Digestibilities of amino acids, nitrogen, energy and starch in corn, sorghum, wheat, barley, oat groats and wheat middlings in growing swine at the end of the small intestine and over the total digestive tract

Abstract

Nutrient digestibilities of yellow corn, low-tannin sorghum, hard red wheat, barley, oat groats and wheat middlings were determined at the end of the small intestine and over the total tract of growing pigs. All diets contained about 97% of the finely-ground test feedstuff and 3% mineral-vitamin supplementation. Thirty-six pigs cannulated at the terminal ileum, were used to give six observations for each product. Differences in apparent digestibilities of dry matter and gross energy at both locations and energy values for the diets reflected differences in fiber and fat content of the feedstuffs. Digestibilities of dry matter and gross energy for the low fiber feedstuffs (corn, sorghum, oat groats and wheat) were essentially equal, but digestibilities were lower for barley, and lowest for wheat middlings which contained the most fiber. Digestible and metabolizable energy values of the feedstuffs followed the same pattern, but were highest for oat groats due to its high fat content. Starch digestibilities were essentially 100% for all products when measured over the total tract. However, at the end of the small intestine values for barley and wheat middlings were slightly lower than the other products. At the end of the small intestine, amino acid digestibilities tended to be highest for wheat and oat groats, followed by corn and sorghum, then barley and wheat middlings. With the exception of lysine for sorghum and tryptophan for corn, differences in digestibility of the essential amino acids among all products (excluding wheat middlings) were small, ranging from 4 to 7 percentage units. Values for wheat middlings averaged about 10 percentage units lower than the remaining products. Among the essential amino acids, tryptophan was least digestible in corn (69%), lysine was least digestible in sorghum (73.8%) and threonine was least digestible in the remaining feedstuffs (63.5 to 77.9%). Amino acid digestibilities determined over the total tract were generally higher than small intestine digestibilities; however, some values were lower, indicating a synthesis of these amino acids in the large intestine. Because of the inconsistent effect of microbial action on amino acids in the large intestine, digestibilities determined at the end of the small intestine should more accurately estimate amino acid absorption.