Background and methodology
Earlier studies with legume silages identified increased intake and milk production in comparison with grass silages. Red clover silage led to increased levels of α-linoleic acid in milk, whilst there was increased N-use efficiency with white clover. Some studies have demonstrated higher rates of passage from the rumen for fresh alfalfa in comparison with fresh grass. Other studies showed an increased rate of particle breakdown in the rumen of sheep offered dried perennial rye-grass. The objective of this study was to understand the rumen mechanisms that lead to the differences between ryegrass silage and legume silages in feed intake.
Legume silages led to increased dry matter intake and milk production in comparison with grass silage. The inclusion of white clover or alfalfa silage, but not red clover silage in diets led to an increase in molar proportions of iso-butyric, iso-valeric and n-valeric acids in comparison with diets based on grass silage. Microbial energetic efficiency was highest for cows offered alfalfa silage, intermediate for clover silage and lowest for cows fed grass silage. Although the biohydrogenation of α-linoleic acid was still high for red clover silage (86.1% compared with 94.3% for grass silage), there was a 240% increase in the proportion of α-linoleic acid passing through the rumen.
Dewhurst, R. J., Evans, R. T., Scollan, N. D., Moorby, J. M., Merry, R. J. & Wilkins, R. J. (2003). Comparison of grass and legume silages for milk production. 2. In vivo and in sacco evaluations of rumen function. J. Dairy Sci. 86:2612-2621.