ile, Phe, and Trp was greater (P < 0.05) in SPC ground to 70 or 180 μm than in soybean meal. There were no differences in the DE and ME (DM-basis) among corn, soybean meal, fish meal, and SPC ground to 70, 180, or 700 μm. Results of Exp. 3 indicated that growth performance of pigs fed the 4 experimental diets in phase 1 was not different in phase 1, phase 2, or in the entire experiment. In conclusion, grinding SPC to approximately 180 μm maximizes SID of indispensable AA without impacting ME and diets based on soybean meal and SPC as the main protein sources may be fed to pigs during the initial 2 wk postweaning without affecting growth performance.