Escape from the Chamber: Alternative Methods for large Animal Calorimetry

The heart rate method for estimating metabolic rate: review and recommendations

Under most circumstances heart rate (f(H)) is correlated with the rate of oxygen consumption (VO(2)) and hence the rate of energy expenditure or metabolic rate (MR). For over 60 years this simple principle has underpinned the use of heart rate to estimate metabolic rate in a range of animal species and to answer questions about their physiology, behaviour and ecology. The heart rate method can be applied both quantitatively and qualitatively. The quantitative approach is a two-stage process where firstly f(H) and MR are measured simultaneously under controlled conditions and a predictive calibration relationship derived. Secondly, measurements of heart rate are made and converted to estimates of MR using the calibration relationship. The qualitative approach jumps directly to the second stage, comparing estimates of f(H) under different circumstances and drawing conclusions about MR under the assumption that a relationship exists. This review describes the range of studies which have adopted either the quantitative or qualitative approach to estimating the MR of birds, mammals and reptiles. Studies have tended to focus on species, states and questions which are hard to measure, control or define using other techniques. For example, species studied include large, wide-ranging species such as ungulates, marine predators, and domestic livestock while research questions have concerned behaviours such as flight, diving and the effects of stress. In particular, the qualitative approach has applied to circumstances and/or species where it may be hard or impossible to derive a calibration relationship for practical reasons. The calibration process itself can be complex and a number of factors such as body mass, activity state and stress levels can affect the relationship between f(H) and VO(2). I recommend that a quantitative approach be adopted wherever possible but that this may entail deriving a calibration relationship which is practical and applicable, rather than the most accurate possible. I conclude with a series of recommendations for the application and development of this method.

Estimation of the energy expenditure from heart rate measurements in working oxen

The heart rate (fH) and the energy expenditure (EE) of seven Hintenvaelder (Bos taurus) draught oxen and three zebu (Bos indicusj oxen were measured, while the animals were standing, walking and pulling different loads. Linear regressions for all animals relating EE to fH were highly significant (P < 0·001). The standard errors of the estimate expressed as a percentage of the mean EE (PE) ranged from ±6·7% to ±10·5%. Two animals with PE ±13·7% and ±17·1% were beyond that range. One year later, fH and EE were measured on six of the original seven Hinterwaelder oxen while the animals were standing and walking on a treadmill, on the level and at gradients of 3%, 6% and 9%. In the two experiments mean slope and mean intercept of the regressions of EE on fH were not different (P > 0·05). Irrespective of the kind of work (draught work or lifting work),fH allows a reliable prediction to be made of the EE of working oxen.

The energy costs of walking on the level and on negative and positive slopes in the Granadina goat (Capra hircus)

The energy expenditure of six goats averaging 35 (SE 0.3) kg was measured when the animals were standing or walking on a treadmill enclosed in a confinement-type respiration chamber at different speeds (0.167, 0.333 and 0.500 m/s) and slopes (-10, -5, 0, +5 and +10%). The energy costs of locomotion, estimated from the coefficients of linear regressions of heat production (HP) per kg body weight v. distance travelled were 1.91, 2.33, 3.35, 4.68 and 6.44 J/kg BW per m for -10, -5, 0, +5 and +10% inclines respectively, indicating that the energy expenditure of walking over standing changes with slope according to a slightly curvilinear relationship. The energy cost of raising 1 kg body weight one vertical metre was found to be 31.7 J, giving an average efficiency for upslope locomotion of 30.9%. The energy recovered on vertical descent was estimated as 13.2 J/kg per m, indicating an efficiency of the energy recovered above the theoretical maximum.

Heat loss from humans measured with a direct calorimeter and heat-flow meters

1. Heat loss from three men and three women was measured in a direct calorimeter over 2 or 3 h periods and compared with that determined simultaneously from heat-flow meters attached to the skin surface at the waist. The comparisons were made at each of four ambient temperatures, 15, 20, 25 and 30 degrees. Each subject wore a cotton boiler-suit and minimal underwear. 2. Oral temperatures and skin and clothing temperatures on both trunk and forearm were determined, thus enabling the subjects' internal and external insulation to be calculated. 3. Heat loss determined by the meters was lower than that determined by the calorimeter. The difference increased with increase in ambient temperature. 'Meter' heat loss decreased linearly as ambient temperature was raised. 4. It was concluded that heat-flow meters could provide a useful estimate of total heat loss when the evaporative component is low. The estimate might be improved if the subject is calibrated while wearing the meters in a calorimeter over several short periods. Heat-flow meters could therefore be of particular value in sedentary individuals, when the heart-rate method for estimating energy expenditure can be inappropriate.

Estimation of heat production from heart-rate measurements in cattle

1. Heat production and heart rate of seven steers were measured simultaneously using either a calorimetric chamber or head-cage. 2. The relationship between heat production and heart rate for each animal was best described by linear regression. 3. Differences between individual animals made separate 'calibration equations' necessary for each animal. 4. Accuracy of prediction of heat production from heart rate was better than +/- 10% in all instances. 5. It is concluded that frequent measurement of heart rate appears to offer a practical method for estimation of heat production of free-range animals.

A prudent diet for the nation

Nutritional factors in the aetiology of coronary heart disease, maturity-onset diabetes, diverticular disease and dental caries are discussed. Four principles for a prudent diet are suggested, namely: avoid excess intake of energy, increase dietary fibre intake, reduce total fat intake to approximately 30 per cent of energy intake, take a high proportion of fat as the polyunsaturated form.