The body of a pregnant mare produces a biochemical known as dopamine. It occurs naturally throughout the body and affects the functions of glands, organs, muscles, and nerves. Within the endophyte fungus are substances that, in a sense, imprison the dopamine receptors in the mare's system so that they can't function normally. The result is decreased production of both prolactin and progesterone. Prolactin is the hormone that stimulates milk production.
Progesterone is the key hormone involved in maintaining a normal pregnancy.
When the substances in the fungus effectively reduce the normal supplies of these two hormones, the mare fails to produce milk and things go awry within her reproductive system. However, domperidone, when administered, doesn't allow the substances within the fungus to imprison dopamine, and the mare's body is able to produce the appropriate amounts of prolactin and progesterone. N.M. One of the key speakers was Dee Cross, PhD, of Clemson University. Cross was the leading researcher in the development of domperidone for use in pregnant mares. For many years, he told his listeners, veterinarians and mare owners reported reproductive problems in mares grazing tall fescue grass.