Rumensin: Health and Production in Dairy Cattle

Dr. Doug Hammon, D.V.M., Ph.D.
USU Extension Veterinarian

Recently the U.S. Food and Drug Administration (FDA) approved Rumensin for use in lactating and dry dairy cows with a claim for increasing milk production efficiency. For several years many in the dairy industry have eagerly anticipated this FDA approval. Rumensin is a feed additive which has been available and approved for use in dairy heifers and beef cattle for many years. Rumensin was first used to increase the feed efficiency of feedlot cattle and later added a label claim for the prevention and control of coccidiosis in dairy heifers and beef heifers, stocker cattle, and beef cows. In addition to increased milk production efficiency, some research has shown additional health and energy balance benefits in dairy cows supplemented with Rumensin.

The following is a brief summary of findings of some recent studies conducted to determine the effects of Rumensin on health and energy balance of dairy cows.

A Florida study determined that Rumensin controlled-release capsules (Rumensin CRC) administered to cows at dry-off significantly increased body condition score at calving in multiparous cows and improved energy balance in first lactation cows during the transition period. Another study from Ontario, Canada showed that Rumensin CRC administered prior to calving significantly improved indicators of energy balance in both the immediate precalving and postcalving periods. A large study using 1317 Holstein cows from 45 farms in the Canadian provinces of Quebec, Prince Edward Island, and Ontario showed a 40% reduction in both abomasal displacement and clinical ketosis, and a 25% reduction in the incidence of retained placenta in cows treated with Rumensin CRC prior to calving. A study conducted in the Netherlands showed a reduction in mastitis rate, decreased rate of non-infectious lameness and improvement in some reproductive measurements in cows fed Rumensin, compared to cows not fed Rumensin. However, another large study conducted in Australia showed no health or reproductive benefits of Rumensin supplementation in dairy cows, although improvements in milk production and energy balance were reported. Some studies indicate improved energy metabolism and a reduction in energy associated health disorders in cows treated with Rumensin around the time of calving. As energy associated disorders are common and costly, Rumensin may be beneficial and cost effective for improving energy balance and for the prevention of retained placenta, ketosis, and displaced abomasums.

As a caution: the concentrated form of Rumensin (Rumensin 80) should not be kept on the farm. It is recommended that Rumensin be added to rations only as a �diluted� premix from your feed supplier, due to the risk of overfeeding and toxicity. Also, Rumensin and other ionophores are extremely toxic to horses, and care must be taken to avoid accidentally feeding it to them. If you have questions or desire further information, contact Doug Hammon ( or (435) 797-1881). ©