Digestibility of amino acids in barley, wheat, oats, and wheat middlings in growing swine measured at the end of the small intestine and over the total digestive tract

Abstract

Barley (TAMBAR 401), wheat (TAM 101), oats (Coker 234), and wheat middlings were fed to 40 kg cannulated pigs to determine amino acid (AA) digestibilities at the end of the small intestine and over the total tract. Percentages of protein and lysine among the four feedstuffs varied widely (14.3, .44; 14.5, .38; 11.6, .43; 15.73, .66; for barley, wheat, oats, and wheat middlings, respectively). Grains were ground twice with a hammer mill (4mm screen) before mixing. Casein (3%) was added to each grain diet, but not to wheat middlings. A replicated 3 x 3 Latin square design was used for the barley, wheat, and wheat middlings diets. The oat diet was fed to four pigs in a fourth period. Pigs were maintained in stainless steel metabolism cages and fed equally. Apparent digestibility of AA measured at the terminal ileum and over the total tract tended to be highest in the wheat diet, lowest for wheat middlings with barley and oats intermediate. Measured in ileal digesta, average digestibility of essential amino acids (EAA) was 85.97, 84.90, 84.31, and 81.18% for wheat, oats, barley, and middlings, respectively. Among the EAA, threonine and tryptophan were either first or second lowest in all but wheat middlings. Arginine, histidine, methionine, and phenylalaline digestibilities were consistently high in all four feedstuffs. Similar lysine digestibilities for all diets (82.58 to 84.46%) suggests that differences in digestibilities of the other AA have little practical importance. Digestibilities determined over the total tract were generally higher than those measured at the end of the small intestine but the same relative differences were found. Average digestibility for EAA was: wheat (91.43%), oats (89.47%), barley (87.08%), and middlings (79.09%). Among the EAA, lysine and threonine digestibilities were lowest or second lowest in all four feedstuffs. Differences in nitrogen digestibility between the sampling sites were fairly uniform among the four feedstuffs (5.1 to 6.4%) but there was a wide difference in individual AA and among feedstuffs. Unexpectedly, middlings showed a net increase in 10 AA in the large intestine resulting in an increase in digestibility of 2.09% for the EAA. Synthesis in the hind gut has been reported by others but the number of amino acids and the amount of synthesis found here is unusual...