Two experiments were conducted to determine the standardized ileal digestibility (SID) of amino acids (AA) and the concentration of metabolizable energy (ME) in soy protein concentrate (SPC) ground to three particle sizes and in soybean meal and fish meal when fed to weanling pigs. An additional experiment was conducted to determine effects of including SPC in diets on growth performance when fed to weanling pigs.

In the first experiment, 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 weanling barrows weighing about 13kg that had a T-cannula installed in the ileum. In the second experiment, 36 barrows weighting about 13.7kg were allotted to a corn-based diet or diets containing corn and soybean meal, fish meal, or SPC ground to the three particle sizes. In the third experiment, 160 pigs weighing about 7 kg were allotted to 4 dietary treatments and 8 pens per treatment with 5 pigs per pen. Diets 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 indicated that the SID of lysine tended to be greater in SPC ground to 180 μm than in soybean meal and that the SID of arginine and tryptophan were greater (P ‹ 0.05) in SPC ground to 70 or 180 μm than in SPC ground to 700 μm. There were no differences in the ME among corn, soybean meal, fish meal, and SPC. The ME of SPC ground to 70, 180, or 700 μm was 3,683, 3,903, and 3,886 kcal/kg DM, respectively. Substitution of spray dried plasma protein and fish meal by SPC ground to 180 μm in diets had no effect on pig growth performance. The researchers concluded that reducing the particle size of SPC may improve digestibility of some indispensable AA but did not affect concentration of ME.