Ruminal availability of nitrogen and carbohydrates from fresh and preserved herbage in dairy cows.

Rumen degradabilities of crude protein and non-protein organic matter of fresh and preserved herbage, obtained with nylon bag studies, were compared and consequences for dairy cow rations discussed. Results from 4 experiments indicate that fresh and preserved herbage fertilized at high rates of nitrogen, had a large surplus of fermentable nitrogen. In fresh herbage the ratio of soluble nitrogen:soluble non-protein organic matter ("carbohydrates") was lower than the ratio of insoluble, degraded nitrogen:insoluble, degraded carbohydrates. It is concluded that ingredients with a low ratio of insoluble, degraded nitrogen:insoluble, degraded carbohydrates may be appropriate supplements for grass-based diets. In preserved herbage the ratio of soluble nitrogen:soluble carbohydrates exceeded the ratio of insoluble degraded nitrogen:insoluble degraded carbohydrates. Wilting had no consistent effect on the ratios of nitrogen:carbohydrates. Treatment with cell wall degrading enzymes gave a lower ratio of soluble nitrogen:soluble carbohydrates. It is suggested that silage-based diets require supplementation with ingredients high in soluble carbohydrates. (Abstract retrieved from CAB Abstracts by CABI’s permission)