CIRCADIAN CHANGES IN ENERGY-EXPENDITURE IN THE PRERUMINANT CALF - WHOLE ANIMAL AND TISSUE-LEVEL

A study was conducted using four preruminant calves to determine the c ontribution of portal-drained viscera, liver, and hindquarters to circ adian changes in total energy expenditure, after removing variations d ue to behavioral patterns. Indirect calorimetry and in vivo arterio-ve nous techniques were used. Standing time was longer (P < .01) after th e meals and shorter (P < .01) at night. These variations were associat ed with higher (P < .01) energy cost of standing immediately after the meals and lower (P < .01) ones at night. When these behavioral effect s were removed, total energy expenditure of lying calves was shown to be stable between the morning and evening meal, to increase by 11.5% a nd remained elevated during the 6 h after the evening meal, and to rea ch the lowest values at night. Portal-drained viscera and liver contri buted 32.8 to 53.7% and 29.1 to 32.2%, respectively, to the circadian variations calculated for calves that were always standing. Changes in splanchnic tissue energy expenditure resulted from combined modificat ions in blood flow and O-2 extraction rate. The contribution of hindqu arters could not be clearly established. Overall, portal-drained visce ra, liver, and hindquarters contributed 17.2, 12.8, and 18.0%, respect ively, to total energy expenditure of standing calves. Their respectiv e in vivo metabolic activities averaged 1.08, 2.10, and .25 mu mol of O-2 consumed.min(-1).g(-1) of fresh tissue.