Effect of essential: Total N ratio on endogenous amino acid losses and N retention in growing pigs

The effect of dietary essential:total (E/T) N ratio on endogenous amino acid losses (EAAL), endogenous losses of total N (ENL) and N retention (NR) was studied in ileally cannulated pigs. The treatments were a protein-free (PF) diet and four isonitrogenous (1.2% N) purified diets with E/T ratios of 0, 0.33, 0.66 and 1.0 (diets ET0, ET33, ET66 and ET100). The highest ENL (g per kg dry matter intake) were found in diet ET0 (2.56) followed by diets PF, ET33, ET66 and ET100 (2.24, 1.43, 1.33 and 1.25, respectively). A similar response was found for EAAL. In most cases, EAAL in pigs fed diets ET33, ET66 and ET100 were significantly lower than those in pigs fed diet ET0. The high ENL in diets PF and ET0 were largely due to the high endogenous losses of proline and glycine, the sum of which accounted for 36–42% of total EAAL. The proportion of diaminopimelic acid of total AA in ileal digesta was low, suggesting that the contribution of intestinal microflora to EAAL was negligible. N retention increased curvilinearly as the E/T ratio increased and reached the maximum at E/T value of 0.74.