MSU Extension Beef

What are ionophores? How do they work?

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.

Goodrich and others summarized the effects of monensin in 1984 using data from 228 feeding trials and 11,274 head of cattle. On average, monensin offered a slight improvement in average daily gain (ADG) 1.6% (2.40 vs. 2.42 lb./day), and larger improvements in feed efficiency (7.5%) by reducing dry matter feed intake (DMI) by 6.4% (19.1 vs. 17.0 lb./day).

In a 2012 Journal of Animal Science publication, Duffield and others conducted a meta-analysis (i.e., summary) on the inclusion of monensin in growing and finishing cattle diets from 64 qualifying scientific manuscripts and research reports (169 research trials) dated back to 1972. Feeding monensin reduced DMI 3.1% (-0.59 lb.), increased ADG 2.5% (0.06 lb./day) and improved feed efficiency 6.4% (-0.53 lb. feed/lb. gain).

Significant sources of variation influenced DMI and feed efficiency across these studies, including: testing multiple inclusion rates or doses (mg monensin/kg. feed), and the inclusion of corn silage in the diet. The monensin dose ranged from 3 to 98 mg. monensin/kg. feed, with an average dose of 28 mg./kg. across all the studies included in the analysis. Feed efficiency improved linearly with increasingly larger doses of monensin included in the diet. Additionally, corn silage inclusion in the diet resulted in a greater improvement in feed efficiency and reduction in DMI, which may be due to the greater inclusion level of fiber in the diet contributed by the corn silage.

Significant change has occurred in the beef industry since the 1970’s. Since the 1970’s, reported feed efficiency has improved 27% for feedlot cattle. This 27% improvement in feed efficiency could be due to multiple factors such as greater inclusion of concentrates or energy in the diet, grain processing, improved ration balancing, improved feed bunk management and possibly cattle genetics. The improvements in feed efficiency due to feeding monensin were greater in the 1970’s and 1980’s, than in the 1990’s and 2000’s (8.1%, 6.4%, 2.3%, and 3.5%, respectively). Therefore, with the use of new technologies, management practices, and current cattle genetics we can expect a more modest improvement in feed efficiency of 2.5 to 3.5% in the current cattle feeding industry when monensin is fed to feedlot cattle.

A meta-analysis of 16 studies investigating the effect of monensin on the rumen VFA profile of finishing cattle was reported by Ellis and others. The mean dose of monensin was 30 mg./kg. of feed, ranging from 0 to 88 mg./kg., with diets averaging 87% concentrate. The equations developed from the meta-analysis revealed the following VFA profile shift in the rumen: decreasing acetate 2.1%, increasing propionate 8.6%, and decreasing butyrate 11.1% when monensin was fed. This VFA profile shift in the rumen creates more efficient energy production, with less energy lost in the form of methane. The change in the rumen VFA profile due to feeding monensin can be expected to be larger with greater forage inclusion in the diet.

A review of scientific literature on the effects of feeding a different ionophore, lasalocid, has shown similar positive effects on feedlot cattle performance. A meta-analysis published in Journal of Animal Science by Gonder and Lean in 2016 demonstrated feeding lasalocid positively altered the rumen VFA profile with a 4.6% increase in propionate and 3.2% and 0.8% decrease in acetate and butyrate, respectively. Across 31 studies, ADG increased 4.0% (0.09 lb./day), feed efficiency improved 5.2% (-0.90 lb. feed/lb. gain), and DMI (-1.3%; -0.24 lb./day) didn’t differ. Interestingly, the greatest improvement in ADG when feeding lasalocid was for cattle over 600 lbs. and fed for 100 days or less.

Ionophore use to control Coccidiosis

Young calves are often susceptible to coccidiosis, a disease caused by protozoan parasites that can be ingested from the environment (e.g., water, feed, ground, other animals). Symptoms of coccidiosis are often characterized by diarrhea, sometimes with the inclusion of blood in the feces, a decreased appetite and depressed appearance, which may lead to reduced performance. Laboratory diagnosis is conducted by counting the number of oocysts shed per unit of feces. However, the severity of coccidiosis symptoms expressed by the calf may not directly translate to the number of oocysts shed. The use of coccidiostats (i.e., lasalocid, monensin, dequinate) can reduce the oocyst shed count in calves compared with untreated controls.

For young calves produced from a dairy production system destined to the feedlot and challenged with coccidia, the inclusion of a coccidiostat in the calf starter feed may not be able to provide a sufficient dose due to low calf starter intake. Therefore, consider including the coccidiostat in the milk replacer as another route of delivery to present calves with an effective coccidiostat dose to control coccidiosis until weaning.

Return on investment

The return on investment (ROI) for using ionophores is quite advantageous for its relatively small inclusion rate in the diet. If we consider feedlot cattle being fed a common midwestern corn silage-based finishing diet for 200 days and the average performance metrics previously mentioned from the scientific literature (ADG ~2%, DMI ~-1%, F:G ~-3%), feedlot cattle fed an ionophore yield approximately $37 per head more than feedlot cattle not fed an ionophore in today’s market. The ROI for including an ionophore in your feedlot cattle diet is about 4.75:1. The cost per head per day for feeding an ionophore will vary on the inclusion rate and feed intake of the cattle. This quick calculation does not take into consideration the benefits of protecting light weight calves against a coccidia outbreak. Therefore, the ROI of feeding an ionophore to your cattle may be even greater.

For more information on ionophores, reach out to Jerad Jaborek, MSU Extension beef feedlot educator, or your regional ionophore sales representative. We recommend following all ionophore feed label directions according to the feed label. For other beef cattle production related inquires, check out the Michigan State University Extension Beef Team website.

This article was originally published in Michigan Cattleman’s Magazine.