Balances of energy and matter in growing sheep at several ages, body weights, and planes of nutrition

Abstract

Energy, carbon, and nitrogen balances in young sheep (aged 5, 10, and 14 months) given a roughage-concentrate mixture were measured in closed-circuit respiration apparatus. Animals of diverse weight but the same age and vice versa were studied at levels of feeding between half maintenance and ad libitum. Digestibility decreased by 7 units between the lowest and highest feeding level but was not shown to depend on weight or age. Methane production was lower at 5 months of age than subsequently and, in consequence, metabolizable energy decreased from 3.8 kcal/g digestible organic matter at 5 months of age to 3.6 kcal/g at 10 and 14 months. Net availability of metabolizable energy was measured directly in 10-month-old sheep only, and was then 52 and 62% in animals of 44 and 28 kg respectively. Otherwise, storage of metabolizable energy was not found to vary with weight or age. The young sheep had higher maintenance requirements and therefore lower overall efficiency than adults would have, but had higher net availability of metabolizable energy. Neither appetite nor efficiency was depressed by obesity in 14-month sheep. The fraction of energy balance accounted for by protein did not depend on age but varied inversely with body weight. Two obese animals continued to store a large fraction of energy in fat.