Concentrations of analyzed or reactive lysine, but not crude protein, may predict the concentration of digestible lysine in distillers dried grains with solubles fed to pigs

The objectives of this experiment were to evaluate procedures that may be used to predict the concentration of standardized ileal digestible (SID) Lys in distillers dried grains with solubles (DDGS) fed to pigs and to evaluate the accuracy of a published equation to predict SID Lys in DDGS. Twenty-one sources of DDGS were analyzed (as-fed basis) for CP (23.8% to 33.6%; CV = 8.3%), Lys (0.69% to 1.17%; CV = 12.4%), and furosine (0.02% to 0.22%; CV = 91.4%). The concentration of reactive Lys (%, as-fed basis) was calculated as analyzed Lys (%) - furosine (%) divided by 0.32 x 0.40 and ranged from 0.47% to 1.15% (CV = 20.7%) in the 21 sources of DDGS. Twenty-one diets that each contained 60.0% of 1 source of DDGS as the sole source of CP and AA were formulated. An N-free diet was also formulated and was used to determine basal endogenous losses of CP and AA. Twenty-two barrows with an initial BW of 45.2 kg (SD = 3.1 kg) were fitted with a T-cannula in the distal ileum and allotted to a 22 x 10 Youden square design with the 22 diets and 10 periods. The SID of CP and AA were calculated for each source of DDGS. The SID of CP ranged from 69.8% to 79.6%, and the SID of Lys ranged from 45.3% to 74.1%. The concentration of SID Lys in the 21 samples of DDGS was highly related to the concentration of analyzed Lys (P < 0.001; r(2) = 0.849) and with the concentration of reactive Lys in the samples (P < 0.001; r(2) = 0.898). In contrast, the concentration of SID Lys in the 21 sources of DDGS was not related to the concentration of CP in the samples (P = 0.558; r(2) = 0.021). However, values for SID Lys were in good agreement with values predicted using a published prediction equation. In conclusion, analyzed Lys in DDGS, but not CP, may be used to predict the concentration of SID Lys in DDGS fed to pigs. However, analysis of furosine in addition to Lys and subsequent calculation of reactive Lys improve the prediction accuracy of digestible Lys concentration in DDGS.