THE GOOD NEWS: There is no problem with mature horses (geldings and non-pregnant mares) grazing endophyte-infected pastures or consuming endophyte-infected hay. Young growing horses can also consume the infected fescue as the sole source of forage if they receive a mixed grain supplemental diet. There is a study (Auburn) that indicates young, growing horses had reduced growth rates when grazing on a straight (99%+) infected fescue pasture AND received no supplemental feed. Most fescue pastures are typically mixed with some other grasses as well as clover which reduces the level of infestation. Moreover, most horse owners provide some grain to their young horses.
THE BAD NEWS: Yes. Pregnant mares should be removed from infected fescue pastures or stop feeding infected fescue hay 60 to 90 days before foaling. Dr. Dee Cross of Clemson University, a leading researcher in fescue toxicosis, indicates that 30 days is an ABSOLUTE minimum. Mares grazed on fescue infected with endophyte showed the following symptoms of fescue toxicosis: gestation length was increased 27 days, the number of stillborn foals doubled, agalacia (absence of milk secretion after birth) was 100 percent in infected pastured mares, retained placentas were increased more than five times, placental weight and thickness increased, and prolactin and progesterone decreased. Grain supplementation while still on infected pastures or hay was of no benefit, according to Clemson researchers. Recently foaled mares that had grazed pastures infected with fescue (and/or hay) had a higher embryonic death loss subsequently extending length from foaling to maintained pregnancy.
