Energy Expenditure In Animals Research Articles

Preparation of hydrogen from water by reduction with lithium aluminium hydride for the analysis of delta(2)H by isotope ratio mass spectrometry.

An off-line technique is described for the preparation of H(2) from water prior to analysis of delta(2)H by dual-inlet isotope ratio mass spectrometry. H(2) is produced from sample water by reaction with LiAlH(4). This provides a rapid and inexpensive method for the analysis of delta(2)H in small (10 microL) samples of water. Precision was +/- 4.2 to 8.0 (1sigma(n), n = 8) delta(2)H(VSMOW) for samples between 428 and 1500 delta(2)H(VSMOW), +/- 14.5 delta(2)H(VSMOW) for water enriched to 3750 delta(2)H(VSMOW) and +/- 26.0 delta(2)H(VSMOW) for water enriched to 6100 delta(2)H(VSMOW). Accuracy was +/- 1.1 to 4.2 delta(2)H(VSMOW) for water standards from natural abundance to 1000 delta(2)H(VSMOW) (the highest enrichment at which water of accepted delta(2)H is currently available). This method for delta(2)H determination is most appropriate for use with small (<50 microL) samples of high delta(2)H enrichment such as those produced from doubly labelled water studies of small animals. The levels of measurement precision of delta(2)H would contribute 2.6-3.8% to the precision error in estimates of small animal energy expenditure made using the doubly labelled water technique when duplicate analyses are performed.

Quantitative analysis of leptin mRNA using competitive reverse transcription polymerase chain reaction and capillary electrophoresis with laser-induced fluorescence detection.

Leptin, the protein hormone product of the obese (ob) gene, functions in the regulation of appetite, energy expenditure, and reproduction in animals and humans. Since changes in the level of circulating leptin can have marked physiological consequences, it is important to be able to accurately quantify leptin gene expression. Toward this goal, we have constructed a chicken leptin RNA competitor and successfully employed it as an internal standard in the development of a quantitative-competitive reverse transcription polymerase chain reaction (QC-RT-PCR) assay for leptin mRNA. Capillary electrophoresis with laser-induced fluorescence detection (CE-LIF) was utilized for the separation and analysis of chicken leptin target (261 bp) and competitor (234 bp) dsDNA products from QC-RT-PCR assay samples. Leptin amplicons were separated using a DB-1 coated capillary (27 cm x 100 microm ID) at a field strength of 300 V/cm in a replaceable sieving matrix consisting of 0.5% hydroxypropylmethyl cellulose (HPMC) in 1 x TBE (89 mM Tris-base, 89 mM boric acid, 2 mM EDTA, pH 8.3) buffer with 0.5 microg/mL EnhanCE fluorescent intercalating dye. Samples were diluted 1:100 with deionized water and introduced into the capillary by electrokinetic injection. QC-RT-PCR/CE-LIF was used to quantify leptin mRNA in liver and adipose tissue from 8-week-old male and female broiler chickens. This study is the first report of quantitative analysis of leptin gene expression using QC-RT-PCR/CE-LIF.

Analysis of leptin gene expression in chickens using reverse transcription polymerase chain reaction and capillary electrophoresis with laser-induced fluorescence detection

Leptin is a peptide hormone product of the obese (ob) gene that functions in the regulation of appetite, energy expenditure and reproduction in animals and humans. We have developed a technique using capillary electrophoresis with laser-induced fluorescence detection (CE–LIF) for the analysis of chicken leptin (261 base pairs, bp) and β-actin (612 bp) double-stranded DNA products from reverse transcription polymerase chain reaction (RT-PCR) assays. Amplicons were separated using a DB-1 coated capillary (27 cm×100 μm I.D.) at a field strength of 300 V/cm in a replaceable sieving matrix consisting of 0.5% hydroxypropylmethylcellulose (HPMC) in 1X TBE (89 mM Tris–base, 89 mM boric acid, 2 mM EDTA, pH 8.3) buffer with 0.5 μg/ml EnhanCE fluorescent intercalating dye. RT-PCR samples (1–2 μl) were diluted 1:100 with deionized water and introduced into the capillary by electrokinetic injection. Separations were completed in less than 6 min and the total time required per sample, including capillary conditioning, was 8 min. We have applied RT-PCR–CE–LIF to determine the effects of insulin and estrogen treatment on leptin gene expression relative to that of β-actin in chicken liver and adipose tissue. In addition, we have constructed a chicken leptin mRNA competitor (234 bp amplicon) and evaluated it for use as an internal standard in the development of a quantitative-competitive RT-PCR assay. Our findings represent the first reported application of capillary electrophoresis to the analysis of leptin gene expression by RT-PCR.

Influence of torpor on milk protein composition and secretion in lactating bats.

In the pipistrelle bat (Pipistrellus pipistrellus), the metabolic load of lactation is not met to any significant extent by increased food intake or mobilization of body reserves, and aerial foraging accounts for most of the animal's energy expenditure even during lactation. Energy conservation must, therefore, play a critical role in maintaining lactation. The principal mechanism for energy conservation appears to be the bat's ability to enter torpor, but this may itself interrupt milk synthesis and secretion unless the pipistrelle mammary gland is adapted to counteract its effect. The effect of torpor on mammary tissue function was studied in mammary tissue explant cultures prepared in weeks 1-3 of lactation, when milk water yield was 0.20, 0.88, and 0.30 mL/d respectively. Protein synthesis measured by incorporation of radiolabeled amino acids was 44% lower (P < 0.001) in bat tissue explants cultured at ambient temperature (22 degrees C) compared with 37 degrees C. The reduction was similar to that observed in mouse mammary tissue (57%) and was unaffected by stage of lactation. Analysis of explant protein after [35S]methionine labelling showed the majority of proteins synthesised in culture to be milk proteins; it also demonstrated that the decrease in protein synthesis at ambient temperature was a general phenomenon: synthesis of both secretory and intracellular mammary proteins was reduced at the lower culture temperature. The results suggest that bat mammary tissue has no mechanism to counteract the effect of reduced body temperature and that periods of lactational torpor are likely to cause a pronounced diurnal variation in the rate of milk secretion.

Ruminal ammonia concentration and energy expenditure of cattle estimated by the carbon dioxide entry rate technique

AbstractFive ruminallyfistulatedAngus steers (360 (s.e. 15·4) kg) were givenfood to maintain body weight constant: maize silage (TO) at 0·6 kg dry matter (DM) per 100 kg body weight twice a day. After a 15-day adaptation period they were infused continuously (I) for 96 h, with a solution of NaH14CO3 at a rate of 7 to 8 micro Curies (μCi) per h. On the last 2 days of infusion 30 g (Tl) and 60 g (T2) urea, respectively, were placed in the rumen at the end of the morning meal. Spot samples of urine (250 ml) were taken before and 5 h after the morning meal and after at least 24 h of infusion. Thereafter, animals continued with TO for one additional week, in which they were prepared with catheters inserted in salivary ducts and infused for 48 h, as previously described. Eighteen pairs of spot samples of urine and saliva were takenfrom three of thefive steers (369 (s.e. 20·7) kg), over a period of 5 h, after at least 24 h infusion (six per animal). Rate of carbon dioxide (CO2) production was estimated as the ratio USA (specific activity of CO2)from which energy expenditure was calculated (22 kj/l CO2). Silage composition, in situ degradability and ruminal ammonia and pH were measured. In situ degradability in thefirst 6 h was 200 g/kg and ruminal ammonia was in the range of 20·6 to 39·6 mg/l. Ammonia increased rapidly to 394·2 (T1) and 673·9 mg/l (T2) 1 h after addition of urea into the rumen but in 6 h in situ degradability was unchanged. Ruminal ammonia decreased linearly at rates (mgll per h) of89·3 in Tl (R2 = 0·57, s.d. = 21·5) and 151·6 in T2 (R2 = 0·81, s.d. = 23·3). Animal energy expenditure rates were not affected (P &gt; 0·05) by treatment (TO = 15·6, Tl = 15·6 and T2 = 15·8 kj/h per M075). There was no difference (P &gt; 0·05) in CO2 production rate (mllh per kg M0·75) determined from the SA of CO2 from urine (604) or saliva (630) samples. It was concluded that the energy cost associated with detoxification of the excess of ruminal ammonia was of minor importance in terms of total animal energy expenditure and that estimations ofC02 ratesfromsamples ofurine or saliva are comparable.

Thiazolidinediones stimulate uncoupling protein-2 expression in cell lines representing white and brown adipose tissues and skeletal muscle.

Thiazolidinediones (TZD) are PPAR gamma ligands that sensitize tissues to insulin. A cDNA encoding a mitochondrial protein likely to act as uncoupler (uncoupling protein 2, UCP2) has been recently cloned. Since TZD have been reported to increase energy expenditure in animals, we have examined the effects of these drugs on the expression of UCP2 mRNA in cell lines representing white (3T3-L1 and 3T3-F442A) and brown (HIB-1B) adipose tissues and skeletal muscle (L6). Northern blots probed with a mouse UCP2 full-length cDNA showed a mRNA of 1.6 kb both in tissues and the aforementioned cells lines. Within 4 h of exposing these cells to 30 microM darglitazone, there was an increase in UCP2 mRNA which reached a plateau of 5-10 times the basal in about 8 h. In all cells TZDs (darglitazone, troglitazone) were more active than the predominantly PPAR alpha ligands WY-14,613 and clofibrate, or the non-selective ligand linoleic acid. These results indicate that TZDs can stimulate the expression of UCP2 gene probably via PPAR gamma and hence have the potential to increase energy expenditure in adult humans, in whom UCP2 is expressed ubiquitously.

Validation of the labeled bicarbonate technique for measurement of short-term energy expenditure in the mouse.

The energy expenditure of free-living animals has been studied extensively by the doubly-labeled water (DLW) technique. This method provides a reasonably accurate estimate of daily energy needs. However, there is considerable interest in the energy demands of animals over much shorter timescales, for which the DLW technique is less useful. We examined the possibility of measuring the expenditure of small animals over these shorter timescales from the washout kinetics of a bolus dose of 13C labeled bicarbonate. The study involved 19 laboratory mice which were injected either i.p. or s.c. with 0.2 ml of 13C labeled bicarbonate in water. Mice were placed in a standard respirometry system, maintained at different temperatures to precipitate a 3 fold variation in metabolism. Samples of breath were collected from the chamber into vacutainers at one minute intervals for approximately 40 minutes to an hour. Samples were analyzed by admission to a mass spectrometer (VG Optima) via a GC interface which identified and admitted the CO2 peak. The log converted isotope elimination was linear (r2 > 98% in all cases) indicating a single pool was involved. We evaluated the pool size from a dilution series of the injectate in equilibrium with CO2 gas. Conventional compartmental analysis produced an estimate which on average across the 19 individuals provided a reasonable estimate of the CO2 production. Individual estimates were however imprecise and the overall correlation between isotope and calorimeter estimates had an r2 of only 15%. Reasons for this discrepancy are unclear. Nevertheless an empirical model, using the elimination gradient, pool size and route of isotope administration as predictors explained 86% of the variation in CO2 production. Elimination of a bolus dose of 13C labeled bicarbonate provides a useful tool for estimating the energy metabolism of mice over intervals between 15 and 40 minutes.

Energy expenditure of cattle walking on a flat terrain

AbstractA study was carried out to evaluate the effect of horizontal walking upon CO2 production rate by the carbon dioxide dilution rate technique. This was used as an indicator of animal energy expenditure. Two groups of three 18-month-old Aberdeen-Angus steers were assigned to two experiments. Average weights were 290 (s.e. 7·6) kg and 285 (s.e. 1·0) kg for experiments 1 and 2 respectively. Animals were allocated to individual pens and given 5·0 and 4·5 kg dry matter of a mixed diet for experiments 1 and 2 respectively. After a 45-day training period they were assigned to three walking treatments: 0 (T0), 3 (T3) and 6 (T2) km at 3 km/hfor 3 days in a Latin square design (3 × 3). 14C labelled sodium bicarbonate (5·4 μCi/h), diluted in carbonate-bicarbonate buffer sterile solution 0·1 mol/l, was infused for 92 h intraperitoneally with portable peristaltic pumps carried by the animals. The CO2 production rate was calculated as the ratio between the rate of infusion (μCi/h) and the specific activity of CO2 (μCi/ml CO2) in saliva samples, which were taken, in experiment 1, as an average of the day (09.00 to 16.00 h) and the night (16.00 to 09.00 h of the following day). In experiment 2 the day was divided as follows: prior to activity (09.00 to 13.00 h), activity (14.00 and 15.00 h) and post activity (16.00 h). CO2 production rate (ml CO2 per h per kg M0·75) at resting was 817 (412 kj/kg M0·75), increasing during walking to 1·46 of the resting level (T1 and T2, experiment 2) with no differences between the 1st and 2nd h of activity. One hour post activity, the CO2 production rate returned in T2 to the level of T0 but in T2 remained at 1·28 times that of T0. The average CO2 production rate during a complete day or night (experiment 1) was not affected significantly by the activity. Assuming that CO2 production rate during walking is 1·46 of resting (experiment 2) and remains at that level even at lower speeds, it can be estimated that a daily 6 km walk would increase resting energy expenditure from 1·04 when walking takes 2 h, as in this experiment (3 km/h), to 1·11 when the animal spends 6h(1 km/h).

Thermoregulatory Responses of Cold-Acclimated Fat Mice (Steatomys pratensis)

Ten wild-caught fat mice ( Steatomys pratensis ) were acclimated under short photoperiod (10L:14D) for 50 days at 15°C followed by an additional 50 days at 10°C. All the fat mice became torpid at least once during the study, and there was no significant effect of gender or ambient temperature on the number of animals that displayed torpor. There also was no significant effect of gender or ambient temperature on the body temperature of torpid mice at ambient temperatures of 10 or 15°C, although the minimum body temperature recorded (13–15°C) was ca. 5°C lower than that reported in previous studies. The oxygen consumption of torpid animals was slightly higher at 10°C than at 15°C, presumably to prevent a further decline in body temperature. However, the mean duration of torpor was longer at 10°C (19.5 ± 1.5 h, n = 4) than at 15°C (14.5 ± 4.1 h, n = 4), which enabled fat mice to save 50.4 ± 9.5% of the daily energy expenditure of euthermic animals at 10°C, compared to savings of only 39.9 ± 4.5% at 15°C. Therefore, it appears that S. pratensis is capable of modifying the duration of torpor to offset an increase in the cost of torpor at lower ambient temperatures.

Use of the Doubly-Labeled Water Method to Assess Energy Expenditure in Free Living Cats and Dogs

The doubly-labeled water method uses naturally occurring stable isotopes of water (H2 18O and D2O) to assess energy expenditure, body composition and water flux in animals and humans. The technique is relatively noninvasive (a few blood or urine samples over 2 wk) and is performed in free living conditions during a period of between 5 and 20 d. This is the first report of the use of the method in three cats and two dogs. The measured energy expenditure during 11 d was 207 +/- 12 and 263 kJ.kg-1.d-1 for cats and dogs, respectively. These values were 30 and 10% lower, respectively, than NRC recommendations for energy requirement (NRC 1985, NRC 1986). The percentage body fat was 23 +/- 5% in the three cats and 35% in the two dogs used in this study. The water output (urine + breath) was 36 +/- 4 ml.kg-1.d-1 for the cats and 60 ml.kg-1.d-1 for the dogs. Of the water output, 23% (cats) and 17% (dogs) was lost as insensible water loss. The precision and accuracy of the method are discussed in relation to the assumptions made with this technique and by comparison with published values.

Effect of dietary cimaterol on Na+-K+ ATPase activity in rabbit tissues

Cimaterol, a catecholamine analog that acts as a beta-adrenergic agonist, has been shown to have a growth promoting effect in rabbits. Catecholamines are also known to stimulate ion transport in many tissues. The objective of this study was to determine the effect of dietary cimaterol on rabbit tissue Na(+)-K+ ATPase activity. Twelve New Zealand White rabbits, fed either control diet or cimaterol-supplemented diet, were killed at the end of a 35-d feeding trial. Heart, kidney, and liver were weighed, and total ATPase and Na(+)-K+ ATPase activities of these tissues were determined. Cimaterol did not affect liver and kidney weights, but heart weight was significantly increased. Cimaterol increased both total and Na(+)-K+ ATPase activities in heart and kidney but had no effect in liver. These data indicate that increased dietary energy intake and body energy expenditure in cimaterol-fed animals can be attributed, in part, to elevated Na(+)-K+ ATPase activities in heart and kidney.

Energy Expenditure in Moose Calves

We estimated resting heat production in an open circuit respiration chamber for 10 moose (Alces alces) calves during summer and late winter. Heat production measurements did not differ (P = 0.3097) between sexes, but summer measurements (172 kcal/kgBWo 75/day) were significantly higher (P = 0.0001) than those from late winter (117 kcal/kgBWo75/day). Resting heat production estimates for calves were higher than those reported for adult moose. J. WILDL. MANAGE. 55(3):391-393 Ecological metabolism (Moen 1973), which represents the total daily energy expenditure of free-ranging animals, is a useful statistic when predicting nutritional carrying capacity of ranges. Ecological metabolism is generally calculated as the sum of energy costs associated with various activities (i.e., feeding, walking, ruminating, etc.) during a given time period. Renecker and Hudson (1989) used such estimates when they calculated ecological metabolism for adult moose. Seasonal energy metabolism of adult moose was estimated by Regelin et al. (1985), Renecker and Hudson (1989), and Hubbert (1987). Renecker et al. (1978) measured the resting energy costs and thermoregulatory requirements of moose calves during winter, but no comparable information existed concerning the energetic costs in moose calves during summer. Our objectives were to define resting heat production levels of neonatal moose calves during summer and to provide estimates of resting heat production in late winter which supplement early winter estimates provided by Renecker et al. (1978). By combining these data with other energy costs, ecological metabolism and nutritional carrying capacity can be estimated for moose calves. We thank C. J. Pecham, J. S. Bevins, D. C. Johnson, and G. M. Taber for animal care and assistance with metabolism trials. K. B. Schneider, S. R. Peterson, and S. O. Morgan provided valuable editorial comments. This project was a contribution of Federal Aid in Wildlife Restoration, Projects W-22-2 to W-22-5

On the Relation Between Basal and Field Metabolic Rates in Birds and Mammals

Basal metabolic rate (BMR) is widely assumed to be an index of energy expenditure of free-living animals. However, few attempts have been made to check if the assumption is valid. In this study field metabolic rates (FMR) of 58 species of birds and mammals have been compared with their BMRs. FMR tends to increase with increasing body mass slower than BMR, but the difference was significant only in marsupials. A correlation between mass-independent FMR and BMR (residuals from regressions) is very high in eutherians (mainly rodents), but it is weak in birds and approaches zero in marsupials. The assumption of a proportionality between BMR and energy expenditure of animals does not have a sound experi-

Adaptation du métabolisme énergétique des ruminants à la sous-alimentation. Quantification au niveau de l'animal entier et de tissus corporels

Ruminants respond to underfeeding by a progressive adaptation until a new equilibrium between dietary supply and requirements is reached. The resulting drop in maintenance energy requirements originates from a decrease in basal metabolism that depends on the level and duration of undernutrition. These modifications are not totally accounted for by changes in live weight but might be explained by differential changes in individual tissue weight and metabolism. Tissues contribute to whole animal expenditure in a disproportionate manner relative to their weight. Thus digestive tract, liver and muscle masses contribute 5-11, 1-2.5 and 35-50% to live weight but about 16-29, 17-31 and about 16% to whole animal energy expenditure, respectively, because of differences in tissue metabolic activity. Underfeeding results in a decrease in the contribution of viscera to energy expenditure, whereas results on muscle mass are scarce. These changes in contribution are due to changes in tissue mass, nutrient supply (blood flow) and/or in metabolic activity.

Components of energy expenditure in tumor-bearing animals

Single snapshot measurements of resting energy expenditure (REE) suggest that hypermetabolism contributes to cancer cachexia, but tumor impact on total 24-hr energy expenditure (TEE) is unknown. Automated multicage indirect calorimetry was employed to measure daily energy expenditure in adult Buffalo rats ( n = 16) randomized to tumor inoculation or controls. Measurements included baseline REE, activity EE (AEE), thermic response to food (TEF), and TEE. Rats ( n = 16) were randomized. Metabolic measurements, tumor size, and body weight were recorded weekly. Animals were sacrificed at Week 5 for analysis of host and tumor composition. Significant depletion of total lean body mass occurred in TB rats (> 15% wt loss, ANOVA P < 0.001) which inversely correlated with tumor growth ( r = −0.81, P < 0.001). REE, TEF, AEE, and TEE did not change in controls (ANOVA P = n.s.). In TB rats, a 19.5% increase in REE occurred (119.4 ± 3.3 to 138.7 ± 1.8 kcal/kg LBM/day, P < 0.01). TEE remained unchanged (157.3 ± 5.6 vs 152.9 ± 3.6 kcal/kg LBM/day, P = n.s.) due to a 66% decrease in AEE (32.9 ± 3.1 to 10.5 ± 1.7 kcal/kg LBM/day, P = 0.01). TEF did not change (4.7 ± 0.8 vs 5.0 ± 0.3 kcal/kg LBM/day, P = n.s.). Both TB and controls demonstrated a decreased REE in response to a 24-hr fast (7.9% vs 4.8%, P = n.s.). Respiratory quotient decreased in both groups when comparing fed to fasted values: TB (0.86 to 0.76) and controls (0.86 to 0.71), but the decline was greater in controls ( P = 0.04). Tumor-host interaction results in an increase in REE, but continuous measurements of EE indicate that the effect upon TEE may be offset by a decrease in physical activity. During fasting, a normal adaptive decrement in REE was maintained, but conversion to a fat-burning state was impaired in TB rats compared to controls.

The energy costs of walking, carrying and pulling loads on flat surfaces by Brahman cattle and swamp buffalo

ABSTRACTThe extra energy for walking compared with standing still (EW) (J/m per kg live weight) was measured in three Brahman cattle and two water buffalo. Ew was not affected by species or speed within the most comfortable range of speeds (V = 0·6 to 1·0 m/s) but over the whole range tested, Ew = 0·947F + 1·99 (r = 0·66, no. = 61) with average Ew = 2·1 (s.e. 0·06).The extra energy cost of carrying loads while walking (Ec) (J/m per kg carried) was measured using two Brahman cattle, two water buffalo and a pony. Ec was independent of load (up to 70 kg) and speed but was generally lower when loads were placed over the animals' shoulders instead of on their backs. Average values for the cattle, buffaloes and the pony were 2·6, 4·2 and 3·3, respectively.The efficiency of doing work defined as: work done/energy expended was measured in two Brahman cattle and two water buffalo and gave average values of 0·30 and 0·37 respectively for the two species. Efficiency was proportionately about 0·03 higher for animals wearing a collar than when wearing a single yoke but was unaffected by whether the animals wore single or double yokes, by the speed of travel, the size of the load or whether the load was steady or variable.Along with appropriate values for the energetic efficiency of raising body weight when walking uphill, these data are used to derive a factorial equation for estimating the energy expenditure of animals working in the field.

Effects of cimaterol, a beta-adrenergic agonist, on energy metabolism in ob/ob mice.

Cimaterol when added to the diets for 3 or 9 wk stimulated whole animal energy expenditure and brown adipose tissue thermogenic activity comparably in genetically obese (ob/ob) and lean mice; however, ob/ob mice fed diets containing 140 or 280 micrograms cimaterol/kcal failed to increase energy intake as much as lean mice. Consequently, the efficiency of energy retention was actually lower in ob/ob mice fed diets containing cimaterol than in similarly treated lean mice. Cimaterol stimulated skeletal muscle gain in ob/ob mice, although at no point did final hindlimb muscle weight of ob/ob mice equal that of lean mice. Hyperinsulinemia was abolished in ob/ob mice fed diets containing cimaterol even though plasma corticosterone concentrations remained elevated. We conclude that cimaterol has greater effects on energy balance and plasma insulin, but not on skeletal muscle accretion, in ob/ob mice than in lean mice.

Measurement of 2H2O by IR absorbance in doubly labeled H2O studies of energy expenditure.

The energy expenditure of animals in their natural surroundings can be determined by measuring the turnover in body water of isotopes of oxygen and hydrogen. We evaluated the use of infrared spectrophotometry for measuring 2H2O in small (20-microliters) water samples also labeled with 18O. For 2H2O over the enrichment range of 0.1-1 atom%, there was a linear relationship between infrared absorbance and 2H2O enrichment. 2H2O enrichments could be measured with a precision and accuracy of less than or equal to 1%, using this relationship. The presence of 18O in water samples in enrichments of up to 1 atom% had no significant effect on measurement of 2H2O by infrared absorbance. We measured the simultaneous turnover rates of 2H2O and 3H in mice and turtles also labeled with 18O. Our results validated the use of infrared absorbance in doubly labeled water measures of energy expenditure and indicated that the fractionation factors in vivo for 2H2O and 3H do not differ.

Effect of Environmental Temperature on Energy Balance and Thermogenesis in Rats Fed Normal or Low Protein Diets

Rats fed a low protein (9% metabolizable energy) diet and house at 24°C gained less weight and body energy then controls fed a normal (25%) protein diet. Energy intake and expenditure corrected for body size (kJ/(kg0.75·d)] were similar in rats fed the two diets, but energetic efficiency was suppressed in low protein-fed rats, and the thermogenic response to norepinephrine and the activity of brown adipose tissue (mitochondrial GDP binding) were both significantly elevated. Housing at a higher temperature (29°C) suppressed energy expenditure and brown fat activity in animals fed either diet, and gross efficiency was greater in control animals at 29°C than at 24°C but unaffected in the protein-deficient group. The differences in brown fat activity between dietary groups were still apparent at 29°C. The results suggest that thermogenesis induced by feeding low protein diets is not markedly inhibited by a higher environmental temperature.

A Method for the Statistical Analysis of Time‐Energy Budgets

In this paper I outline a method for estimating the sampling variance of estimates of mean daily energy expenditure of free—ranging animals, based on time—energy budgets. This method combines estimated components of variation from laboratory and field observations into a single estimate of the overall sample variance. An approximate confidence region for the mean daily expenditure can be constructed as well. I illustrate these methods by applying them to the energy budget of the Golden—winged Sunbird (Nectarinia reichenowi) originally published by Gill and Wolf (1975). The total sample variance of the mean daily energy expenditure, when that expenditure is estimated from the time—energy budget approach, is a sum of many terms, including the products of the variances of individual variables, the squared estimates of the mean of individual variables, and the products of the estimated means and covariances among the variables. Thus, the estimated sample variance will usually be large. Any biases in estimation will be propagated throughout the calculations, and errors of staggering magnitude can result. Knowlege of the components of total sampling variance and the sensitivity of these estimates to the various sources of bias should aid field biologists in designing time—energy budget studies so that the maximum possible reliability can be achieved.