Patterns of substrate utilization from birth to weaning

Abstract

AbstractStrategies to reduce the relatively high incidence of death and disease in young animals must be based on an understanding of the particular metabolic requirements in the period from birth to weaning. In this period, substrate availability and the pathways of substrate utilization differ from those of the foetus and of the adult. Metabolic requirements must be met from the energy stores laid down before birth and from the nutrients present in colostrum and milk. The young animal has a large glucose demand and after exhaustion of hepatic glycogen reserves this must be met by gluconeogenesis. Initiation of gluconeogenesis requires concomitant oxidation of fatty acids, either derived from adipose tissue or from the diet. The young animal is particularly susceptible to hypothermia. Non-shivering thermogenesis in brown adipose tissue uses fatty acids to uncouple oxidation from phosphorylation and also as the major oxidative substrate. In addition, non-shivering thermogenesis is dependent on a minimum concentration of circulating glucose. Shivering thermogenesis is initially fuelled by oxidation of intra-muscular glycogen and then primarily by dietary fat. Growth of white adipose tissue by deposition of dietary fatty acids is an important feature of the metabolism of many species before weaning and this may have several survival advantages.