Factors affecting degradation of barley straw in sacco and microbial activity in the rumen of cows fed fibre-rich diets. I. The source of supplemental nitrogen

Abstract

Untreated barley straw was incubated in nylon bags for up to 72 h in the rumen of three non-lactating dairy cows fed restricted amounts of a diet composed of 76% untreated barley straw and 24% grass hay, and supplemented with urea, casein, soybean meal or fishmeal to make the ration up to 12% protein. The experiment followed an incomplete balanced block design. Fishmeal produced the highest degradability of dry matter, organic matter, cellulose, hemicellulose and individual sugars. For most components of the barley straw, urea produced the lowest results. The source of nitrogen also affected rumen pH, ammonia and volatile fatty acid concentrations, but had no effect upon rumen outflow rate of liquid or particulate phases. Microbial activity was higher in fishmeal and soybean meal than in urea and casein and highest in fishmeal in the residue after extraction of most of the rumen liquid, suggesting that fishmeal exerts its effect upon microbes intimately associated with the fibre and not upon the whole bacterial population. Microbial activity and biomass within the nylon bags were never constant but related to processes of colonization and depletion of degradable substrate.