Effect of starch infusion at the terminal ileum on nitrogen balance and apparent digestibilities of nitrogen and amino acids in pigs fed meat-and-bone and soybean meal diets.

Growing pigs were each surgically fitted with a single T-shaped cannula at the terminal ileum, and fed a cornstarch-based diet made isonitrogenous with meat-and-bone meal (MBM) or soybean meal (SBM). Starch or water was infused through the cannulas and the effects on N balance and apparent digestibilities (AD) of N and amino acids (AA) were studied. The infusion of starch, as contrasted to water, increased (P less than .01) excretion of fecal N and decreased (P less than .05) excretion of total urinary N, including urinary urea N, without affecting the amount of N retained. The increased excretion of fecal AA following starch infusion resulted in lowered (P less than .05) AD (percentage units) of indispensable AA, threonine (8.4), methionine (6.7), valine (6.6) and lysine (5.0); and dispensable AA, tyrosine (6.9) and aspartic acid (5.7). The same pattern of AD decreases was obtained for both protein sources, but in general, the magnitude of these decreases was greater for MBM than for SBM. Large differences (percentage units) were observed between AD of individual AA and that of N (arginine, +11.2 and isoleucine, -5.2, in MBM; arginine, +7.6 and methionine, -7.6, in SBM). Results showed that the route of N excretion and the AD of N and AA, as determined by the fecal analysis method, were influenced by the amount of starch entering the hindgut. It was concluded that AD of individual AA, and not N, should be considered when formulating pig diets; however, because of the dependence of AD values on starch entering the hindgut, AD values (fecal analysis method) may not be reliable measures of AA availabilities.