Relationship between Level of Endophyte Infection and Cattle Gains on Tall Fescue

One hundred eighty yearling Holstein steers and heifers grazed a series of 2‐acre tall fescue (Festuca arundinacea Schreb.) pastures over a three‐year period. Pastures were infected with Acremonium coenophialum at levels from 3 to 83%. A significant overall relationship between endophyte infection frequency (EIF) and average daily gain (ADG) was described by the equation: ADG (lb/d) = 1.46 − 0.01 × EIF(%). Seasonal variation existed whereby spring‐summer gains were reduced 0.15 lb/head/d for each 10% increase in EIF, while no relationship existed for fall grazing. Although the relationships between EIF and ADG were significant, low R2 values suggest other factors are involved. Still, the general relationship may be useful for estimating animal performance on tall fescue when EIF is known and for making economic decisions regarding management and renovation of infected tall fescue stands.