Arieli, A., Department of Animal Science, Faculty of Agriculture, Hebrew University of Jerusalem, P.O. Box 12, Rehovot 76100, Israel
Kalouti, A., Wageningen Agricultural University, Wageningen, Netherlands
Aharoni, Y., Agricultural Research Organization, Ramat Yishay, Israel
Brosh, A., Agricultural Research Organization, Ramat Yishay, Israel

An experiment was conducted in sheep to test the validity of the heart rate method as a tool for determining energy expenditure. A comparison was made between assessments of energy expenditure by this method and the comparative slaughter technique. Animals were kept individually in metabolic cages and were fed ad libitum. One group was fed a high-energy diet, comprised of 75% concentrates and 25% alfalfa hay cubes (C diet) for 84 d. A second group was fed 25% concentrates and 75% of alfalfa hay cubes (R diet) for a 42 d, and then switched to the C diet for 42 d. The third group received the R diet cubes for 84 d. Body composition was determined in four animals at the start of the experiment, and in 12 animals at its termination. The entire experimental period was divided into four sub-periods. For each diet, metabolizability and average heart rate were determined for 3 consecutive days. Individual oxygen consumption was determined by the mask technique and the ratio of oxygen consumption to heart rate, the O2 pulse (O2P), was established for each sub-period. The average ratio of energy expenditure values computed from the product of daily heart rate times O2P to those obtained from the difference between metabolizable energy intake and energy accretion derived from the comparative slaughter technique, was 1.067. We concluded that the monitoring of heart rate combined with a repeatable calibration of individual O2P is a reliable and useful method for determining energy expenditure in ruminants. © 2002 Elsevier Science B.V. All rights reserved.