Estimation of energy intake from heart rate and energy expenditure in sheep under confinement or grazing condition

We studied the feasibility of using heart rate (HR), or energy expenditure (EE), calculated as HR multiplied by 0, pulse the amount of O-2. delivered to the body at every heartbeat - to estimate individual intake of metabolisable energy (MEI) in lambs. HR was automatically recorded every 20 min during 48 h, and averaged daily (HRmean), in eight confined lambs fed with I kg of concentrate (C), 600 g of concentrate and 400 g of vetch hay (CH), or concentrate ad libitum (CC) or grazing lush green alfalfa (A). 0, pulse was measured for 10 min a.m. and p.m., using an open-circuit respiratory system, simultaneously with HR measurements, Dietary treatments and time of measurement did not affect 0, pulse significantly. Diurnal lowest HR (HRmin) was found at night for all treatments, and highest HR (HRmax) was recorded between 1000 to 1200 in all treatments but CC. Diurnal HRmean was lowest in Of and highest in CC (P < 0.04), the other treatments being intermediate. HRmin was the highest in CC (P < 0.02). Rumination was associated with lower HR than grazing, idling being intermediate (P < 0.001). Diurnal HRmean, but not EE, was significantly related with ME intake in confinement (R-2 = 0.17, P < 0.05), or at pasture (R-2 = 0,55, P < 0.01), and not accurately enough for predictive purposes (R.S.D. 100 to 130 MJ kg(-1) BW0.75). This low accuracy was probably more related with large individual variation, and with environmental effects on HR, than with lack of linearity between MEI and HR, because group means of MEI were well related with HRmean or EE (R-2 = 0.99 and R-2 = 0.97, respectively). (C) 2002 Elsevier Science BY All rights reserved.