Manipulation of the equine estrous or heat cycle is important for many farms with brood mares.  This is especially important for farms that are involved in artificial insemination and embryo transfer. One of the primary drugs involved in manipulating the equine heat cycle is prostaglandin F(2 alpha) and the only approved drug in horses of this type is Lutalyse. Lutalyse is a natural prostaglandin in contrast to the similar drug cloprostenol that is a synthetic. As a natural prostaglandin, side effects can occur in mares given Lutalyse such as minor colic and sweating. A recent study was performed to determine if a lower than recommended dose of Lutalyse would be effective in mares and potentially decrease side effects and decrease drug cost. North Carolina State used 11 horses and gave some horses the normal dose of 2 cc or 10 mg, some of the horses ½ cc or 2.5 mg, and some horses ¼ cc or 1.25 mg. These were all single injections and results indicated all dosages caused all the mares to come into heat following the injections. So this study shows that 1/8 of the recommended dose can be just as effective as the full dose. 

Although the study did not look at side effects, I would suspect that there would be less side effects with the lower dose as well as a lower cost. Another recent study showed that Lutalyse is also effective if you give only 1/10 cc of the drug twice in a 24-hour period. Although this is even less of the drug, it is cumbersome for most owners or farm managers to have to treat the mares 2 days in a row. The one single injection of ¼ cc Lutalyse instead of the recommended 2 cc is more user friendly and is really something to consider for the spring breeding season.