FACTORS AFFECTING DEGRADATION OF BARLEY STRAW IN-SACCO AND MICROBIAL ACTIVITY IN THE RUMEN OF COWS FED FIBER-RICH DIETS II - THE LEVEL OF SUPPLEMENTAL FISH-MEAL

A diet composed of 76.2% untreated barley straw + 23.8% rye grass hay was given to three nonlactating cows at 90% of ad libitum intake. The cows were supplemented via cannulae with three different levels of fis hmeal in order to make the ration up to 8%, 10% and 14% crude protein on a dry-matter basis. Treatments were arranged in a Latin Square desi gn. Nylon bags containing untreated barley straw were incubated in the rumen of the cows for up to 72 h. Degradability of dry matter, total organic matter and the individual components of the cell wall of barle y straw were affected by the protein level of the diet. The inclusion of fishmeal to a level of 14% dietary protein produced the highest deg radability of all parameters measured. The protein level also affected ammonia and total VFA concentrations; both fermentation products were highest in the treatment with the high fishmeal level, Rumen pH and r umen outflow rate of liquid and particulate phases were not affected b y protein level, The ATP concentration found in the solid residue, rem aining after removal of the liquid phase from the rumen content, incre ased with increasing fishmeal level, while ATP in the liquid phase rem ained unchanged. This indicates that, under the conditions of this stu dy, fishmeal exerts its effects on the microbes intimately associated to the fibre, and not upon the whole microbial population. The microbi al DNA concentration of digesta within nylon bags increased during the first 24 h of incubation and then decreased until the end of incubati on, indicating a process of colonization and depletion of degradable s ubstrates. (C) 1998 Elsevier Science B.V.