not of the cattle.
Ionophores work by inhibiting or depressing the growth of certain rumen
microorganisms. The inhibition of these organisms alters the rumen fermentation
process in several ways:
1) Ionophores improve feed efficiency by changing the types of fatty acids produced
in the rumen and increasing the capture of feed energy during rumen
fermentation with less methane produced. Animal performance is improves due
to increased energy retention during rumen fermentation.
2) Ionophores decease the breakdown of protein in the rumen. Monensin, for
example, has been shown to have a “protein sparing” effect by decreasing
ammonia formation from protein. The decreased breakdown of protein in the
rumen increases the bypass of protein to the small intestines where it can be
better utilized by the animal. This has little effect on performance of feedlot cattle
on high grain diets, but it is important in growing cattle on high roughage diets.
Research with monensin suggests that it works better on low protein diets.
3) Ionophores reduce the incidence of coccidiosis, acidosis, and bloat. Animal
performance improves by reducing these stressors.
4) While ionophores inhibit fiber-digesting bacteria, this is typically not a major
concern because cattle on ionophores are usually on high grain diets. Some
studies have even shown that fiber digestibility was not affected on high
concentrate finishing diets. Nevertheless, using the proper feeding level of
ionophores is particularly important on the forage-based diets common in
Mississippi stocker operations. Feeding excessive levels of ionophores can
reduce fiber digestion on high forage diets.
5) In general, ionophores enhance the absorption of nitrogen, magnesium,
phosphorus, zinc, and selenium.