As indicated previously, dusty and moldy hay is unacceptable for horses. Conventional field dried hay must be 20 percent moisture or less for safe storage. Of all perennial species grown for hay in Pennsylvania, red clover is one of the most difficult to field cure. Today a number of chemical preservatives are being marketed which if properly applied at the time of baling make it possible to bale and store hay safely at moistures up to 25 percent. Research indicates that hay treated with most chemical preservatives is safe to feed to horses as long as no dust or mold is present.
Horses are extremely susceptible to molds, fungi, and other sources of toxic substances in forage.
This is especially a problem with first cutting hay because it is harvested during a period of time when it rains frequently and the weather conditions are less than ideal for hay drying. Always use clean, unmoldy forages when feeding horses. In addition to molds and fungi, some forage species contain chemical compounds that can have negative health effects on horses. Sudangrass and sorghum-sudangrass hybrids contain compounds which can cause muscle weakness, urinary problems and death in severe cases. Older varieties of tall fescue contained an endophyte fungus that could cause severe health problems if horses have only tall fescue to eat during the summer months.