Prediction of available energy and amino acid digestibility of Chinese sorghum fed to growing-finishing pigs

Two experiments were conducted to determine digestible energy (DE), metabolizable energy (ME), as well as the standardized ileal digestibility (SID) of crude protein (CP) and amino acids (AA) in 10 sorghum samples fed to pigs. In experiment 1, 22 crossbred barrows (Duroc x Yorkshire x Landrace, Initial body weight [BW]: 70.0 +/- 1.8 kg) were selected and allotted to a replicated 11 x 3 incomplete Latin square design, including a basal diet and 10 sorghum energy diets and three consecutive periods. Each period had 7 d adaptation and 5 d total feces and urine collection. The DE and ME were determined by the total collection and the difference method. In experiment 2, 22 crossbred barrows (Duroc x Yorkshire x Landrace, Initial BW: 41.3 +/- 1.2 kg) that had a T-cannula installed in the distal ileum were assigned to a replicated 11 x 3 incomplete Latin square design, including an N-free diet and 10 sorghum diets. Each period had 5 d adaptation and 2 d ileal digesta collection. The basal endogenous N losses were measured by the N-free diet method. All diets in experiment 2 were added 0.30% titanium dioxide as an indigestible marker for calculating the ileal CP and AA digestibility. On an as-fed basis, the DE and ME contents in sorghum were 3,410 kcal/kg (2,826 to 3,794 kcal/kg) and 3,379 kcal/kg (2,785 to 3,709 kcal/kg), respectively. The best-fit prediction equation for DE and ME were DE = 6,267.945 - (1,271.154 x % tannin) - (1,109.720 x % ash) (R2 = 0.803) and ME = 51.263 + (0.976 x DE) (R2 = 0.994), respectively. The SID of CP, Lys, Met, Thr, and Trp (SIDCP, SIDLys, SIDMet, SIDThr, and SIDTrp) in 10 sorghum samples were 78.48% (69.56% to 84.23%), 74.27% (61.11% to 90.60%), 92.07% (85.16% to 95.40%), 75.46% (66.39% to 80.80%) and 87.99% (84.21% to 92.37%), respectively. The best prediction equations for SID of CP and the first four limiting AAs were as following: SIDCP = 93.404 - (21.026 x % tannin) (R2 = 0.593), SIDCP = 42.922 - (4.011 x % EE) + (151.774 x % Met) (R2 = 0.696), SIDLys = 129.947 - (670.760 x % Trp) (R2 = 0.821), SIDMet = 111.347 - (232.298 x % Trp) (R2 = 0.647), SIDThr = 55.187 + (3.851 x % ADF) (R2 = 0.609) and SIDTrp = 95.676 - (10.824 x % tannin) (R2 = 0.523), respectively. Overall, tannin and ash are the first and second predictors of DE and ME values of sorghum, respectively, and the tannin, EE, Trp, ash, CF, and ADF can be used as the key predictors for SID of CP and first four limiting AAs. The manuscript provided the prediction equations for digestible energy, metabolizable energy, and standardized ileal amino acid digestibility in 10 sorghum samples fed to growing-finishing pigs based on available chemical components, which enrich the ingredient database and provide help for feed enterprises to make full use of Chinese sorghum. In this manuscript, we selected and analyzed the chemical composition of 10 different varieties of Chinese sorghum. Two digestion and metabolism experiments were conducted to measure the concentrations of available energy (digestible energy and metabolizable energy) and ileal amino acid digestibility (apparent or standardized ileal amino acid digestibility) in sorghums fed to pigs. The results showed as following: 1) The available energy values of 10 sorghum samples varied greatly, and the ileal digestibility of some amino acids also differed. 2) The available energy value and the ileal digestibility of crude protein and amino acids can be predicted by the contents of chemical components in sorghum, such as tannin (a substance in sorghum that can bind to biological macromolecules like proteins), ash, tryptophan, and fiber composition, etc. The above findings enrich the ingredient database and assist for feed enterprises to make precise formulations when using the Chinese sorghum.