The Physiology of Eating and the Energy Expenditure of the Ruminant at Pasture

Abstract

Large areas of the world are marginal lands and extensive grazing of moderately good or poor pastures is the major avenue for producing meat and milk. As the world population increases, the future supply of meat and milk for man would of necessity have to come from the utilization of existing marginal lands in grazing systems. Conventional estimates of the energy required for maintenance have been made with animals housed indoors in respration chambers. Animals at pasture walk longer distances, and usually up gradients and ingest herbage of usually low dry matter content. Consequently, they spend considerably more time eating and foraging for food than conventionally housed animals. These extra muscular activities, over and above those observed indoors, might increase the maintenance energy requirements of animals on range by 25-50%. It is suggested that this increased requirement might be due to the energy cost of eating, walking to graze, and the "work of digestion" done by the gut in handling bulky pasture materials.