Ionophores in Dairy Rations

Introduction Ionophores have been used extensively in the beef industry in Canada since 1977. Until recently, there has been no label indication for use of ionophores in lactating dairy cattle. Ionophores are feed additives that alter rumen microbial populations through ion transfer across cell membranes. In Canada, the label warning prohibiting the use of Rumensin premix in lactating dairy cattle was removed in June 1996. Following this, a controlled release capsule containing monensin was approved for use in dairy cattle as an aid to prevent subclinical ketosis in December 1997. In 2004, both Canada and the United States received approvals for the use of monensin in lactating cow diets for improving milk production efficiency. Although other ionophores such as lasalocid and salinomycin are available for use in other cattle, only monensin is currently approved for dairy cows in North America. This paper discusses the production and health benefits of feeding or administering monensin to dairy cattle.