Fiber matrix of assay feedstuffs modulates the effect of fat type on standardized ileal amino acid digestibility in broiler chickens.

Experiment 1 investigated the interactivity of fiber feedstuff and fat type on standardized ileal amino acid digestibility (SIAAD), the morphology of the digestive organs, cecal content pH, and short-chain fatty acid (SCFA). Experiment 2 examined how the dietary inclusion level of lard influences the SIAAD of soybean meal (SBM). For Expt. 1, 260 broiler chicks were allocated to 52 metabolism cages (six diets with six replicates), plus two nitrogen-free diets (NFD). In Expt. 2, 160 broiler chickens were allocated to 32 metabolism cages (four diets with eight replicates). All birds received a basal corn-SBM diet from d 0 to 16, followed by experimental diets from d 16 to 21. In Expt. 1, the diets were semi-purified diets with corn, wheat, or wheat bran as the sole source of dietary protein, each with either soybean oil or lard as the dietary fat (3 × 2 factorial). In Expt. 2, the diets containing SBM as the sole protein source were formulated with four dietary levels of lard (10-40 g/kg). On d 21, ileal digesta (Expt. 1 and 2), and small intestine sections, gizzard, pancreas, and cecal content (Expt. 1 only) were collected. In Expt. 1, there was a significant feedstuff × fat type (P < 0.05) for SIAAD of most AA. The SIAAD of corn was unaffected, whereas wheat and wheat bran had higher SIAAD values with lard and soybean oil, respectively. Birds fed the wheat bran diets had greater (P < 0.05) relative weights of the small intestine and the gizzard. In Expt. 2, a quadratic increase in SIAAD of all AA as the lard level increased was observed (P < 0.01). In conclusion, the the SIAAD effect of assay diets containing different fat type was dependent on the fiber matrix of the assay feedstuff and the quadratic SIAAD response to inclusion level of lard indicates a dose-dependent effect of lard inclusion on AA digestibility.