Bovatec is the trade name for the ionophore Lasalocid. According to the 2001 Feed Additive Compendium and online at http://www.fda.gov/cvm/FOI/096-298s10202006.pdf, Lasalocid is approved for use to improve feed efficiency and increase rate of gain in cattle in confinement for slaughter. It is also approved for increased rate of weight gain in pasture cattle, including slaughter, stocker, feeder cattle and dairy and beef replacement heifers. Lasalocid is also approved as a control of coccidiosis in the cattle mentioned above. The compendium does not indicate that Lasalocid is approved to feed to mature, reproducing beef cows on pasture or in drylot.
Monensin, an inonphore that has the trade name Rumensin, does have an approval for mature reproducing beef cows on pasture or in drylot.