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To determine to what extent exposure to high ambient temperature and feeding level affect tissue energy metabolism in piglets, regional blood flow and oxidative capacity of tissues were evaluated in sixteen 21.8 +/- 2.8 kg pigs. At 5 weeks of age, littermates were divided into three groups and acclimated to the treatment for 25 days. One group was reared at 33 degrees C and fed ad libitum (33AL, n = 6) while the other two groups were maintained at 23 degrees C and either pair-fed on the basis of the food consumption of their 33AL littermates (23PF, n = 5), or fed ad libitum (23AL, n = 5). Regional blood flow was determined in conscious pigs by injection of coloured microspheres, which were recovered in different tissues after slaughter. Activities of cytochrome oxidase and cytochrome aa(3) content were measured in tissue homogenates of heart, longissimus dorsi and rhomboideus muscles, liver and small intestine. There was decreased blood flow to internal adipose tissue (42 %) and increased blood flow to peripheral tissues (skin, 44 %) and tissues implicated in respiratory evaporative heat loss (diaphragm, 45 %, lungs, 59 %) at 33 degrees C compared to 23 degrees C, which can be viewed as an effective mechanism for increasing heat loss at high temperature. In addition, the concomitant decrease in blood flow (49 %) and slight reduction of oxidative capacities in both muscles at 33 degrees C might contribute to the reduction in thermogenesis, but these effects were also observed when the feeding level was reduced at thermal neutrality (23PF group). In the viscera (intestine, liver), blood flow was decreased in the two groups on a restricted food intake (about 50 % of 23AL), independently of environmental temperature. The results suggest that most of the mechanisms associated with the reduction in energy expenditure during warm acclimation are related to the adaptive reduction in food intake. Experimental Physiology (2001) 86.1, 83-91.

Newborn pigs rely essentially on shivering thermogenesis in the cold. In order to understand the rapid postnatal enhancement of thermogenic capacities in piglets, the oxygen and nutrient uptake of hindquarters was measured in vivo in 1- (n = 6) and 5-day-old (n = 6) animals at thermal neutrality and during cold exposure. The hindquarters were considered to represent a skeletal muscle compartment. Indirect calorimetry and arterio-venous techniques were used. The cold challenge (23 C at 1 day old and 15 C at 5 days old for 90 min) induced a similar increase (+90 %) in regulatory heat production at both ages. Hindquarters blood flow was higher at 5 days than 1 day old at thermal neutrality (26 +/- 3 vs. 17 +/- 1 ml min-1 (100 g hindquarters)-1) and its increase in the cold was much more marked (+65 % at 5 days old vs. +25 % at 1 day old). Oxygen extraction by the hindquarters rose from 30-35 % at thermal neutrality to 65-70 % in the cold at both ages. The calculated contribution of skeletal muscle to total oxygen consumption averaged 34-40 % at thermal neutrality and 50-64 % in the cold and skeletal muscle was the major contributor to regulatory thermogenesis. Based on hindquarters glucose uptake and lactate release, carbohydrate appeared to be an important fuel for shivering. However, net uptake of fatty acids increased progressively during cold exposure at 5 days old. The enhancement in muscular blood supply and fatty acid utilization during shivering is probably related to the postnatal improvement in the thermoregulatory response of the piglet.