Ileal endogenous amino acid flow response to nitrogen-free diets with differing ratios of corn starch to dextrose in broiler chickens

An experiment was conducted to determine response in digestibility of DM and the AA composition of ileal endogenous flow of 26-d-old broilers to nitrogen-free diets (NFD) formulated with different ratios of corn starch to dextrose. A total of four hundred eighty 3-wk-old broiler chickens were used in a 4-d trial to estimate ileal endogenous flow (IEF) of amino acid (AA). The ratios of dextrose to corn starch investigated were 0:849, 283:566, 566:283, or 849:0 for diet numbers 1, 2, 3, or 4, respectively. All diets contained a calculated dietary electrolyte balance of 115 mEq/kg and chromic oxide (5 g/kg) as an indigestible marker. The birds received a standard starter diet from d 1 to 22 posthatch. On d 22 posthatch, all the birds were weighed and allocated to 4 treatments in a randomized complete block design. On d 26 posthatch, birds were asphyxiated with CO₂ and ileal digesta was collected. Ileal DM digestibility was lowest in diet 1 (77.9%) and increased as the proportion of corn starch in the diet decreased. The IEF for all the indispensable AA were different (P < 0.01) among diets with the exception of Thr, which was not (P = 0.07). The respective IEF of AA (mg/kg of DMI) in birds fed diets 1, 2, 3, or 4 were 630, 664, 646, or 1,235 for Lys, 173, 172, 177, or 361 for Met, and 68, 74, 70, or 166 for Trp. For the dispensable AA and total AA, IEF of most AA except for Cys and Pro was highest (P < 0.01) in diet 4. Ileal endogenous flow of Pro was not different among diets. Diet 4 had the lowest (P < 0.01) IEF of Cys, whereas there was no difference among other diets. In conclusion, the data from the current study show that the variation in proportion of corn starch and dextrose in a nitrogen-free diet may affect estimates of ileal endogenous flows of N and AA.