Assessment of the interactive effect of dietary fat and feedstuff types on basal endogenous amino acid flow, coefficients of standardised ileal amino acid digestibility, the morphology of small intestine and jejunal mucosa gene expression in broiler

1. The objective of Experiment 1 was to determine the effect of fat source on basal endogenous losses of amino acids (BEL), histomorphology of the small intestine and caecal short-chain fatty acid (SCFA). Experiment 2 was conducted to determine the interactive effect of feedstuffs and fat types on coefficients of standardised ileal amino acid digestibility (cSIAAD) of maize and soybean meal (SBM), histomorphology of jejunum and ileum and the relative gene expression of amino acid transporters in the jejunal mucosa.2. In Experiment 1, a total of 80 broiler chickens were allocated to 16 metabolic cages (two diets, eight replicates each). Two nitrogen-free diets were formulated with soybean oil (25 g/kg, NFDS) or tallow (35 g/kg, NFDT) as fat sources. A total of 160 broiler chickens were allocated to 32 metabolic cages (four diets, eight replicates each) in Experiment 2. Four semi-purified diets consisted of maize or SBM as the sole protein source, each supplemented with either soybean oil or tallow as the fat type.3. In Experiment 1, there was no significant effect for any of the responses. In Experiment 2, there were no feedstuff × fat type interactions for any of the responses. The cSIAAD for Leu, Ala, Cys and Glu were greater (<i>p</i> < 0.05) for maize. The jejunal and ileal villi were longer, ileal crypts deeper and the relative expressions of peptide and amino acid transporter genes were greater (<i>p</i> < 0.05) for birds that received the SBM diets.4. In conclusion, under the conditions of this experiment, cSIAAD values determined with assay diets using the two fat types were similar.