Effect of bird-resistant and non-bird-resistant sorghum grain on amino acid digestion by beef heifers

The effects of sorghum type on amino acid digestion were determined by feeding heifers (230 kg) equipped with ruminal, duodenal, and ileal cannulas bird-resistant (BR) or non-BR grains that had a normal or waxy endosperm (NORMAL-BR, WAXY-BR, NORMAL, WAXY). Dry-rolled grain diets were fed at 2% of BW in a 4 X 4 Latin square design. Total (TAA), essential (EAA), and nonessential (NAA) amino acid intake (grams/day) tended to be greater for BR than for non-BR grains. Feed (plus endogenous) amino acids reaching the duodenum were calculated by subtracting amino acids of microbial protein from total flow. Flow (grams/day) of total and feed TAA, EAA, NAA, and proline-rich-protein (sum of aspartate, glutamate, glycine, and proline) to the duodenum was greater (P 0.05) for BR than for non-BR grains. The ratio between feed proline-rich-protein and NAA reaching the duodenum was similar to that noted with feed intake. Amino acid disappearance (grams/day) from the small intestine was unchanged (P 0.10) by sorghum type, although the digestibility (percentage of duodenal flow) of TAA, EAA, NAA, and most individual amino acids was decreased (P 0.05) for BR varieties. Amino acid flow to the cecum (grams/day) was generally greater for NORMAL-BR than for WAXY-BR (P 0.10) or for NORMAL (P 0.01) and greater (P 0.10) for WAXY-BR than for WAXY. Condensed tannins in BR sorghum grain seem to decrease small intestinal amino acid digestibility by increasing indigestible feed protein flow to the duodenum, rather than by increasing the supply of endogenous protein or inhibiting digestive enzymes