Effect of forage species, ryegrass water soluble carbohydrate concentration, and red clover polyphenol oxidase activity on in vitro rumen efficiency of nitrogen utilization

A relatively small proportion of the nitrogen (N) consumed by the ruminant is transferred into meat (5-15%) or milk (15-30%), and most of the rest is excreted, with potential impacts on water, soil and air quality. Many fresh forage diets used for dairy cows present an imbalance between the rapidly available N and the slowly available energy in the rumen, which can limit microbial protein synthesis and increase excretion losses. In this experiment two strategies to improve the dietary energy/protein balance and their effects on microbial synthesis were studied. The first was to use perennial ryegrass (Lolium perenne) bred to express high water soluble carbohydrate (HWSC) concentrations. The second was to reduce and/or delay protein degradation in the rumen, to improve the energy/N synchronisation, by employing the activity of the enzyme polyphenol oxidase (PPO) in red clover (Trifolium pratense; RC). The latter promotes the formation of protease resistant cross-linked protein complexes (Lee et al., 2004).