New methodology for estimating rumen protein degradation using the in vitro gas production technique

This paper explores the possibility of estimating in vitro degradable crude protein (IVDP) and effective crude protein (CP) degradation (EPD) of protein feeds in the rumen using a new method based on the in vitro gas production (GP) technique of Raab et al. [Raab, L., Cafantaris, B., Jilg, T., Menke, K.H., 1983. Rumen protein degradation and biosynthesis. 1. A new method for determination of protein degradation in rumen fluid in vitro. Br. J. Nutr. 50, 569–582]. Cold-pressed hempseed cake, cold-pressed rapeseed cake, rapeseed expeller, heat-treated rapeseed meal and soybean meal, used as test feeds, were incubated with buffered rumen fluid and carbohydrates at four concentrations, and amounts of ammonia-N and gas produced were measured after 4, 8, 12, 16, 24, and 30 h. The new GP technique included a number of methodological changes. Samples for ammonia-N analysis were collected from the same flask at every sampling time, and rumen fluid was pre-incubated with carbohydrates to enhance microbial activity and reduce background ammonia-N levels. Results using the new methodology showed that feed, time and feed × time interaction all affected IVDP estimates (P<0.01). Estimated EPD values obtained using the GP method were affected by feed (P<0.001), and were 0.33, 0.36, 0.46, 0.59 and 0.67 for hempseed cake, rapeseed meal, rapeseed expeller, rapeseed cake and soybean meal, respectively. We conclude that the new GP technique, compared to the original method, can provide more practical estimates of IVDP that enable calculations of EPD values of protein feeds. Additional studies are required to further validate the reliability of the method using feeds with known in vivo responses in order to develop the technique into a useful method for estimating CP degradation in the rumen.