Utilization of different soy products as affected by age in chicks

Two experiments were conducted to evaluate the utilization of several different soy products at different ages in New Hampshire x Columbian male chicks. Six pens of eight chicks were fed dextrose-protein source diets (23% CP) containing 1 of 10 different protein sources from 0 to 21 d of age. Excreta were collected at 0 to 2, 3 to 4, 7, 14, and 21 d of age, and AME_n and amino acid (AA) digestibility were determined using acid-insoluble ash as a marker. Protein sources evaluated were as follows: Experiment 1 - casein, soybean meal (SBM), soy protein concentrate (SPC), and soy protein isolate (SPI); Experiment 2 - raw soyflakes, SBM, Williams 82 soybeans, heated Williams 82 soybeans, Kunitz-free soybeans (reduced trypsin inhibitor), lectin-free soybeans, and Kunitz/lectin-free soybeans. In Experiment 1, when comparing the ME_n and AA digestibility values among diets at the same age, the ranking (from highest to lowest) for the four diets was casein, SPI, SPC, SBM. The ME_n values increased (P < 0.05) with age for all four diets, with the increase being much smaller for the casein diet (3%) than the soy diets (mean increase of 13%). In Experiment 2, the SBM diet yielded the highest (P < 0.05) growth performance, ME_n, and AA digestibility values. The ME_n and AA digestibility values of the Williams 82 soybeans, Kunitz-free soybeans, and lectin-free soybeans diets were much lower than those for the SBM diet. In general, the Kunitz/lectin-free soybeans yielded higher growth performance and ME_n values than the Williams 82 soybeans, Kunitz-free soybeans, and lectin-free soybeans. The ME_n values increased with age for most diets, and AA digestibility increased with age for the soy flake and Kunitz/ lectin-free soybean diets. Our results suggest there may be some potential benefits of feeding SPC or SPI during the first 1 to 3 wk posthatching and that underprocessed (under heated) soybeans should not be included in the diets of very young chicks.