Use of 15N‐amino acid isotope dilution techniques to determine endogenous amino acids in ileal digesta in growing pigs

Abstract

An experiment was carried out to determine the contribution of endogenous amino acids (AA) to total AA, using the 15N‐AA and 15N‐leucine isotope dilution techniques, in ileal digesta from growing pigs. Four barrows, initial body weight (BW) 33.8 ± 1.0 kg, were fitted with a simple T‐cannula at the distal ileum and one catheter in each of the external jugular veins. The pigs were fed 1.65 kg day−1 of a wheat, fish meal and casein‐based diet, formulated to contain 180 g protein (N x 6.25) day kg−1. 15N‐leucine, dissolved in saline, was infused into the right catheter at a rate of approximately 40 mg kg BW−1 day−1 for a total of 9 days. The contribution (%) of endogenous AA, which ranged from 17.0 to 84.5%, to total AA in ileal digesta was determined from the dilution of 15N‐enrichment (atom percent excess) in the individual AA in digesta compared with free AA in blood plasma. In addition, the dilution of 15N‐enrichment in leucine in digesta compared with free leucine in blood plasma was used to predict the endogenous contribution of the other AA, which ranged from 13.9 to 36.0%, and protein (17.4%). The endogenous output of protein was 7.59 g kg dry matter intake (DMI)−1. Endogenous AA outputs ranged from 0.13 to 2.79 g kg DMI−1 and real ileal digestibilities, calculated by correcting apparent digestibilities for endogenous losses, ranged from 73.2 to 97.6%. In conclusion, 15N‐amino acid isotope dilution techniques may estimate accurately the endogenous contribution of protein and AA to total protein and AA in ileal digesta.