By Jerad Jaborek
Ionophores are carboxylic polyether compounds approved for use in beef cattle feed for improved weight gain, feed efficiency, and/or the prevention and control of coccidiosis. Ionophores are a classification of antibiotics. However, ionophores are not used in human medicine, and therefore, are not regulated by the veterinary feed directive (VFD). In the United States there are three ionophores licensed for use: monensin (Rumensin, Elanco; Monovet, Huvepharma), lasalocid (Bovatec, Zoetis) and laidlomycin propionate (Cattlyst, Zoetis).
These ionophores are produced naturally by different Streptomyces bacteria to aid in the transport of different cations (ions with a positive charge) across the bacterial cell membranes. For some bacteria, generally gram-positive bacteria, ionophores that bind to their cell membrane disrupt the membrane potential and energy production of the bacterium, and therefore, reduces their viability in the rumen environment. Therefore, ionophores cause a shift in the rumen microbiome population. Similar to ionophore-sensitive bacteria, ionophores can cause the same disruption to the protozoan parasites (Eimeria bovis and Eimeri zuernii) that colonize the intestinal lining and are responsible for causing coccidiosis. On this basis, monensin and lasalocid are also classified as coccidiostats.
The shift in the rumen microbiome increases the amount of lactic acid utilizing bacteria and reduces the amount of lactic acid producing bacteria and methane producing bacteria. This shift in rumen volatile fatty acid (VFA) production leads to the increased the production of propionate produced by the microorganisms in the rumen and improves overall energetic efficiency for the ruminant. Additionally, the shift in the microbiome reduces the amount of hyper-ammonia producing (HAP) bacteria that aid in protein digestion in the rumen. This reduction of HAP bacteria reduces the contribution of microbial protein production and increases the amount of bypass protein (i.e., rumen undegradable protein; RUP) leaving the rumen to be digested in the small intestine. This can change the ratio of microbial protein versus dietary RUP, more specifically the amino acids, being absorbed by the animal.
Ionophore effects on cattle feedlot performance
Ionophore use in ruminant feed has been approved since 1975. Multiple reviews and meta-analyses have been conducted over the years for ionophores approved in the United States. The results will be summarized here to show their impact on cattle feedlot performance over time.
Source : osu.edu