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Growth trials with weaned pigs (28 d old and 7.5 kg initially) and growing-finishing pigs (19 to 97 kg), plus a digestion trial were conducted to evaluate the nutritional value of commercially processed glandless cottonseed meal (GCSM). The GCSM contained 43% protein, 15.5% fiber, 1.62% lysine and .038% total gossypol. In the growth trials, GCSM was substituted in 20% increments for 0 to 100% of the supplemental protein in corn-soybean meal-based diets. Crystalline lysine was added to all GCSM diets to make them isolysine with the control corn-soybean meal diets. Increasing increments of GCSM resulted in linear reductions (P<.01, P<.05 or P<.10) in daily gain and linear increases (P<.01, P<.01 and P<.05) in feed/gain for pigs during the starter, grower and finisher trials, respectively. However, examination of the data indicated similar performance for pigs fed 0 to 40% supplemental GCSM protein, and only at the 60 to 100% levels was performance substantially reduced. Results from all growth trials indicated that GCSM plus lysine can be used to replace at least 40% of the supplemental protein in corn-soybean meal-based diets without affecting performance. Results of the digestion trial indicated similar or greater digestibilities of N and all essential amino acids for GCSM than soybean meal when measured at the end of the small intestine. The one exception was lower (P<.01) lysine digestibility (77.4 vs 84.0%) for GCSM. Estimated digestible lysine contents were similar for the soybean meal control diets and GCSM-containing diets of the growth trials, suggesting that some other factor was responsible for the lowered performance at the higher levels of GCSM.

Eight digestion trials were conducted with pigs fitted with ileal T-cannulas to determine the apparent digestibilities of N and amino acids in common protein feedstuffs. Trial-to-trial variation was minimal as determined by the variation in digestibilities for soybean meal, which was evaluated in each trial. Apparent digestibilities varied widely; ileal N digestibility ranged from 88 to 63%, and ileal lysine digestibility ranged from 93 to 40%. In general, ring-dried blood meal, corn gluten meal, Menhaden fish meal, poultry-by-product meal and extruded whole soybeans were the most digestible, followed by canola meal, sunflower meal, peanut meal and meat and bone meal. Cottonseed meal and feather meal were the least digestible. Mean values for each feedstuff agree well with published data. Variation in digestibilities among samples of the same feedstuff was greatest for the meat and bone meals. Regression of ileal essential amino acid digestibilities on ileal and fecal N digestibility indicated that amino acid digestibilities can be predicted more precisely from ileal N digestibility than from fecal N digestibility. However, neither ileal nor fecal N digestibility could be used with a high degree of certainty to predict ileal amino acid digestibilities.