MGA is not currently approved for use to synchronize estrus in mature beef cows on pasture. Even if it were available for use, the MGA-PG system would be difficult for most producers to use in their spring-calving cow herds because of the length of time the protocol demands and in most states cows will be or are about to begin grazing cool-season grasses. MGA-PG protocol to synchronize estrus in heifers works extremely well.