Validating and using the GrassGro decision support tool for a mixed grass/alfalfa pasture in western Canada

This paper presents predictions of pasture composition and liveweight gain of steers using the GrassGro simulation model. Predictions are compared with field data measured during a 4-yr experiment at Brandon, Manitoba, in which steers grazed alfalfa (Medicago sativa)/grass (Bromus biebersteinii and Psathyrostachys juncea) pastures at I.I and 2.2 steers ha^-1 in continuous or rotational grazing systems. The predictions of average daily gain, mean forage mass and botanical composition were found to accurately reflect the field data. Predictions of digestibility and protein were less accurate and reasons for this are discussed. Steers from the field trial were not considered finished for slaughter directly off pasture. GrassGro was used to examine the effects of feeding a barley supplement to the steers while at pasture. The results indicated that all steers could have been finished at pasture. Simulation indicated that supplementation at pasture makes the stocking rate of 2.2 steers ha^-1 more attractive because twice the number of steers could be finished with little additional requirement for barley supplement. Further simulations provided information on the effects of climate variations during a 30-yr period (1967-1996) on steer production in both continuous and rotational grazing systems using a range of stocking rates from I.I to 5.5 steers ha^-1.