Ionophores are feed additives that alter rumen microbial populations through ion transfer across cell membranes. Although
ionophores have been used widely in the beef industry for improved feed efficiency and control of
coccidiosis, there has been limited use by the dairy industry. In Canada, the label warning prohibiting the use of
monensin premix in lactating dairy cattle was removed in June 1996. Following this, in December 1997, a controlled release
capsule containing
monensin was approved for use in dairy cattle as an aid to prevent subclinical
ketosis.
Monensin may have several advantages for dairy cattle, including improved energy metabolism, increased milk production, and altered milk components. This literature review was primarily conducted in 1996 by using the Agricola and CAB search databases. Other relevant articles published since the search (up to 1998) have been added. This review will provide practitioners with relevant references in the published literature regarding
ionophore use in dairy cattle. It should also give some guidance as to what effects might be anticipated with the use of
ionophores in lactating dairy animals.