Ruminal Degradation of Rubisco by Beef Cattle Grazing Switchgrass and Big Bluestem

This two-year study was conducted on monocultures of switchgrass and big bluestem to: (1) determine the concentration of the protein ribulose-1,5- bisphosphate carboxylase (Rubisco), found only in the bundle sheath cells of warm-season grasses, in omasal, masticate and fecal samples of grazing cattle; and (2) estimate rumen-escape Rubisco via bundle sheath cells. A quantifying enzyme-linked immunosorbent assay, along with estimates of rumen and lower tract digestibilities, indicated as much as 11% of Rubisco in big bluestem and 13% in switchgrass escaped rumen degradation and was absorbed in the lower tract. Realizing these amounts of escape Rubisco represent a significant level of soluble protein, bundle sheath cells may provide a mechanism allowing soluble protein to escape ruminal degradation