Ionophores Reduce Impact of Drought Induced Forage Losses

Ionophores reduce impact of drought induced forage losses.  Photo courtesy of Troy Walz.
Ionophores reduce impact of drought induced forage losses. Photo courtesy of Troy Walz.

By Heather DePra, UNL Extension Educator and Bruce Anderson, UNL Extension Forage Specialist

Drought in Nebraska and much of the United States has cattlemen worried about their pasture and forage supply this year. Culling, early weaning, limit feeding hay and/or concentrates, using alternative feeds, or ammoniating low quality roughages are just a few of the options to consider when implementing a drought plan. Another option is to add an ionophore, a common feed additive, into your cattle nutrition program.

Rumensin and Bovatech, commonly known ionophores, are not new to the beef industry. Rumensin was introduced to cattlemen over 30 years ago and has significantly changed the cattle feeding industry by improving feed efficiency and controlling coccidiosis. However, ionophores can also be used in many other phases of beef cattle production. The improvement in feed efficiency when feeding Rumensin actually increases as the forage level in the diet increases. Therefore, ionophores also provide significant benefits to mature cows in dry lot, cow-calf pairs on pasture, and grazing yearlings. As Rumensin is the only ionophore approved for use in mature reproducing beef cows, it will be referred to as the ionophore of choice for the remainder of the article.

The saying “if a little is good, a lot is better” is not true when it comes to ionophores. At undiluted levels, they can be toxic. Horses are especially sensitive to them. The LD 50 (dose at which a product is expected to be lethal for 50% of the population) for Rumensin in horses is 0.6 mg/lb (1.4 mg/kg), equating to an LD 50 of 763 mg for a 1200 lb horse. Although this is over three times the recommended Rumensin dose for cattle on pasture, it is best to keep horses away from products containing Rumensin, especially mineral and pre-mix type products where Rumensin is highly concentrated in a product. The LD 50 for Rumensin in cattle is 12 mg/lb (26.4 mg/kg), equating to 6,000 mg for a 500 lb calf.

Rumensin fed at appropriate levels improves feed efficiency by acting directly on the bacteria within the rumen to shift the bacteria population to a higher percentage of bacteria that are more efficient. That means cattle get more energy out of the same amount of feed when Rumensin is fed. A summary of 24 different forage trials consistently shows an average improvement of 0.2 lbs/head/day in stocker cattle when fed Rumensin at 200 mg/head/day (Potter, et. al, 1986), across a wide range of forage types, growing seasons, and supplementation methods. Similarly, a four trial summary, utilizing mature beef cows fed 50-200 mg/head/day of Rumensin, showed cows maintained the same body weight on 5-10% less feed (NADA 95-735). Therefore, with Rumensin, you can feed the same number of cows with 5-10% less feed or you can feed the same amount of feed and increase the number of cows 5-10%. Keep in mind, the expected improvement in feed efficiency assumes the basic energy and protein requirements of the cattle are being met.

Another benefit to Rumensin is that it prevents and controls coccidiosis, a disease in which protozoa damage the lining of the intestines, cecum, and colon. When consumed by cattle at the appropriate mg/head/day level (at least 0.14 mg/lb of body weight/day, up to 200 mg/head/day for beef cows), Rumensin kills the invading protozoa at several places within the protozoan lifecycle: before the coccidia invade the small intestine, as the protozoa emerge into the lumen of the small intestine, and also in the lumen of the large intestine. Rumensin also reduces the opportunity for reinfection by reducing the amount of new coccidia shed by the animal.

The higher your per head/day feeding costs, obviously the greater your return on the cost of Rumensin. The following are several examples of the cost benefit when implementing Rumensin into your feeding program:

Mature cows in dry lot: Rumensin costs about $0.02/head/day when fed at an intake of 200 mg/head/day. Daily delivery can be accomplished several ways. It can be part of a total mixed ration fed daily, blended into a supplement fed to cows receiving free-choice forage, through a protein cake, or part of a salt-mineral mix. If feed efficiency improves just 5%, Rumensin is cost effective whenever daily feed costs exceed 40 cents/cow. Commonly, dry lot ration feed costs are more than $2.50/cow/day so 2 cents of Rumensin should reduce daily feed costs at least 12.5 cents/cow, resulting in a net gain of at least 10.5 cents/cow/day. For a 100-cow herd, instead of spending $250/day for feed, cost may be reduced to $239.50/day for feed with Rumensin. Plus, feed supplies will last longer or allow you to feed 4 or 5 more cows.

Cow-calf pairs on pasture: For cattle on pasture not receiving supplemental feed, Rumensin can be provided as part of a salt-mineral mix, either as a loose, free choice mineral or in pressed blocks. Rumensin may add up to 3 to 4 cents per day above what the blocks or free choice mineral mixes alone cost. Similar to dry-lotted cows, cows on pasture will utilize the available forage more efficiently, helping maintain body weight (or body condition score) on less forage by increasing the energy value of the forage already being consumed (NRC, 1996). In addition, coccidiosis is controlled in the cows, lessening the chance of calves becoming infected.

Stockers or replacement heifers on pasture: Yearling daily gain on pasture increases about 0.2 lbs/head when Rumensin is supplied by one of the previously mentioned methods. If added Rumensin costs 4 cents/day, the value of the added gain only needs to be greater than 20 cents/pound for this addition to be cost effective. If the value of gain is $1/pound, adding Rumensin will provide a daily net gain of about 16 cents /head, or $24/head during a 150-day grazing season. Replacement heifers on pasture would also be expected to increase average daily gain when fed Rumensin and may also have fewer days to first estrus.

Ionophores are an important tool when managing feed costs for your cattle. Contact your feed consultant or local extension office for more information.

For more UNL Beef information go to