HEAT PRODUCTION

Lavoisier and Laplace - 1780Calorimeter for animal use

Latent heat of melting ice80 kcal melts 1 kg ice

Adiabatic jacket - without loss or gain of heat29.6 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 CALORIMETERS1) 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 BMR1. Age2. Sexual state - (ex. estrus)3. Size and surface area4. Undernutrition and overnutrition5. Training6. Climate7. Circadian rhythm8. Altitude9. Sleep10. Body temperature11. Previous diet12. Novelty13. 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 massMouse = 10 watt/kgCow = 0.6 watt/kg

What is best expression MR for large & small animals

Surface area - better than body massWHY?

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 childrenSA = 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 0.75He 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 Symposiumadopted 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 productionIncrease level of nutrition >> decr. LCTALSO - 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 maleDue 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 importantAma 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. HPHP decreases 18-20% spring > summer for Holstein

heifersMight be related to decrease in food intake

Ungulates - cold exposure (chamber) - short or long periods >> incr. RMR

Also occurs naturally - sheep and cattleMay be some relationship - change - feed intake

Also occurs in birdsWhite 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.