Prediction of Animal Performance on Bermudagrass Pasture from Available Forage1

Abstract

AbstractBermudagrass [Cynodon dactylon (L.) Pers.] is a major warmseason perennial grass grown on improved pastures in the South. Available forage and its digestibility vary widely in a normal grazing season on bermudagrass pasture. A method is needed to predict steer (Bos sp.) gains from the amount and digestibility of available forage. Five bermudagrass cultivars differing in digestibility were grazed at different grazing pressures to produce four levels of available forage. Forage was classified by concentration of in vitro digestible dry matter (IVDDM) as high (>600 g kg−1 IVDDM), medium (530 to 600 g kg−1 IVDDM), or low ( <530 g kg−1 IVDDM) digestibility. At each level of IVDDM, average daily gain (ADG) of steers was fitted to an asymptotic function of available forage. On high, medium, and low digestibility forages, approximate asymptotic ADG values were 0.94, 0.74, and 0.31 kg, and 68,83, and 89 g forage kg−1 body weight day−1, respectively, were needed to produce the asymptotic ADG values. For steers to maintain their weight on high, medium, and low digestibility forage, 14,18, and 43 g forage dry matter kg−1 body weight day−1, respectively, must be present. Because the quantities of available forage required for maximum steer gains or even for maintenance were far in excess of what the steers could physically consume, it appears that opportunity for selective grazing is necessary.