monensin sodium, achieved some of the objectives identified by rumen microbiologists and
ruminant nutritionists, at least to a limited extent, and the ban on their use in the European
Union removed their benefits from ruminant livestock producers, prompting research on
replacements. However, targets such as improving fibre digestion and suppressing the bacteriolytic
activity of ciliate protozoa were never impacted substantively by ionophores. Thus,
although the growth-promoting antimicrobial feed additives (GPAFA) ban has increased
interest in feed additives such as probiotics (or more accurately in ruminants, direct-fed
microbials), biological feed additives such as enzymes and plant extracts have the potential
to address targets that differ from those affected by ionophores and/or have other beneficial
impacts.