A. Kalouti and A. Arieli

A trial was conducted in sheep to validate the usage of continuous heart rate (HR) monitoring for the prediction of energy expenditure (EE) in free-living animals. Sixteen Assaff lambs (BW 50 kg) were used. Four lambs were slaughtered at the beginning of the experiment, and the others at the end of the experiment. Carcass body composition was analysed and energy retention was calculated. The 12 lambs were kept on metabolic crates for 84 d. Lambs were blocked into 3 dietary treatments: Group HH was fed a 75:25 concentrates: alfalfa hay (C:A) diet during the entire experiment. Group LH were fed 25C:75A diet during the first 42 d, and then switched into a 75C:25A diet. Group LL received 25C:75A diet during the entire experimental period. Feed was given ad libitum. The experimental period was divided into 4 sub-periods of 21 d. During each sub-period, body weight change, daily intake and feces output was measured. Intake of ME was calculated from NRC (1989). HR was recorded by data loggers during 15 to 17 d. On 18 d oxygen consumption (VO2), using an open circuit mask system, and HR were measured for a period of 15 min, from which oxygen pulse (OP =VO2:HR ratio) was determined. For each sub-period EE was estimated from daily HR measurements and oxygen consumption, calibrated against OP. Direct measurement of EE could thus be compared with the prediction obtained from the difference between ME intake (MEI) and measured energy retention. Average (and SE) intakes of ME were 857 (33), 854 (39), and 805 (42) kJ/metabolic body weight (MBW)-d in HH, LH, and LL, respectively. The respective energy retentions were 194 (23), 233 (27) and 141 (22) kJ/MBW-d (P = 0.06). Overall energy predictability (MEI/(energy retention + EE estimated by the HR method) was 0.957 (n =12; SE 0.024), and was not affected by dietary energy concentration. It is concluded that the HR technique can be used for the estimation of long-term energy expenditure in growing animals.