Prediction of available energy and amino acid digestibility in the Chinese paddy rice fed to growing pigs

Two experiments were conducted to determine digestible energy (DE), metabolizable energy (ME), and standardized ileal digestibility (SID) of crude protein (CP) and amino acids (AA) in Chinese paddy rice for growing pigs, and to establish prediction equations for DE, ME and SID of CP and AA based on its chemical composition including amylase-treated neutral detergent fiber (aNDF), acid detergent fiber (ADF), and calcium (Ca). In Exp. 1, twenty-four castrated barrows (20 ± 1.3 kg) were selected and allotted to a replicated 12 × 3 incomplete Latin square design, including 12 diets and 3 consecutive periods. A basal diet and 11 Chinese paddy rice diets were prepared and maintained a consistent ratio of corn to soybean meal. Each period had 7 d of adaptation and 5 d of fecal and urine collection. In Exp. 2, twenty-four ileal-cannulated pigs (15.4 ± 1.8 kg) were used in a duplicated 12 × 3 incomplete Latin square design with 12 diets and three consecutive periods, and each period had 5 d of adaptation and 2 d of ileal digesta collection. Chinese paddy rice was the sole nitrogen (N) source in 11 test diets, and an N-free diet was used for calculating the basal endogenous N losses. The results revealed that DE and ME values (as-fed basis) in Chinese paddy rice averaged 12.17 MJ/kg and 11.57 MJ/kg, respectively. The optimal prediction equations for DE and ME were DE (MJ/kg) = 20.12 − (0.56 × aNDF, %) + (130.01 × Ca, %) − (3.94 × phytic acid, %); R² = 0.94, RSD = 0.44, P < 0.001, and ME (MJ/kg) = −0.263 + (0.972 × DE, MJ/kg); R² = 0.96, RSD = 0.32, P < 0.001, respectively. The values for SID of CP (SID_CP), Lys (SID_Lys), Met (SID_Met), Thr (SID_Thr), and Trp (SID_Trp) in Chinese paddy rice were 0.735, 0.766, 0.687, 0.736, and 0.862, respectively. The best-fit equations for SID_CP, SID_Lys, and SID_Thr were SID_CP = 0.67 − (0.03 × ADF, %) + (0.06 × CP, %); R² = 0.79, RSD = 0.04, P = 0.002, SID_Lys = 1.18 + (4.34 × non-phytate phosphorus, %) − (6.71 × Trp, %) − (6.59 × Ca, %); R² = 0.93, RSD = 0.03, P < 0.001, and SID_Thr = 0.82 + (2.88 × Met, %) − (1.61 × Lys, %); R² = 0.83, RSD = 0.03, P = 0.001, respectively. In conclusion, our study revealed the relationships between the chemical composition of Chinese paddy rice and DE, ME, and the SID of the first four limiting AA for growing pigs, establishing the predicted models for the nutritive value of Chinese paddy rice fed to growing pigs. The aNDF, ADF, phytic acid, phytate phosphorus, non-phytate phosphorus, total phosphorus, CP, and Ca were the common key predictors for DE and ME. Dry matter, aNDF, and ADF were the common key predictors of SID_CP and SID_Lys. Crude fiber, ADF, and Met can be the single predictors of SID_Thr.