title: Energy and protein metabolism in ewes as influenced by age and dietary protein-calorie ratio.
abstract: A 2 X 2 X 2 fractorial design of treatments was used to study effects of age (20 months or 10 years), dietary energy density (3.0 or 3.5 kcal DE/g) and protein level (8 or 16% crude protein) on energy and nitrogen metabolism in two groups of ewes, with emphasis on efficiency of metabolizable energy utilization. Plasma glucose concentrations were the same for sheep in each age group, regardless of diet; plasma lactate was higher (P less than .03) in plasma of old ewes and decreased (P less than .01) in concentration when dietary energy density was increased. Plasma urea nitrogen was higher (P less than .0001) in ewes fed diets containing 16 vs 8% protein, and plasma ammonia concentrations were higher (P less than .02) in old ewes Dietary energy and protein levels affected digestible and metabolizable energy, but no age-related effects were observed. Nitrogen retention was increased when either energy (P less than .0001) or protein (P less than .003) intake increased. Oxygen consumption was the same for sheep of either age (expressed per kilogram metabolic body weight), while estimated maintenance requirement and heat production were higher for old ewes. Metabolizable energy utilization was lower (P less than .05) in old ewes fed the lower energy density diets than in those fed the higher energy diets. Increasing dietary energy density increased (P less than .05) efficiency of metabolizable energy utilization in old ewes to a level comparable to that observed in young ewes.
mesh_terms: D000375:Aging; D000818:Animals; D001806:Blood Urea Nitrogen; D004044:Dietary Proteins; D004734:Energy Metabolism; D005260:Female; D007773:Lactates / Q000097:blood; D010101:Oxygen Consumption; D012756:Sheep / Q000378:metabolism / Q000502:physiology*
chemical_list: D004044:Dietary Proteins; D007773:Lactates