Performance of Cow-Calf Pairs Grazing Baroptima Plus E34 or Kentucky 31 Tall Fescue in Southwest Missouri.

Tall fescue [Lolium arundinaceum (Schreb.) Darbysh.] is the most popular perennial cool-season grass in the United States. It hosts the mutualistic fungus Epichloë coenophiala [(Morgan-Jones & W. Gams) C.W. Bacon & Schardl, comb. nov.], and this mutualism helps the plant tolerate abiotic and biotic stresses. The same endophyte that makes tall fescue persistent also produces ergot-like alkaloids that are toxic when ingested by livestock. Known as “fescue toxicosis,” this syndrome costs the U.S. livestock industry nearly $2 billion annually from reduced weight gain, intake, and calving rate. In response to the negative effects of toxic endophyte-infected tall fescue, researchers developed novel endophyte-infected tall fescue. ‘BarOptima plus E34’ (BO+) is a novel endophyte-infected tall fescue that produces only a small concentration of ergot alkaloids compared to toxic endophyte-infected ‘Kentucky 31’ (KY-31) tall fescue. We compared cattle performance and forage production in BO+ and KY-31 tall fescue pasture systems from cow-calf pairs grazing in Southwest Missouri. In spring, cows grazing BO+ gained 0.73 kg d^-1 more than cows grazing KY-31 (p<0.01). Also, suckling calves in BO+ gained 0.45 kg d^-1 more than those in KY-31 (p<0.01), which led to a 31 kg difference in 205-d adjusted weaning mass (p<0.01). Autumn average daily gain also differed (p=0.03), cows grazing KY-31 lost 0.2 kg d^-1 compared to zero loss for cows grazing BO+. Additionally, cows grazing BO+ achieved 100% calving rate while those grazing KY-31 calved at only 80%. Forage accumulation did not differ (p=0.06) between BO+ and KY-31 over three years. At the end of the grazing season, a hay surplus existed for KY-31 pastures, while those of BO+ ended at a deficit (p<0.01). KY-31 pastures provided 34 more animal grazing days per hectare (p<0.01) than BO+. It is likely the reduced number of grazing days in BO+ pastures resulted from the uninhibited consumption of forage with reduced toxin levels.