temperature-humidity index values and their significance

56 V. GANTNER et al.: Daily production of dairy cattle, Mljekarstvo 61 (1), 56-63 (2011)

Introduction

Heat stress could be reason of the significantincrease of production cost in the dairy industry.Armstrong (1994)noticed that the relativedailycows’ production is constant when temperaturesare lowandmedium,whileafterpassinga thresh-old,startstodecrease.Therateofdeclineincreaseswithrisingtemperatures.Expositionofdairycattletohighambienttemperatures(Ta),highrelativehu-midity(RH)andsolarradiationforextendedperi-odsdecreasetheabilityofthelactatingdairycowto

Vesna Gantner1*, Pero Mijić1, Krešimir Kuterovac2, Drago Solić3, Ranko Gantner1

1PoljoprivrednifakultetuOsijeku,SveučilišteJ.J.StrossmayerauOsijeku,TrgSvetogTrojstva3,Osijek,Hrvatska

2Agrokord.d.,TrgD.Petrovića3,Zagreb,Hrvatska3Hrvatskapoljoprivrednaagencija,Ilica101,Zagreb,Hrvatska

Received-Prispjelo:06.11.2010.Accepted-Prihvaćeno:12.01.2011.

Summary

Theobjectivesofthisstudyweretodeterminethemicroclimaticconditionsinstablesinthreeclimacticregions(East,Mediterranean,andCentral)ofCroatiaaswellastoevaluatetheeffectoftemperature-humidityindex(THI)valuesonthedailyproductionofdairycattle.Withthatpurpose,1675686test-dayrecordscollectedfromJanuary2005untilApril2010wereextractedfromHPA(CroatianAgriculturalAgency)database.ForestimationoftheeffectofTHIondailyproductionofdairycowsfixed-effectmodelthattookintoaccounttheeffectsoflactationstage,breed,calvingseason,measuringseason,andTHIgroup(T1-THI≤72;T2-THI>72)wasused.Modelwasappliedtoeachclassofparity (P1,P2,P3,P4andP5)andregion.During theanalysedperiod, thehighestmonthly averagesof ambient temperatureweredetermined inMediterranean region, thehighestmonthlyaveragesofrelativehumiditywereobservedinCentralregion,whilethehighestmonthlymeanvaluesoftemperature-humidityindex(THI)weredeterminedinMediterraneanregion.HeatstressconditionsindicatedwithmeandailyvaluesofTHI>72weredeterminedduringspringandsummerseasoninallanalysedregions.Absenceofheatstressconditionsduringautumnandwinterseasonalsocharacterisedallthreeregions.Highlysignificant(P<0.01)decreaseofdailymilkyieldaswellasofdailyfatandproteincontentduetoenhancedTHIwasobservedinallcowsregardlesstheparityclassandinallthreeclimaticregions.Furthermore,themostdeteriorateeffectofheatstresswasobservedinEastregion.Duringheatstressperiod,withtheaimofminimizationoftheeffectsofheatstress,itisnecessarytoregulatemanagementstrategiesinthedairyherd.

Key words: dairycattle;dailyproduction;temperature-humidityindex

Originalscientificpaper-Izvorniznanstvenirad UDK:637.112

Temperature-humidity index values and their significance on the daily production of dairy cattle

*Corresponding author/Dopisni autor: E-mail: [email protected]

disperseheat.Atthesametime,lactatingdairycowscreatealargequantityofmetabolicheat.So,accu-mulated andproducedheat joinedwithdecreasedcoolingcapabilityinducedbyenvironmentalcondi-tions,causesheatstressintheanimals.Finally,heatstressinducesincreaseofbodytemperature.John-son(1980)observedthatwhenthebodytempera-ture is significantly elevated, feed intake,metabo-lism,bodyweightandmilkyieldsdecreasetohelpalleviatetheheatimbalance.Johnsonetal.(1962)determinedthatwiththeterminationofthehotsea-son, inhigh-producingcows, theproductivitydoes

V. GANTNER et al.: Daily production of dairy cattle, Mljekarstvo 61 (1), 56-63 (2011) 57

not completely return to normal since the energydeficitcannotbefullycompensated.Thepermanentdropinthecurrent lactationisproportionaltothelengthoftheheatstress.Thetemperature-humidityindex(THI)couldbeusedtodeterminetheinflu-ence of heat stress on productivity of dairy cows.MilkproductionisaffectedbyheatstresswhenTHIvaluesarehigherthan72,whichcorrespondsto22°Cat100%humidity,25°Cat50%humidity,or28°Cat20%humidity(DuPreezetal.,1990a).Johnson(1980)reportedthat,whenTHIreaches72,milkproductionaswellasfeedintakebeginstodecrease.Theamountofmilkyielddecreaseduringthe summerperiod incomparisonwith thewinterperiodforHolsteincowsabout10%to40%(DuPreezetal.,1990b).UnderMediterraneanclimaticconditions,milkyielddropsby0.41kgpercowperdayforeachpointincreaseinthevalueofTHIabove69(Bouraouietal.,2002).Besidechangesinmilkyield, heat stress could also cause changes inmilkcomposition,somaticcellcounts(SCC)andmastitisfrequencies(Rodriguezetal.,1985,DuPreezetal.,1990b).

Theobjectivesofthisstudyweretodeterminethemicroclimaticconditionsinstablesinthreecli-macticregionsofCroatiaaswellastoevaluatetheeffectoftemperature-humidityindexvaluesonthedailyproductionofdairycattle.

Material and methods

Datasets

Foranalysisofvariabilityofmicroclimaticcondi-tionsinthestableaswellastheirsignificanceonthedailyproductionofdairycattleinCroatia,1675686test-dayrecordscollectedfromJanuary2005untilApril2010on8273dairyfarmsallaroundCroatiawere extracted from HPA (Croatian AgriculturalAgency)database.MilkrecordinginCroatiaoccurs

accordingtothealternativemilkrecordingmethodeveryfourweekswhen,dependingoftheparticular-lyfarm,theHPAcontrolassistant(A)orthefarmer(B)measuresmorningoreveningmilkyield,notesinitialtimeofcontrolmilkingandinitialtimeofpre-viousmilking,and,foranalysisofmilkcomposition,takesmilksamplefromeachlactatingcow.Foranal-ysisofmilkfat,proteinandlactosecontentMilkoS-can133Bwasused.Theintervalbetweensuccessivemilking,requiredforprojectionofdailyvalues,wascomputed as the time from the beginning of pre-viousmilking to the beginning of controlmilking.Dailyproductionofmilkyieldandcomponentswasprojectedusingprojectionparametersestimatedinauthors’earlierresearch(Gantner,2008).Logicalcontrol of productiondatawas performed accord-ingtoICARstandards(2003).Theyieldsrecordedafter the500th lactationdaywasdeleted fromthedataset.

Accordingtotheparity,cowsweredividedintofive classes that are heifers (P1), cows in secondlactation(P2),cowsinthirdlactation(P3),cowsinfourth lactation (P4), and cows in fifth andhigherlactations(P5).VariabilityofanalyzedtraitsinregardtoparityclassesisshowninTable1.

Accordingtothetestdate,fourmeasuringsea-sonsubgroupswerecreated(S1-spring-includingtheperiodfromApriltillJune;S2-summer-includ-ingtheperiodfromJulytillSeptember;S3-autumn-includingtheperiodfromOctobertillDecember;and S4 -winter - including the period from Janu-ary tillMarch).Cowsweredivided in two calvingseasonsubgroupsregardingthecalvingdate(C1andC2 that include animals calved in spring/summerand autumn/winter season). In accordance to thegeographicalandclimaticcharacteristicsofCroatiathree different regionswere formed, namelyEast,Mediterranean, and Central region where 2795,1980, and 3500 respectively dairy farms were in-cludedinresearch.

Table 1. Descriptionofdatasetusedforanalysis(n=1675686)

Parameter

Parity

P1 P2 P3 P4 P5Dailymilkyield,kg 16.62±6.69 17.73±7.84 17.89±7.93 17.34±7.54 15.93±6.79

Dailyfatcontent,% 4.23±0.91 4.25±0.95 4.22±0.95 4.17±0.94 4.09±0.92

Dailyproteincontent,% 3.47±0.48 3.50±0.49 3.47±0.48 3.45±0.47 3.44±0.46


The temperature and the relative humidityin stablewere recordedateachmilking.Thedailytemperature-humidityindex(THI)valueswerecal-culatedusingtheequationbyKibler(1964):

THI=1.8Ta-(1-RH)(Ta-14.3)+32 (1)

where:

Ta - measured ambient temperature in °C, RH -relativehumidityasafractionoftheunit.Accord-ingtothevalueofthetemperature-humidityindex(THI),twoTHIsubgroupswerecreated(T1whereTHI≤72;andT2whereTHI>72).

For estimation of the effect of temperature-humidityindex(THI)ondailyproductionofdairycowsfollowingfixed-effectmodelwasused:

yijkl=μ+b1(d/305)+b2(d/305)2+b3ln(305/d)+

b4ln2(305/d)+Bi+Cj+Sk+Tl+eijkl (2)

where:

yijkl=predicteddailyperformance(yieldorcontent),

μ=intercept.

bi=regressioncoefficientsofAliandSchaefferlacta-tioncurve(1987),

d=lactationstage(days),

Bi=effectofbreed(i=Holstein;Simmental),

Cj=effectofcalvingseason(j=1-spring/summer;2-autumn/winter),

Sk = effect of measuring season (k = 1 - spring;2-summer;3-autumn;4-winter),

Tl=effectofTHIgroup(l=1-THI≤72;2-THI>72),

eijkl=residual.

The significance of differences between themeansofthedailymilkyield,aswellasbetweenthemeans of the daily fat and protein contentwithintheTHIclassesinregardtoparityclassesbyclimaticregionswastestedwithScheffetest.Forthestatisti-calanalysisandthefiguresdrawingtheSAS/STATpackagewasused(SASInstituteInc.,2000).

Results and discussion

Variationsintheambienttemperature(Ta,oC),relative humidity (RH, %), and the temperature-humidityindex(THI)inthestablenotedduringthemeasuringmonthsforanalysedregions(East,Medi-terranean,Central)arereportedinTable2.

Comparing themonthly averages ofmicrocli-matic parameters in analysed regions, highest am-bienttemperaturesweredeterminedinMediterra-nean,whilehighestrelativehumiditywereobserved

Table2.Microclimateconditionsinthestablesduringmeasuringmonthsinaccordancetotheregions(East,Mediterranean,andCentral)

Month/Season

Region/Parameter

East Mediterranean Central

Ta,°C RH,% THI Ta,°C RH,% THI Ta,°C RH,% THI

I./S4 7.5±4.3 69.5±9.8 47.5±6.6 10.3±4.7 70.7±9.6 51.7±7.1 9.6±4.5 73.8±8.7 50.5±6.9

II./S4 8.1±4.6 67.5±9.7 48.4±7.0 11.2±4.9 68.6±9.7 53.1±7.2 10.3±4.5 71.9±8.7 51.6±6.9

III./S4 10.2±4.7 67.1±9.9 51.6±7.4 13.3±5.1 66.6±9.9 56.2±7.3 12.1±4.8 69.4±9.1 54.4±7.2

IV./S1 13.8±5.2 66.4±9.3 56.9±7.8 17.0±5.1 64.0±9.4 61.5±7.2 16.1±4.8 66.9±4.8 60.3±7.0

V./S1 17.6±5.8 65.5±9.8 62.5±8.5 20.4±5.1 65.5±9.7 66.6±7.4 19.8±5.1 67.5±9.5 65.8±7.5

VI./S1 20.4±6.1 67.4±9.7 66.7±9.0 23.3±5.2 67.7±9.2 70.9±7.8 22.5±5.1 68.9±9.5 69.8±7.6

VII./S2 23.1±6.1 66.1±9.9 70.6±8.8 24.9±4.7 68.6±9.5 73.5±6.9 23.9±4.9 68.7±9.8 71.9±7.3

VIII./S2 21.7±5.8 66.2±9.9 68.6±8.3 23.5±4.7 68.6±9.6 71.4±7.1 22.9±4.5 69.6±9.1 70.7±6.9

IX./S2 18.8±5.6 66.6±9.8 64.3±8.0 20.3±4.7 69.8±9.3 66.7±7.1 19.5±4.7 70.9±8.8 65.5±7.1

X./S3 14.6±5.4 69.6±9.7 58.1±8.1 17.0±4.9 70.1±9.0 61.8±7.3 15.9±4.7 71.9±8.5 60.1±7.2

XI./S3 10.9±5.1 69.9±9.4 52.2±7.8 13.2±4.9 70.5±9.8 56.1±7.4 12.5±4.5 72.6±9.0 55.0±6.9

XII./S3 8.4±4.8 70.5±9.8 48.7±7.4 11.2±4.7 72.1±9.6 53.1±7.1 10.3±4.6 74.1±8.6 51.6±7.0

Ta-ambienttemperature(°C);RH-relativehumidity(%);THI-temperature-humidityindex


in Central region. In Mediterranean region werealsodeterminedthehighestvaluesoftemperature-humidityindex(THI).Theseverityofheatstressiscorrelatedtobothambienttemperatureandhumid-ity level. The bovine thermal comfort zone is -13°C to+25 °C.Within this temperature range, theanimalcomfortisoptimal,withabodytemperaturebetween38.4°Cand39.1°C(LefebvreandPla-mondon,2003).Above25°C,andeven20°Cforsomeauthors,thecowsuffersfromheatstress: itshealth status and production performance are af-fected.Berman(1968)determinedthatforlactat-ingdairycowstheambienttemperaturesabove25°Care associatedwith lower feed intake,drops inmilkproduction and reducedmetabolic rate.Ber-manet al. (1985)noticed that theupper limitofambienttemperaturesatwhichHolsteincattlemaymaintainastablebodytemperatureis25to26°C,andthatabove25°Cpracticesshouldbeinstituted

tominimize the rise inbody temperature.Bianca(1965)determineddecrease in dailymilk yield ofHolstein, JerseyandBrownSwisscows inamountof3,7and2%ofnormalatatemperatureof29°Cand40%relativehumidity.Increaseofrelativehu-midityto90%inducesadditionaldecreaseofmilkyieldfor31,25,and17%ofnormalyield.Useofatemperature-humidityindexisaonewaytomeas-urethecombinedeffectoftemperatureandhumid-ity.AmeandailyTHIinvalueof72isconsideredtobethecriticalpointatwhichmilkyieldisreduced(Johnson,1987).IncreasingTHIintherangeof71to81reducedthemilkyieldandintakeoffeedandwaterfordairycows(Johnsonetal.,1963).Theef-fectwasgreatestwhenTHIexceeded76.DuPreezetal.(1990b)statedthatmilkproductionisaffectedbyheatstresswhenTHIvaluesarehigherthan72,whichcorrespondsto22°Cat100%humidity,25°Cat50%humidity,or28°Cat20%humidity.

Figure2.Averagetemperature-humidityindexesduringtheautumn(C)andthewinter(D)season

Figure1.Averagetemperature-humidityindexesduringthespring(A)andthesummer(B)season


Mean daily THI values during spring (Figure1A)andsummer(Figure1B)seasonwerehighestinMediterraneanregionwere,during15daysinspringand38days insummer,meandailyTHIvalueex-ceededcritical(72)indicatingheatstressconditions.Lowest frequency of days with heat stress condi-tionswere observed inEastern region.Absence ofheatstressconditions(THI<72)duringautumnandwinterseasoncharacterisedallthreeregions(Figure2Cand2D).

Effect of exceeded THI on daily milk yieldandcomponentsinrelationtoparityclassesandcli-matic regions are shown in table 3.Highly signifi-cant (P<0.01)decreaseofdailymilk yielddue toenhancedTHIwasobserved inheifers in all threeregions.Thehighestamountofdailyloss(>0.9kg/day)wasdeterminedinheifersbreedinEastregion.RegardingtheeffectofTHIvalueabovecriticalondailyfatandproteincontentinheifercows,highlysignificant(P<0.01)decreasewasobservedinallan-alysedregions.Furthermore,incowsinsecondlac-tationhighlysignificant(P<0.01)decreaseofdailymilkyieldaswellasofdailyfatandproteincontent

inducedbyheatstressconditionswereobservedinallregions.Highlysignificant(P<0.01)decreaseofanalysed productive parameters were also deter-minedinoldercowsinallclimaticregions,whilethemostdeteriorateeffectofheatstresswasobservedinEastregion.

Deteriorate effect of exceeded THI on dailymilkyields andcomponentswerealsoobserved inother studies. Ingraham (1979) estimated thatmilkyieldreductionwas0.32kgperunit increasein THI. Schneider et al. (1988) observed thatheat stressed dairy cows in one chamber experi-ments consumed less feed (13.6 vs. 19.4 kg/day),morewater(86.0vs.81.9l/day)andproducedlessmilk(16.5vs.20.0kg/day)thancowsinathermalneutralenvironment.McDowell(1976)suggestedthatmilkproduction is reducedby15%accompa-niedbya35%decreaseintheefficiencyofenergyutilizationforproductivepurposes,whenalactatingHolsteincowistransferredfromanairtemperatureof18to30°C.Johnsonetal.(1963)reportedthatthemilkyieldandtheDMI(drymatterintake)ex-hibited significant declines (by 1.8 and 1.4 kg for

Table3.LsmeansofproductionparametersforTHIgroups(T1,T2)inrelationtoparityclasses(P1,P2,P3,P4,P5)andregions(East,Mediterranean,Central)

Parity

Parameter

Region/THIgroup

East Mediterranean Central

T1 T2 T1 T2 T1 T2

P1

Dailymilkyield,kg 17.734A 16.814B 17.264A 16.497A 15.809A 15.452B

Dailyfatcontent,% 4.110A 4.061B 4.246A 4.196B 4.279A 4.208B

Dailyproteincontent,% 3.445A 3.401B 3.452A 3.395B 3.447A 3.389B

P2

Dailymilkyield,kg 19.076A 18.038B 18.322A 17.842B 16.910A 16.605B



P3

Dailymilkyield,kg 19.173A 18.597B 18.564A 18.091A 17.187A 16.826B



P4




P5




*thevalueswithintheclassesofparityandregionsmarkedwiththedifferentlettersdifferhighlysignificant(P>0.01)


each0.55°Cincrease inrectaltemperature)whenmaximum THI reached 77. A significant negativecorrelationbetweenTHIandDMIwasdeterminedforcows in thesouth-easternU.S.(Holteretal.,1996;1997).SameauthorspresumethattheeffectofTHIisprobablymediatedthroughtheeffectsofincreasing body temperature on cowperformance.Umphrey et al. (2001) reported that the partialcorrelationbetweenmilkyieldandrectaltempera-tureforcowsinAlabamawas-0.135.Ravagnoloetal. (2000)determined thatmilk yield declined by0.2kgperunitincreaseinTHIwhenTHIexceeded72.Bouraouietal.(2002)observedthatthedailyTHI was negatively correlated to milk yield (r =-0.76) and feed intake (r= -0.24). Same authorsalsodetermined thatmilkyielddecreasedby0.41kgper cowper day for eachpoint increase in theTHI>69.Thereductioninmilkproductionduringheatstressmaybeduetodecreasednutrientintakeanddecreasednutrientuptakebytheportaldrainedvisceraofthecow.Bloodflowshiftedtoperipheraltissuesforcoolingpurposesmayalternutrientme-tabolismandcontributetolowermilkyieldduringhotweather.Westetal.(2002)reportedthat,dur-inghotweather,themeanTHItwodaysearlierhadthe greatest effect onmilk yield, while DMI wasmostsensitivetothemeanairtemperaturetwodaysearlier.MilkyieldforHolsteinsdeclined0.88kgperTHIunitincreaseforthe2-dlagofmeanTHI,whileDMIdeclined0.85kgforeachdegree(°C)increaseinthemeanairtemperature.Theauthorspresumethat the delayed impact of climatic variables onproductioncouldberelatedtoalteredfeedintake,delay between intake and utilization of consumednutrients,orchangesintheendocrinestatusofthecow.

Milk fat andmilkproteinpercentage alsode-creasesduetoheatstress.Bouraouietal.(2002)determineddecreaseofdailyfat(3.24vs.3.58%)andprotein(2.88vs.2.96%)content,aswellasde-creaseofdailyfat(0.68vs.0.48)andprotein(0.56vs.0.43)yieldsduring summer in regard to springperiod.Thedepressionsinmilkfatandproteinper-centages associated with heat stress environmentswere also determined by Rodrigez et al. (1985).Ontheotherhand,KnappandGrummer(1991)foundno significantdecrease in fatpercentage forcowsunderheatstress.Thedifferencebetweenre-sultsobtainedinthisresearchandthosereportedby

KnappandGrummer(1991)couldbecausedbyuse of totalmixed rations (TMR)which probablyalleviate milk fat depression commonly associatedwithheatstressbymaintainingtheintendedforageto concentrate intake and, ensuring adequate fibreforproperrumenfermentation. InthesamestudyKnapp andGrummer (1991) observeddecreaseof milk protein with increase of maximum dailytemperature.Thereductioninmilkproteinisprob-ablycausedbyadecreasedDMIandenergyintake.Emery(1978)quotedthatdecreasedlevelsoffoodintake during lactation are usually associated withdecreasedproteincontent.

Conclusions

BasedonanalysisofmicroclimaticconditionsinstablesinclimacticregionsofCroatiaandevaluationoftheeffectoftemperature-humidityindexvaluesonthedailyproductionofdairycattlefollowingcon-clusionscouldbeemphasised:

Thehighestmonthlyaveragesofambienttem-peratureduringanalysedperiodweredeterminedinMediterraneanregion,thehighestmonthlyaveragesofrelativehumidityduringanalysedperiodwereob-servedinCentralregion,whilethehighestmonthlymeanvaluesoftemperature-humidityindex(THI)weredeterminedinMediterraneanregion.

Heatstressconditionsindicatedwithmeandai-lyvaluesofTHI>72weredeterminedduringspringand summer season in all analysed regions. ThehighestincidenceofexceededTHIwasobservedinMediterraneanregion(15daysinspringand38daysin summer period). Absence of heat stress condi-tionsduringautumnandwinterseasoncharacterisedallthreeregions.

Highly significant (P<0.01) decrease of dailymilk yield due to enhanced THI was observed inallcowsregardless theparityclassand inall threeclimaticregions.RegardingtheeffectofTHIvalueabovecriticalondailyfatandproteincontent,high-lysignificant(P<0.01)decreasewasobservedinallcowsand inall analysed regions.Furthermore, themostdeteriorateeffectofheatstresswasobservedinEast region.Duringheat stressperiod,with theaimofminimizationoftheeffectsofheatstress,itisnecessarytoregulatemanagementstrategiesinthedairyherd.There aremany tools available tohelp


the dairy farmer combat heat stress. For instance,environmentalcoolingcanmaintainfeedintakeandnutrientdensityoffeedcanoptimizenutrientintaketomaintainmilkproduction.

Utjecaj vrijednosti temperaturno-humidnog indeksa

na dnevnu proizvodnju mliječnih goveda

Sažetak

Ciljevi su provedenoga istraživanja bili utvrdi-timikroklimatske uvjete u proizvodnim objektimau tri klimatske regije Hrvatske (istočna, medite-ranskatecentralna)teevaluiratiutjecajvrijednostitemperatutno-humidnog indeksa (THI) na dnevnuproizvodnjumliječnihgoveda.Utomjeciljuizbazepodataka HPA (Hrvatske poljoprivredne agencije)ekstrahirano1675686dnevnihzapisaprikupljenihurazdoblju od siječnja 2005. do travnja 2010. godi-ne.ZaprocjenuutjecajaTHInadnevnuproizvodnjumliječnihgovedakorištenjemodelfiksnihutjecajaukojemsuuvaženiutjecajistadijalaktacije,pasmine,sezone telenja, sezonemjerenja, teTHI grupe (T1-THI≤72;T2-THI>72).Modeljeapliciranzaseb-noporazredimaredoslijedalaktacije(P1,P2,P3,P4iP5)teregije.Tijekomanaliziranograzdoblja,najvišeprosječne mjesečne vrijednosti ambijentalne tem-peratureutvrđenesuumediteranskoj,najvišepro-sječnemjesečnevrijednostirelativnevlageutvrđenesuu centralnoj,dok sunajvišeprosječnemjesečnevrijednosti temperaturno-humidnog indeksa (THI)utvrđene u mediteranskoj regiji. Toplinsko stresniuvjeti indicirani prosječnom dnevnom vrijednošćuTHI>72utvrđeni su tijekomproljetne i ljetne se-zoneusvimanaliziranimregijama.Odsustvotoplin-skostresnihuvjetatijekomjesenskeizimskesezonekarakteriziralojesvetriregije.Visokosignifikantan(P<0.01) pad dnevne količinemlijeka te dnevnogsadržajamliječnemastiibjelančevinauzrokovanpo-višenomvrijednošćuTHIutvrđenjeusvihgrlane-ovisnooredoslijedu laktacije teusvimklimatskimregijama.Nadalje,najizraženijinegativniutjecaj to-plinskogstresautvrđenjeuistočnojregiji.Tijekomrazdoblja toplinskog stresa, s ciljemminimalizacijeutjecajaistog,neophodnajeprilagodbamanagemen-taustadumliječnihgrla.Uzgajivačimasunaraspola-ganjurazličitialatizaborbuprotivtoplinskogstresa.Naprimjer,hlađenjeokolišaomogućujeunosdostat-

nekoličinekrmivadokprikladansastavobrokaosi-guravadostatanunoshranjiva.Navedenoomogućavaodržavanjeoptimalneproizvodnjemlijeka.

Ključne riječi: mliječnagoveda;dnevnaproizvodnja;temperaturno-humidniindeks

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temperature-humidity index values and their significance

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