HEAT PRODUCTION Lavoisier and Laplace - 1780 Calorimeter for animal use Latent heat of melting ice 80 kcal melts 1 kg ice Adiabatic jacket - without loss or gain of heat 29.6 kcal heat/10 hours - guinea pig BOMB CALORIMETERS Heat of combustion - fuels, tissues, foods Resulting increase - water temperature x specific heat water x volume water (L) = calories Burns all food >>> final oxidation product ANIMAL / RESPIRATION CALORIMETERS Atwater and Rosa - 1899 2 concentric copper walls Adjusted mean temperature outer wall = mean temperature inner wall NO HEAT FLOW Heat Loss = volume water passing through it, difference in water temperature entering and leaving, specific heat of water DIRECT CALORIMETER : Problems 1) Expensive 2) Size restriction 3) Slow response time - much slower than rate of heat transfer from animal INDIRECT CALORIMETRY Less expensive, convenient Measure oxygen consumed and carbon dioxide Produced Certain assumptions 2 TYPES OF INDIRECT CALORIMETERS 1) CLOSED - CIRCUIT 2) OPEN - CIRCUIT ______________________________________________ CLOSED - CIRCUIT Animal cut off from outside air respirometer - spirometer - manometer Expired CO2 - absorbed by soda lime or ascarite H2O - absorbed by sulfuric acid or drierite OPEN-CIRCUIT INDIRECT CALORIMETRY Breathes air from outside Exhaled air analyzed for volume and content O2 and CO2 Rates of O2 and CO2 consumptions - calculated Collection - respiratory gases Gas tight masks, helmets, hoods, trachial cannulation, chambers FACTORS DETERMINING BASAL OR RESTING MR BMR: Rested, awake, thermoneutral, fasted (may be days for large animals) • Postabsorptive state difficult to achieve. + BMR may vary by 5% Resting MR : Resting in thermoneutral zone - but not postabsorptive • More convenient measurement FACTORS TO EXCLUDE FROM ALL BMR TESTS: 1. Muscular movement 2. Recent muscular activity (1/2 to 1 hour) 3. Food within 12 - 14 hours (problem with ruminants) 4. Strong emotions, noises, discomfort 5. Extremes of Ta 6. Disease 7. Time of day FACTORS TO ACCOUNT FOR IN INTERPRETATION OF BMR 1. Age 2. Sexual state - (ex. estrus) 3. Size and surface area 4. Undernutrition and overnutrition 5. Training 6. Climate 7. Circadian rhythm 8. Altitude 9. Sleep 10. Body temperature 11. Previous diet 12. Novelty 13. Time of year SIZE AND SURFACE AREA Smaller animal has greater heat loss than larger animal Mouse and Cow comparison Mouse has only small fraction of heat produced by cow in watts But when expressed in terms of body mass Mouse = 10 watt/kg Cow = 0.6 watt/kg What is best expression MR for large & small animals Surface area - better than body mass WHY? Rate of heat transfer proportional Surface Area Surface Law: MR proportional to SA (Kleiber) Problem - Actual SA - poorly defined Meeh - 1879 - used 6 adults & 10 children SA = kW2/3 k specific for species Two bodies with same density - SA proportional to 2/3 power of body mass BUT - MR / BW2/3 is significantly correlated with body weight (a problem) Relationship - MR / BW.74 and body weight - insign. Determined by Brody BRODY - KLEIBER DISCUSSION Brody - interspecific value of 0.734 predicted MR wide range - species Rounded off to 0.7 Kleiber - determined 0.756 - rounded down to 0.75 He thought Brody's value too close to 0.67 for surface area. 1935 - National Research Council adopted 0.73 Kleiber - noted that a significant difference between 0.67 and 0.75 seen only over weight range of 9-fold or more. 1964 - European Energy Metabolism Symposium adopted 0.75 for interspecific comparisons Another Factor Age OTHER FACTORS AFFECTING METABOLISM 1. Activity Level Lowest MR - normally during sleep - with anesthetics can drop even lower Birds - standing up >> 40 - 45% increase MR Eating >> 37% increase in MR 2. Plane of Nutrition At rest - heat production and heat loss - highly dependent on mean rate of feed consumption Increase nutrition level >>> increased metabolic rate Sheep - heat production at TNZ directly related to food intake BUT - rate of increase - heat production at cold Ta - not affected by level of feeding Pigs - even sham feeding >> increased heat production Increase level of nutrition >> decr. LCT ALSO - incr. level of nutrition >> decr. UCT Thermal preference also shifted >> lower level AGE MR increases rapidly at first - then a decline Cattle, horses, goats, and sheep - exponential decrease in MR with age Pig - less age-related change with age Birds - TNZ - widens and shifts to a lower range of Ta with age MR increases with age - then declines for many avian species SEX OF ANIMAL In general - female has approx. 10% lower MR than male Due to greater proportion of subcutaneous fat (greater insulation and less heat loss) BUT - not true during production MR of white leghorn layers approx. 50% greater per unit body weight than cockerels Also an increase in dairy cows Due to increased energetic cost of production . CLIMATE - RACE - STRAIN Galvao men (Brazil) - RMR approx. 10% below that of north Americans and Europeans 1. Potential benefit 2. Not sure if due to race or climate 3.BUT - individuals from temperate climate after moving to tropics - MR drops approx. same magnitude Humans - may "adapt" to thermal stress by simply reducing the response Australian aborigines - sleep at Ta below 0°C - between small fires but without shelter They did not shiver but were able to sleep Tb never reached steady-state Very economical Kalahari bushmen - little clothing Ta near 0°C at night Also do not shiver - and let Tb drop Adipose tissue insulation much less important Ama women divers (Korea) Water temperature may fall to 10°C in winter. Oral temperature may fall 2-4°C during dive. Shivering is activated at lower Ta but less intense. Cows - exposed to chronic heat >> decr. HP HP decreases 18-20% spring > summer for Holstein heifers Might be related to decrease in food intake Ungulates - cold exposure (chamber) - short or long periods >> incr. RMR Also occurs naturally - sheep and cattle May be some relationship - change - feed intake Also occurs in birds White leghorn hens - 22 >> 28°C decr. MR at 3 - 12 days Incr. to 35°C >> decr. MR after 4 weeks Also - MR - birds - highest in winter lowest in summer + summer-acclimatized layers have higher UCT than winter-acclimatized layers Pregnancy - human 6th month - pregnancy MR begins to rise and continues until delivery (20% above normal) MR drops after birth by amount = newborn MR • Mother's energy expenditure does not change during pregnancy.