Direct and Indirect Calorimetry, Carbon & Nitrogen Balance Studies

Deals about animal calorimetry and measurement of retention & utilization of energy

1. Direct and Indirect Calorimetry, Carbon &
Nitrogen Balance Studies
Dr. Kaushalendra Kumar, Assistant Professor
Bihar Veterinary College, Bihar Animal Sciences University, Patna
E-mailID:[email protected]

2. ANIMAL CALORIMETRY: METHODS FOR MEASURING HEAT PRODUCTION AND
ENERGY RETENTION
•Calorimetrymeansthemeasurementofheat.
•Measurementofheatproduction&energyretention inanimalscanbequite
complicated,bothinprincipleandinpractice.
•Heatproductionofanimalscanbemeasuredphysically,i.e. directcalorimetry.
•Alternatively,heatproductioncanbeestimatedfromtherespiratoryexchange
oftheanimal,i.e.indirectcalorimetry.
•Respirationchamberscanalsobeusedtoestimateenergyretentionrather
thanheatproduction,i.e.carbonandnitrogenbalancetechnique

3. Animal calorimeter
•Animalsdonotstoreheat,exceptforrelativelyshortperiodsoftime.
•Measurementsaremadeoverperiodsof24hoursorlongeritassumethat
thequantityofheatlostfromtheanimalisequaltothequantityproduced.
(Aisthebasalmetabolism&B&Crepresentheatproductionatmetabolizableenergyintakesof
40MJand100MJ,respectively)

4. Direct Calorimetry
•Heatislostfrombodyprincipallyby radiation,conduction&convectionfrom
bodysurfaces&byevaporation ofwaterfromtheskin&lungs.
•Animalcalorimeterisessentiallyanairtight,insulatedchamber.
•Inearlycalorimeters,sensibleheatlosses measuredinwatercirculated
throughcoilswithinthechamber&thequantityofheatremovedfromthe
chamberthencalculatedfromtheflowrateofwater&thedifferencebetween
itsentryandexittemperature.
•Evaporativeheatlosses measuredbyrecordingthevolumeofairdrawn
throughthechamberanditsmoisturecontentonentryandexit.

5. •Inamorerecenttypeofcalorimeter- gradientlayercalorimeterused.
•Quantityofheatismeasuredelectricallyasitpassesthroughchamberwall.
•Inthiscalorimeter,bothsensible&evaporativeheatlossescanberecorded
automatically.
•However,Animalcalorimetersareexpensivetobuildandearliertypes
requiredmuchlabourtooperatethem,so,presentlyindirectmethodin
practice.
Cont.....

6. Measurement of respiratory exchange using respiration chambers

7. Cont.....

8. Open-circuit type of chamber
•Air drawn through the chamber at a metered rate & sampled for analysis on
entry & exit.
•Thus, CO2 production, CH4 production & O2 consumption can be estimated.
•If conditions for the animal are to be kept normal, very accurate measures of
gas flow and composition are required.
•Modern equipment, based on infrared analysers, open-circuit chambers have
now largely replaced closed-circuit chambers.

9. Cont.....

10. Respiratory exchange measurement by Indirect calorimetry
•The substances oxidisedin an animal’s body, and whose energy is therefore
converted into heat, consist mainly of carbohydrates, fats & proteins.
•The overall reaction for the oxidation of a carbohydrate such as glucose is:
C6H12O6 + 6O2 6CO2 + 6H2O + 2820 kJ
•oxidation of the typical fat such as tripalmitin is:
C3H5(OOC.C15H31)3 + 72.5O2 51CO2 + 49H2O + 3202 kJ

11. •One gram-molecule of O2 occupies 22.4 L at NPT.
•Thus, if animal obtaining all its energy from the oxidation of glucose, then
the utilisationof one litreof O2 would lead to the production of;
2820/(6 * 22.4) = 20.98 kJ of heat &
for mixtures of CHO, an average value is 21.12 kJ/l
•Such values are k/a thermal equivalents of O2 & are used in indirect
calorimetry to estimate heat production from oxygen consumption.
•For animals catabolisingmixtures of fats, the thermal equivalent of O2 is
19.61 kJ/l.

12. •Animals do not normally obtain energy exclusively from either CHO or fat,
as they oxidisea mixture of these & protein.
•So, in order to apply the appropriate thermal equivalent, it is necessary to
know how much of the oxygen is used for oxidation of each nutrient.
•The proportions are calculated from respiratory quotient (RQ).
•RQ is ratio b/w volume of CO2 produced by animal & volume of O2 used.

13. •RQforcarbohydrateiscalculatedas6CO2/6O2=1.0
•RQofthefat(tripalmitin)iscalculatedas51CO2/72.5O2=0.70
•However,proteinisincompletelyoxidisedinanimalsbodybecausethey
cannotoxidisenitrogen&averageamountofheatproducedbythe
catabolismofproteinis18.0kJ/g.
•Oxidationofeachgramofprotein,produced0.77LCo2&used0.96LO2,
givinganRQof0.80.

14. •Heatisproducednotonlywhennutrientsareoxidisedbutalsowhentheyare
usedforthesynthesisofanimaltissues&bearthesamerelationshipto
respiratoryexchange.
•Therelationshipbetweenrespiratoryexchangeandheatproductionis
disturbediftheoxidationofCHO&fatisincomplete.
•Metabolicdisordermayarisesk/aketosis,inwhichFAarenotcompletely
oxidizedtoCo2&H2O,whereas,CandH2leavethebodyas ketonesbodies.
•Incompleteoxidationalsooccursundernormalconditionsinruminants,
becauseanendproductofCHOfermentationintherumenisCH4.
•So,heatproductioncalculatedfromrespiratoryexchangeinruminantsis
correctedforthiseffectbydeductionof2.42kJforeachlitreofCH4produced.

15. •Calculationsexplainedabovemaybecombinedintoasingleequationk/a
theBrouwerequation(DutchscientistEBrouwer):
HP=16.18VO2+5.16VCO2-5.90N-2.42CH4
Where,HP=heatproduction(kJ), VO2=O2consumption(litres),
VCO2=CO2production(litres),N=urinarynitrogenexcretion(g)&
CH4=methaneproduction(litres).
•However,inpoultrytheNcoefficientis1.20(insteadof5.90), because
poultryexcretenitrogenintheformofuricacid,whichismoreoxidisable
thanurea.

16. Measurement of respiratory exchange in unconfined animals
•REcanbemeasuredwithoutananimalchamberifthesubjectisfittedwitha
facemask,connectedtoeitheraclosedoropencircuitfordeterminingeither
O2consumptionaloneorbothO2consumptionandCO2production.
•Thismethodissuitableforshortperiodsofmeasurementbutcannotbeused
toestimateheatproductionwhentheanimaliseating.
•Forlongerperiodmeasurementsofenergymetabolisminunconfinedanimals,
HPcanbeestimatedwithreasonableaccuracyfromCO2productionalone.
•Thelatterismeasuredbyinfusingthe radio-labelledCO2(14CNaHCO3)into
bodyfluidsandsamplingbodyfluidstodeterminethedegreetowhichthe
labelledCO2isdilutedbythatproducedbytheanimal.

17. Measurement of energy retention by carbon & nitrogen balance technique
•Alternativeapproachistoestimateenergyretentiondirectly&tocalculateHP
bydifference.
•Energystoredbythegrowing&fatteninganimalsmainlyintheformof
protein&fat,asCHOreservesofthebodyaresmall&relativelyconstant.
•So,quantityofprotein&fatstoredcanbeestimatedbycarryingoutaC&N
balancetrial–i.e.bymeasuringtheamountsoftheseelementsentering&
leavingthebody&so,bydifference,theamountsretained.
•Theenergyretainedcanbecalculatedbymultiplyingthequantitiesof
nutrientsstoredbytheircalorificvalues.

18. •BothC&Nentersinthebodythroughfood&Nleavesitinfaeces&urine,
however,CalsoleavesthebodyasCH4&CO2.
•Therefore,balancetrialmustbecarriedoutinarespirationchamber.
•ProcedureforcalculatingtheenergyretentionfromC&Nbalancedataisbest
illustratedbyconsideringananimalinwhichstorageofbothfat&proteinis
takingplace.
•Insuchananimal,intakesofC&Nwillbegreaterthanthequantitiesexcreted
&animalissaidtobeinpositivebalancew.r.t.theseelements.
Cont.....

19. •Thequantityofproteinstorediscalculatedbymultiplyingthe Nbalanceby
(1000/160=6.25),asbodyproteinisassumedtocontain160gN/kg.
•Italsocontains512gC/kg&theamountofCstoredasproteincanbe
calculated.Theremainingcarbonisstoredasfat,whichcontains 746gC/kg.
•Theenergypresentintheproteinandfatstoredisthencalculatedbyusing
averagecalorificvaluesforbodytissue.
•TheadvantagesoftheC&NbalancetechniquearethatnomeasureofO2
consumption(orRQ)isrequired.

20. Measuring energy retention by comparative slaughter technique
•Energy retention can be measured in feeding trials by estimating the energy
content of the animal at the beginning & end of the experiment.
•In this method-dividing the animals into two groups & slaughtering one
group of animals at the beginning of the trial.
•The energy content of the slaughtered animals is then determined by bomb
calorimetry (samples taken either whole, minced or body tissues).

21. •Arelationshipisobtainedb/wtheliveweightofanimals&theirenergycontent
&usedtopredicttheinitialenergycontentofanimalsinthesecondgroup.
•Thelatterareslaughteredattheendoftrial&treatedinthesamemanneras
thoseininitialslaughtergroup&energygainedcalculatedbydifference.
•Thecomparativeslaughtermethodrequiresnoelaborateapparatusbutis
expensiveandlaboriouswhenappliedtolargeranimalspecies.
Cont.....

22. THANKS
25-04-2020 Kaushalendra Kumar, BVC, BASU, Patna 22
Discussions……………….…………..
Questions, if any…………………??