METHODS OF MANIPULATING THE MICROBIAL-METABOLISM IN THE RUMEN

We now have the means to increase or decrease the importance of the ro le of the rumen in ruminant digestion. The aim of these manipulations is to provide the animal with end products of digestion that are the b est suited to the type of production required. We describe here the ma in additives and methods used to modify the rumen microbial population or its hydrolytic and fermentative activities: ionophore antibiotics; methane inhibitors; inhibitors of proteolysis or deamination; elimina tion of protozoa or fungi from the rumen; and probiotics. Some seem to have a well-defined action (inhibitors of methanogenesis and deaminat ion), whereas others act on several targets (ionophore antibiotics, de faunation). The results observed in animal production depend on factor s such as diet, type of production and the animal considered. The rume n should be considered as a balanced integrated system in which it is difficult to change only one variable. For example, the increase in th e NADH/NAD ratio is related to the decrease in methanogenesis in the r umen but has repercussions on other factors concerning digestion, lead ing to a decrease in cellulolysis, deamination of amino acids and an i ncrease in propionate or butyrate at the expense of acetate. The mode of action of some additives is not yet fully understood and the effica cy of probiotics has sometimes been openly contested. Studies presentl y in progress should make it possible to classify the different compou nds on the market according to their effectiveness and to establish th e conditions under which they should be used. Once the mechanisms of a ction are elucidated, research into new products will be more closely targeted. Genetic manipulation is an interesting approach to the contr ol of the metabolism of rumen microbes but has so far yielded no concr ete results.