Simulating the influence of stocking rate, sward height and density on steer productivity and grazing behavior

Abstract

A simulation model was written to study how sward characteristics affect steer performance and the grazing behavior of steers. This model, called INTERFACE, simulates grazing behaviour as affected by both horizontal and vertical distribution of forage quality throughout simulated swards. Simulated steers grazed small, rectangular pastures containing a tall fescue monoculture. Horizontally, the pasture was divided into 12 equally-sized sites with the water and mineral source both located in one site. Steers randomly selected a site for grazing. Vertically, the sward was divided into five layers, each of which varied in quality, i.e. proportion of cell wall, nitrogen, minerals or lignin. Results of trial simulations indicated that steers spent more time grazing sites near the water source and progressively less as distance from the water source increased. Grazing time increased as the sward became shorter and more inferior in quality. Although this model simulates diet selection simply as a random process, grazing time comparisons with actual grazing data suggest that this assumption may be adequate. This model can be used to test hypotheses about grazing behavior as influenced by forage quality and sward height.