Manipulation of fermentation and digestion to optimize the use of forage resources for ruminant production

Chemical manipulation of digestive fermentation in the ruminant is discussed in relation to: improving the utilization of the basal diet of grazing animals for meat, fibre and milk production; facilitating the use of starch based supplements; and reducing methane production. A range of ionophore compounds and other antibiotic rumen modifiers may significantly increase body weight in grazing animals. Some of these rumen modifiers have been found to increase wool and milk production under some dietary conditions. These compounds may be administered to grazing animals via mineral licks and blocks, drinking water, protein supplements or intraruminal slow release devices. A number of rumen modifiers, and virginiamycin in particular, may have a role in overcoming problems associated with feeding starch rich supplements such as cereal grains. These compounds control some of the negative effects which result from the rapid fermentation of starch and reduce the risk of lactic acid accumulation. Compounds such as virginiamycin allow grain supplements to be fed at weekly or fortnightly intervals and, in addition, the supplementary nutrients appear to be utilized more efficiently. A number of chemical agents are known which inhibit the production of methane gas during fermentation in the rumen. Reducing methane production in this way does not consistently improve the efficiency of feed conversion to the same extent as the ionophore compounds and for this reason the use of these agents has not been promoted commercially. In view of the rapid rise of atmospheric methane concentrations and the important role of this gas in the 'greenhouse effect' the potential for inhibiting methane production in ruminants is re-evaluated. (author). 50 refs, 3 figs, 3 tabs