Melengestrol acetate (MGA) is a synthetic, orally active hormone similar in structure and activity to progesterone. As a feed additive, it is beneficial in suppressing estrus in feedlot heifers. The suppression of estrus reduces injuries due to riding and chasing and helps maintain feed intake. Performance response to MGA is variable and may depend upon: 1) age of heifers being fed; 2) number of sources of heifers fed together; 3) amount of feeding space per heifer; and/or 4) implant effects.
MGA is approved for use in liquid supplements and can be fed as Rumensin and Bovatec. MGA fed with Rumensin or Bovatec and a growth-promoting implant results in only a small additive effect. The approved level of MGA intake is 0.25 to 0.50 mg/head/day, with 0.40 mg the most common dose.
