Endophytic Fungus and Tall Fescue Utilization by Ruminants

Summary Tall fescue (Festuca arundinacea Schreb.) is a high yielding cool season grass currently grown on approximately 14 million hectares in the United States. It is a highly adaptable grass with excellent major compositional characteristics during much of the year: however, performance of cattle grazing tall fescue has been quite variable. Reduced performance, frequently observed during the hot summer grazing period, is referred to as summer syndrome, summer slump, or summer fescue toxicosis. The syndrome is characterized by reduced gains, increased body temperature and respiration rate, excess salivation, long rough hair coat and decreased milk production in cows. Research seeking to identify the anti-quality components of tall fescue has been in progress almost since its introduction as a major grass species in this country. One of the major research accomplishments in the tall fescue area was identification of the endophytic fungus Acremonium coenophialum. The toxin(s) produced by the endophyte-plant relationship are detrimental to cattle performance. Yearling cattle grazing endophyte infected tall fescue during the spring-summer season had decreased gains, increased body temperature and respiration rate, and decreased serum prolactin. Reduced performance was also observed in calves grazing endophyte infected fescue during the late fall. Other reported ill effects were lowered milk production in dairy cows, decreased conception rates of beef cows, and reduced weaning weights of calves nursing beef cows. Seed from endophyte-infected fescue was shown to be very toxic to cattle. Also, the toxin(s) remained biologically active in hay stored for three years. Fractionation of tall fescue extracts have revealed several biologically active compounds, but the toxin(s) remain to be verified in cattle. Endophyte-free tall fescue can be selected for improved nutritive value, yield, persistence, disease resistance, and low diazaphenan-threne alkaloids. Its utilization offers a great potential for improved productivity of cattle consuming tall fescue.