USE OF N-15-AMINO ACID ISOTOPE-DILUTION TECHNIQUES TO DETERMINE ENDOGENOUS AMINO-ACIDS IN ILEAL DIGESTA IN GROWING PIGS

An experiment was carried out to determine the contribution of endogen ous amino acids (AA) to total AA, using the N-15-AA and N-15-leucine i sotope dilution techniques, in ileal digesta from growing pigs. Four b arrows, initial body weight (BW) 33.8 +/- 1.0 kg, were fitted with a s imple T-cannula at the distal ileum and one catheter in each of the ex ternal jugular veins. The pigs were fed 1.65 kg day(-1) of a wheat, fi sh meal and casein-based diet, formulated to contain 180 g protein (N x 6.25) day kg(-1). N-15-leucine, dissolved in saline, was infused int o 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 ra nged from 17.0 to 84.5%, to total AA in ileal digesta was determined f rom the dilution of N-15-enrichment (atom percent excess) in the indiv idual AA in digesta compared with free AA in blood plasma. In addition , the dilution of N-15-enrichment in leucine in digesta compared with free leucine in blood plasma was used to predict the endogenous contri bution 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 inta ke (DMI)(-1). Endogenous AA outputs ranged from 0.13 to 2.79 g kg DMI- 1 and real ileal digestibilities, calculated by correcting apparent di gestibilities for endogenous losses, ranged from 73.2 to 97.6%. In con clusion, N-15-amino acid isotope dilution techniques may estimate accu rately the endogenous contribution of protein and AA to total protein and AA in ileal digesta.