Rumen Protein Degradation Characteristics Among Six Protein Feed Sources Using a Batch Culture System.

Soybean meal (SBM), dried distiller’s grain with solubles (DDGS), porcine blood meal (BM), cottonseed meal (CSM), and fish meal (FM) were used to measure nitrogen degradation rate (Kd) in a batch culture system by different mathematical models. We hypothesized protein Kd would differ among feeds when expressed as absolute rate (%/h) and would not differ among feeds when expressed as fractional rate (%/h on potentially digestible). Four experiments were conducted to estimate protein Kd (48h incubation). Two degradation curves were generated for each feed and SBM was used as a control for all four experiments. Ammonia release was used as an indicator of nitrogen degradation, which was measured at 0, 2, 4, 8, 16, 24 and 48h post flask inoculation. Data were analyzed as a completely randomized design with flask as experimental unit using the GLM procedure of SAS (Version 9.3, Cary, NC). Absolute and fractional degradation rate were determined from linear and quadratic regressions. Coefficient of determination was greater for quadratic than linear regression equations for SBM (quadratic R² = 0.96, linear R² = 0.88; P = 0.005) and FM (quadratic R² = 0.95, linear R² = 0.85; P = 0.007), however CSM, DDGS and BM did not differ (P > 0.05). Fractional degradation rate, estimated using quadratic regression did not differ among feed sources (P = 0.08). Linear regression equations estimated similar protein degradation among feed sources except for DDGS which had a faster degradation rate than other feed sources. In conclusion, using quadratic regression equations to estimate protein degradation better agrees with measured protein degradation data than thus linear regression equations.