Amino acid digestibility of plant protein feed ingredients for growing pigs

Two experiments were designed to determine the N and AA digestibility of various protein sources (potato protein concentrate, soy protein concentrate, soy protein isolate, linseed meal, sunflower meal, cottonseed meal, canola meal, and camelina meal) fed to growing pigs. In each experiment, barrows were surgically fitted with a simple T-cannula at the distal ileum and fed 4 experimental diets and a N-free diet (NFD) on the basis of a replicated 5 × 2 crossover arrangement with 5 diets and 2 periods. For Exp. 1, 20 cannulated 25-kg barrows received potato concentrate, soy concentrate, soy isolate, and linseed meal. The apparent ileal digestibility (AID) and standardized ileal digestibility (SID) of N for potato concentrate, soy concentrate, and soy isolate were similar and greater than that for linseed meal ( < 0.05). The AID and SID of Leu and Thr were greater in potato protein concentrate than soy concentrate ( < 0.05), and AID and SID of Thr were lower in soy isolate than potato concentrate. The AID and SID of all essential AA were similar between soy isolate and soy concentrate. Linseed meal had the lowest AID and SID of N and AA digestibility among protein sources ( < 0.05). In Exp. 2, sunflower meal, cottonseed meal, canola meal, and camelina meal were fed to 42-kg barrows to determine their AID and SID of AA. The AID and SID of N and all AA were greatest for sunflower meal ( < 0.05), and canola meal had similar AID and SID of N, Met, Thr, Leu, and Val. The AID and SID of all essential AA, except for Met and Trp, were lowest for sunflower meal ( < 0.05). Cottonseed meal had lower AID and SID for Lys, Ile, Leu, Met, Thr, and Val compared with the other protein sources ( < 0.05). In conclusion, the digestibility of N and AA varies greatly among oilseed meals.