An ionophore is a substance that transports ions across a lipid membrane in a cell by combining with the ion, or by increasing the absorptivity or sponginess of the membrane. Ionophores are an old technology that can be used as an antimicrobial, anticoccidial, feed efficient, and growth promotant. The most common examples are Bovatec, Rumensin, and Cattlyst; Bovatec and Cattlyst are FDA-approved to be used in conjunction with Aureomycin. In a livestock setting most mature ruminants receive Rumensin, while young stock tend to be fed Bovatec.
Ruminants are unique as you are often targeting what the “bugs” in the rumen want to eat, not what the ruminant wants to eat. The term “bugs” refers to the wide variety of bacteria, protozoa, and fungi, that are in the rumen and that work to break down the feed ingredients ruminants are ingesting. The bacteria in the rumen produce volatile fatty acids or VFAs (ace-tate, proprionate, butyrate which are listed in order of amount found in the rumen) during the degradation of feedstuffs. VFAs are the products that fuel the animal’s growth and production, i.e. muscle and milk. Different feeds can change the microbial population in the rumen. When fed ionophores, the bacteria population in the rumen shifts from a gram positive bacteria (which produces acetate) to a more gram negative population (increased proprionate). Gram negative bacteria is the goal as proprionate is more efficient than acetate in increasing growth or milk production.
Benefits of ionophores
Due to the changes in ruminal microflora, there are also antibacterial effects that occur in the rumen. Coccidial agents can damage intestines, inhibiting the absorption of nutrients and growth. Ionophores kill coccidia before it can infect the animal. Ionophores form lipid soluble, reversible complexes with cations and facilitate ion transport across membranes, as well as a monensin-electroneutral exchange of sodium and protons. Polyether antibiotics or carboxyl ionophores disrupt ion concentration gradient (Calcium, Potassium, Sodium). This disruption prevents microorganisms from maintaining normal metabolism, thus causing them to expend extra energy for the animal.
Ionophores improve the digestive process of the ruminant, reducing waste products including methane. They decrease the ruminal protein breakdown, which in turn increases protein utilization and decreases ammonia production. With the benefit of increased feed efficiency, producers can realize a better growth rate while seeing less fallout from coccidiosis. Mon-ensin can also reduce the risk of displaced abomasum, clinical ketosis, clinical mastitis, acidosis, and bloat, which is likely due to the animal’s improved energy metabolism.
Ionophores can have toxic effects which are generally a result of improper use and/or mixing errors. They disrupt the normal ionic gradients of cells, which leads to mitochondrial damage and lack of cellular energy. In cattle, improper use or errors can result in cardiac toxicity and muscle degeneration. Ionophores can be lethal to horses, dogs, and other animals. If it doesn’t kill them, skeletal muscle damage and other permanent problems may occur.
While there are many worthwhile advantages to using ionophores, several precautions should be taken. This is a regulated product that is required to be listed on feed tags with the rate of the ionophore in a ton of feed as well as the amount of feed that should be fed to an individual animal. Due to the mechanism of action, animals that are not ruminants are not able to use ionophores and can die following low levels of ionophore ingestion.