EFFECT OF BIRD-RESISTANT AND NON-BIRD-RESISTANT SORGHUM GRAIN ON AMINO-ACID DIGESTION BY BEEF HEIFERS

The effects of sorghum type on acid digestion were determined by feedi ng heifers (230 kg) equipped with ruminal, duodenal, and ileal cannula s bird-resistant (BR) or non-BR grains that had a normal or waxy endos perm (NORMAL-BR, WAXY-BR, NORMAL, WAXY). Dry-rolled grain diets were f ed 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 acid s of microbial protein from total flow. Flow (grams/day) of total and feed TAA, EAA, NAA, and proline-rich-protein (sum of aspartate, glutam ate, glycine, and proline) to the duodenum was greater (P < .05) for B R than for non-BR grains. The ratio between feed proline-rich-protein and NAA reaching the duodenum was similar to that noted with feed inta ke. Amino acid disappearance (grams/day) from the small intestine was unchanged (P > . 1 0) by sorghum type, although the digestibility (per centage of duodenal flow) of TAA, EAA, NAA, and most individual amino acids was decreased (P < .05) for BR varieties. Amino acid flow to the cecum (grams/day) was generally greater for NORMAL-BR than for WAXY-B R (P < .10) or for NORMAL (P < .01) and greater (P < .10) for WAXY-BR than for WAXY. Condensed tannins in BR sorghum grain seem to decrease small intestinal amino acid digestibility by increasing indigestible f eed protein flow to the duodenum, rather than by increasing the supply of endogenous protein or inhibiting digestive enzymes.