Effects of Grazing Intensity and Chemical Seedhead Suppression On Steers Grazing Tall Fescue Pastures.

Tall fescue (Lolium arundinaceum) is the principal cool-season species within pastures of the southeastern USA and is known to have a mutualistic relationship with a fungal endophyte (Neotyphodium coenophialum) that produces the ergot alkaloids responsible for tall fescue toxicosis.  Management of the reproductive growth of tall fescue is necessary, as the seedheads contain the highest concentrations of ergot alkaloids and livestock have been documented to selectively graze these tissues.  Recently, the herbicide Chaparral^™ has been shown to be an effective method to prevent seedhead production in tall fescue pastures while also increasing steer gains at a low stocking rate.  The objective of this study was to compare the efficacy of Chaparral under multiple grazing intensities.  Chaparral (0 and 140 g ha^-1) and two levels of grazing intensity (low: 3300±250 kg ha^-1 & moderate: 2500±250 kg ha^-1) treatments were arranged in a factorial combination as RCBD with three replications. A variable stocking method was used to estimate the carrying capacity (CC) of each treatment with three Angus steers (264±22.3 kg) used as tester animals. The Chaparral-treated pastures contained forage that greater in crude protein (CP), water soluble carbohydrate (WSC), and in vitro digestible dry matter (IVDDM) over the grazing season.  Steers from the Chaparral and low grazing intensity treatments had higher average daily gains (ADG) compared to animals from the control and moderate grazing intensity treatments.  This increase in steer ADG was able to help offset a decrease in the CC for these treatments (116 and 92 fewer steer day ha^-1, respectively), and resulted in no difference (P > 0.60) in total gain per hectare (GPH) between grazing intensities and herbicide treatments.  The effects of these treatments for alleviating symptoms of fescue toxicosis are inconclusive due to the low levels of ergot alkaloids measured during the 2011 grazing season.