This results from the mare's tissues and muscles not being prepared to foal, as well as the foal having a large skeletal structure due to the prolonged gestation. He also pointed out that, often, the foal will fail to properly turn and position itself for foaling. Assuming that the foal is born alive and is up and well, your problems may not be over. He said that, as a result, the foal will fail to get the passive immunity provided in a mare's colostrum, and must receive supplemental colostrum or an antibody infusion, adding to the overall complications. Young horses grazing on endophyte-infected fescue have shown a trend in lower growth rates, sometimes as much as half the rate of comparable yearlings not eating fescue.
More research is needed.
He noted that fescue problems are dose-related. The difficulty is in knowing whether your fescue is endophyte infected or not. Endophytes, which grow inside plants rather than in the outer portions, cannot by seen by the eye, and can only be detected by laboratory tests. Also, the fungus does not adversely affect plant growth, so there's no visible sign of it in the pasture, such as dead plants. The fungus is transmitted only through the seeds, and does not spread from plant to plant or stay in the soil.