Similarity of rumen degradable protein (RDP) degradation rates comparing in vitro and in situ techniques


Brooks M, Johnson N, Harvey R, Kerley M. 2009. Similarity of rumen degradable protein (RDP) degradation rates comparing in vitro and in situ techniques. In Ward A, Treiber K, Schmidt D, Coslik A, Maslanka M, Eds. Proceedings of the Eighth Conference on Zoo and Wildlife Nutrition, AZA Nutrition Advisory Group, Tulsa, OK.


Protein provided to ruminants can be divided into rumen degradable protein (RDP) and rumen undegradable protein (RUP). The RDP provides amino acids and ammonia-nitrogen which are vital to the growth of rumen microbes. An imbalance of the RDP supply and microbial RDP requirement can alter ruminal fermentation. The imbalance could lead to reproductive inefficiencies, inadequate growth, and ruminal acidosis. To better estimate RDP provided to the rumen, it is necessary to know the rate at which the RDP degrades. One in situ and two in vitro experiments were performed measuring degradation rates of varying protein sources (bloodmeal, BM; dried distillers grain, DDG; dried distillers grain with solubles, DDGS; casein, C; soybean meal, SBM; corn gluten feed, CGF; and a RUP mix) using dairy cow rumen fluid. The in situ method measured remaining nitrogen over a time course of 0 to 72 h, while the in vitro methods measured ammonia release as a measure of nitrogen degradation over a time course of 0 to 48 h. The data were analyzed to determine the proportion of RDP degraded over time when taken to complete degradation (extent). The plotted proportions of degraded RDP over time result in a linear decline with slope a measure of degradation rate (Kd). The Kd ranged from 1.91-2.84% h-1. Bloodmeal had the lowest rates at 2%, and the SBM had the rates at 2.8%; however, BM, DDG, DDGS, C and the RUP mix were similar (P>0.01). There was no difference between in situ and in vitro methods (P=0.26). These similar rates will help improve estimation of protein release in the rumen, thus helping accurately balance RDP with microbial requirements.

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