Application of the Reactive Lysine Procedure To Estimate Lysine Digestibility in Distillers Dried Grains with Solubles Fed to Growing Pigs

Abstract

Two experiments were conducted to measure the reactive Lys concentration in corn distillers dried grains with solubles (DDGS). In expt 1, reactive Lys was measured in 33 sources of DDGS using two procedures: the homoarginine procedure and the furosine procedure. The concentration of reactive Lys in DDGS was then correlated with the concentration of standardized ileal digestible (SID) Lys in DDGS fed to growing pigs. In expt 2, a factorial experiment was conducted using four ratios of condensed distillers solubles (CDS) and wet distillers grain (WDG). The ratios (wt/wt) of CDS to WDG were 0:100, 20:80, 40:60, and 100:0, and four subsamples from each combination were freeze-dried or oven-dried at 50, 75, or 100 °C. The dried samples were designated DDG, DDGS₂₀, DDGS₄₀, and CDS, respectively. All subsamples were analyzed for total Lys and for reactive Lys using the homoarginine procedure. Results of expt 1 showed that only 74.1% of total Lys was reactive if measured by the homoarginine procedure and 83.5% was reactive if measured by the furosine procedure. The concentration of SID Lys in DDGS was correlated with the concentration of reactive Lys measured by the homoarginine procedure (r² = 0.70, P < 0.05) and by the furosine procedure (r² = 0.66, P < 0.05). In expt 2, the concentrations of total Lys and reactive Lys were reduced (P < 0.05) when addition of CDS or drying temperature of the samples was increased, but the reduction was greater (P < 0.05) when both CDS addition and drying temperature were increased at the same time. After oven-drying at 100 °C, 75.7% of total Lys was reactive in DDG, but only 27.6 and 10.2% were reactive in DDGS₂₀ and DDGS₄₀, respectively. In conclusion, reactive Lys is correlated with the concentration of SID Lys in DDGS, and addition of CDS exacerbates the negative effects of heating on the concentration of total Lys and reactive Lys in DDGS.