Determination and prediction of amino acid digestibility in brown rice for growing-finishing pigs.

Objective The experiment aimed to determine the standardized ileal digestibility (SID) of crude protein (CP) and amino acids (AA) in 10 brown rice samples fed to pigs, and to construct predictive models for SID of CP and AA based on the physical characteristics and chemical composition of brown rice. Methods Twenty-two cannulated pigs (initial body weight: 42.0±1.2 kg) were assigned to a replicated 11×3 incomplete Latin square design, including an N-free diet and 10 brown rice diets. Each period included 5 d adaptation and 2 d ileal digesta collection. Chromic oxide was added at 0.3% to all the diets as an indigestible marker for calculating the ileal CP and AA digestibility. Results The coefficients of variation of all detected indices for physical characteristics and chemical composition, except for bulk weight, dry matter (DM) and gross energy (GE), in 10 brown rice samples were greater than 10%. The SID of CP, lysine (Lys), methionine (Met), threonine (Thr) and tryptophan (Trp) in brown rice was 77.2% (62.6% to 85.5%), 87.5% (80.3% to 94.3%), 89.2% (78.9% to 98.9%), 55.4% (46.1% to 67.6%) and 92.5% (86.3% to 96.3%), respectively. The best prediction equations for the SID of CP, Lys, Thr and Trp were as following, SIDCP=﹣664.181+8.484×DM (R2=0.40), SIDLys=53.126+6.031×ether extract (EE) +0.893×thousand-kernel volume (R2=0.66), SIDThr=39.916+7.843×EE (R2=0.41) and SIDTrp=﹣361.588+4.891×DM+0.387×total starch (R2=0.85). Conclusion Overall, a great variation exists among 10 sources of brown rice, and the thousand-grain volume, DM, EE, and total starch can be used as the key predictors for SID of CP and AA.