Nutrient synchrony in preruminant calves

In animal nutrition, the nutrient composition of the daily feed supply is composed to match the nutrient requirements for the desired performance. The time of nutrient availability within a day is usually considered not to affect the fate of nutrients. The aim of this thesis was to evaluate effects of the time of nutrient availability within a day (i.e. nutrient synchrony) on the protein and energy metabolism in preruminant calves. Two types of nutrient synchrony were studied: (1) synchrony between total nutrient supply and requirements within a day, and (2) synchrony between protein and carbohydrate availability. The studies were mainly conducted in heavy preruminant calves, because those animals have a very low efficiency of protein utilization for growth compared with other farm animals, such as pigs and lambs, allowing a large potential for improvement. Increasing the feeding frequency increased the efficiency of protein utilization in preruminant calves. This was however not detected when short-term measurements of amino acid metabolism (12 h urea production and oral leucine oxidation) were considered. Dietary carbohydrates were almost completely oxidized, unaffected by feeding level, in heavy preruminant calves. Glucose homeostasis improved with increasing feeding frequency. In pigs, an asynchronous availability of glucose and amino acids within a day reduced protein utilization but did not affect fat retention. In preruminant calves, however, an asynchronous availability of glucose and amino acids did not decrease the efficiency of protein utilization but substantially increased fat retention. Separating the intake of protein and lactose over meals inhibited postprandial plasma insulin responses, but increased glucose excretion in urine. Intramuscular fat content and oxidative enzyme activity increased with decreasing nutrient synchrony in an oxidative muscle in calves. Oxidative enzyme activity is not an appropriate indicator of whole-body heat production in growing calves.