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

Abstract

. 2003. Validating and using the GrassGro decision support tool for a mixed grass/alfalfa pasture in western Canada. Can. J. Anim. Sci. 83: 171-182. 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 1.1 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 on steer production in both continuous and rotational grazing systems using a range of stocking rates from 1.1 to 5.5 steers ha -1 . Les prévisions du gain quotidien moyen, de la masse moyenne de fourrages et de la composition botanique reflètent bien les données réelles. Celles de la digestibilité et de la concentration de protéines sont moins précises et les auteurs fournissent des explications. Les bouvillons utilisés lors de l'essai sur le terrain n'étaient pas arrivés au poids d'abattage au terme de leur mise à l'herbe. On s'est servi du modèle GrassGro pour vérifier l'incidence d'un supplément d'orge servi aux bouvillons durant la paissance. Les résultats indiquent que les animaux auraient pu être amenés à leur poids de finition au pâturage. Selon la simulation, un supplément permettrait de porter la capacité de charge à 2,2 bouvillons par hectare, ce qui s'avère plus intéressant, car on engraisserait deux fois plus d'animaux sans augmenter beaucoup la quantité d'orge fournie. D'autres simulations précisent les conséquences des variations climatiques survenues au cours d'une période de 30 ans (de 1967 à 1996) sur la production de bouvillons dans un régime de paissance continue ou en rotation, avec une capacité de charge allant de 1,1 à 5,5 animaux par hectare. Key words:

Summer-growing perennial grasses are a potential new feed source in the low rainfall environment of southern Australia

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Application of fecal near-infrared spectroscopy and nutritional balance software to monitor diet quality and body condition in beef cows grazing Arizona rangeland1

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Management of Canadian prairie region grazed grasslands: Soil C sequestration, livestock productivity and profitability

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