Rumen-undegradable protein of blood meal, canola meal, low-fat distillers dried grain with solubles, soybean meal, and expeller soybean meal determined using in situ and in vitro ammonia release procedures
Two Holstein cows (days in milk 70 ± 17 and milk yield 27.3 ± 8.00 kg) fitted with ruminal cannulas were used to determine rumen-undegradable protein (RUP) using an in situ incubation of 16. In addition, the in vitro ammonia (NH3) release procedure was used to estimate RUP. The in vitro NH3 release procedure involves the incubation of equal amounts of N from each feedstuff in ruminal fluid and the measurement of the NH3 and total VFAs produced. Concentrations of NH3and total VFA were adjusted for a blank (only inoculum). The feedstuffs evaluated were: 3 sources of blood meal (BM1, BM2, and BM3), canola meal (CM), low-fat distillers dried grains with solubles (LFDG), soybean meal (SBM), and expeller soybean meal (ESBM). Data from the in situ procedure were analyzed as a randomized complete block design and the model included the fixed effect of feedstuff and the random effects of replicate and load within feedstuff and data from the in vitro ammonia release were analyzed as a complete randomized design and the model included the fixed effect of feedstuff and the random effect of load within feedstuff. Based on the in situ procedure, RUP was 70.2, 63.0. 59.3, 31.2, 24.3, 23.1, 14.7 ± 3.93% crude protein (CP) for BM2, ESBM, BM3, SBM, CM, LFDG, and BM1, respectively. Based on the in vitro ammonia release procedure, RUP was 67.6, 67.5, 65.8, 48.8, 32.5, 32.3, 32.1 ± 3.46% CP for BM2, BM3, ESBM, LFDG, BM1, SBM, and CM. Compared to RUP values obtained from the in situ procedure, values of RUP from the in vitro ammonia release procedure were greater (P = 0.01) for BM1 and LFDG and similar (P ≥ 0.10) for the remaining feedstuffs. The in vitro ammonia release procedure is a promising method for measuring RUP that avoids the use of cannulated animals and errors that may emerge with washout of residue from the polyester bags, and allows for uniform settings; however, more research is needed to elucidate the factors that cause variability when using this procedure.
Keywords: rumen-undegrabable protein, in situ, in vitro