Impacts of Spatial Patterns in Pasture on Animal Grazing Behavior, Intake, and Performance

Control over the quantity and quality of food ingested by grazing ruminants in temperate pasture systems remains elusive. This is due in part to the foraging choices that animals make when grazing from communities of mixed plant species. Grazing behavior and intake interact strongly with the feed supply-demand balance, pasture composition, and grazing method. These interactions are not completely understood, even for relatively simple pasture communities such as a perennial ryegrass (Lolium perenne L.)-white clover (Trifolium repens L.) mixture. When offered a free choice between these species, ruminants exhibit a partial preference for clover compared to grass (about 0.7:0.3) and have a higher intake rate from clover but do not graze to maximize their daily intake of dry matter (DM). When monocultures of grass and clover are offered as a free choice in 50:50 area ratio, animal performance is no different than from a clover monoculture alone. Thus, all of the feeding value benefits of clover are available when only 0.5 of the grazing area is sown to clover. These observations accord with the satiety theory and imply that there are constraints to eating pure clover that animals can overcome by adding grass to their diet, provided their ability to locate and ingest each food is not seriously limited. The challenge for grassland management is to present feed to animals at pasture in ways that allow them to meet their dietary preferences, while also allowing high rates of animal production per hectare.