FDA’s Center for Veterinary Medicine (CVM) this week issued a statement to clarify regulations regarding use of melengestrol acetate (MGA) in combination with monensin and tylosin added to cattle rations. The statement intends to clear up some confusion as to how feedyards can use MGA, to suppress estrus in heifers, in feeds also containing monensin and tylosin or monensin alone.

Previous approvals had allowed MGA to be combined with monensin and tylosin, and with monensin alone, in the same top dress, called a “common” top dress. But in October 2011, CVM changed the regulations to reflect new supplemental approvals for melengestrol acetate in combination with monensin and tylosin.

CVM states that currently, melengestrol acetate can be combined with monensin and tylosin as a Type C medicated feed only as specified in the Code of Federal Regulations. Accordingly, MGA can only be mixed as a top dress into complete feed containing 10 to 40 grams per ton of monensin and 8 to 10 grams per ton of tylosin at feeding. Likewise, MGA and monensin can only be combined by mixing MGA as a top dress into complete feed containing 10 to 40 grams per ton of monensin at feeding.

CVM summarizes that MGA can only be fed to heifers in confinement for slaughter as a top dress which is then added to medicated feed containing monensin and tylosin, or monensin alone, at feeding. This can only be done on the farm or feedlot, and commercial feed companies cannot manufacture, pack, or ship a complete Type C medicated feed containing a combination of MGA, monensin and tylosin, or MGA and monensin.

For more detailed information, read the full statement from FDA/CVM.