Nutrition of ruminants is dominated by the microbial fermentation that occurs in the
foregut. This fermentation enables ruminants to make maximal use of forages that cannot
be used to feed pigs, poultry or humans. This fermentation could be improved in many
ways, such as by improving fibre digestion, decreasing protein degradation, and/or inhibiting
methane emissions which, if modified, might increase efficiency of ruminant livestock
production and lessen impacts of animal production on the environment. Because ruminal
digestion is entirely microbial in nature, it is subject to modification by selective antimicrobial
agents, including antibiotics and ionophores. Ionophores, the best known of which is