Estrus Synchronization and Pregnancy Rates of Beef Cows Administered Melengesterol Acetate the Ten Days before Estrus Synchronization with Syncro-mate B

treatments the cows were randomly assigned to two groups. One group of cows (n= 281) was fed 0.5 mg of melengestrol acetate (MGA) per head per day for ten days while the other group of cows (n= 257) served as controls. All cows were bled for progesterone concentrations at the beginning of the MGA feeding (d -21), before the SMB treatment, and at the time of artificial insemination (AI). Twenty-eight days after AI, cows in both groups were examined for pregnancy using transrectal ultrasonagraphy. MGA feeding increased (P=.02) synchronization rates in the estrouscycling females; however, MGA feeding did not improve (P>.01) pregnancy rates. In summary, MGA may be used to improve synchronization rates of estrus-cycling females, but the improvement is likely not warranted unless higher pregnancy rates are observed. For example, if the overall pregnancy rate would have been 55%, the improvement in synchronization would have yielded a 4% overall increase in pregnancy rates.