Q. My yearling stallion has begun his show career in longe line classes. He is beginning to lose concentration and act “studdy” at shows. It was suggested that I put him on Regumate to help control this behavior (as an alternative to gelding). What are the pros and cons? –Jennifer

A. Altrenogest (brand name Regumate) is a synthetic progestin that mimics certain actions of progesterone in horses. The concern for its effect on stallion behavior is probably based on reports that behavior can be modified in some geldings that act aggressive and stallion-like. It is highly unlikely that a similar response can be expected in an intact stallion because testicular production of testosterone and estrogens should completely override the progesterone effect. In other words, it is extremely doubtful that it will work on a stallion.