Heat Stress in Dairy Heat Stress in Dairy CattleCattle

Akrum HamdyAkrum Hamdy

IntroductionIntroduction

All animals have a zone of thermo All animals have a zone of thermo neutral temperatures conducive neutral temperatures conducive to normal functionto normal function

The upper critical temperature is The upper critical temperature is where the effects of heat stress where the effects of heat stress start to appearstart to appear

Heat StressHeat Stress

The point at which a dairy cow (or The point at which a dairy cow (or other animal) cannot dissipate an other animal) cannot dissipate an adequate quantity of heat to adequate quantity of heat to maintain body thermal balance maintain body thermal balance or normal body temperatureor normal body temperature

Source: NRC,

1981

Temperature Humidity Temperature Humidity Index (THI)Index (THI) Includes both temperature and Includes both temperature and

humidity in determining the point humidity in determining the point sat which heat stress may occursat which heat stress may occur

A THI > 72 is considered to A THI > 72 is considered to indicate heat stress in dairy cattleindicate heat stress in dairy cattle

Example of the Interaction of

Temperature and Humidity in Determining Heat Stress

Potential in Dairy Cattle

All of These = THI of All of These = THI of 7272

Temperature, Temperature, o o FF Humidity, %Humidity, %

8484 1515

8080 3030

7777 5050

7575 6565

7272 9595

How Do Cows Respond How Do Cows Respond to Heat Stress?to Heat Stress? Higher body temperaturesHigher body temperatures Increased respiration rates Increased respiration rates

(>70/hour)(>70/hour) Less activityLess activity Increased water intakeIncreased water intake Seek shadeSeek shade Look for cool areas in the barnLook for cool areas in the barn

What Happens What Happens Metabolically?Metabolically? Energy requirements for Energy requirements for

maintenance increase maintenance increase - Increased - Increased

respiration raterespiration rate -More -More blood flow to the skinblood flow to the skin - - Less blood flow to body coreLess blood flow to body core

- May increase by 20-- May increase by 20-30%30%

What About Dry Matter What About Dry Matter Intake?Intake? Dry matter intake decreases in Dry matter intake decreases in

cows subjected to heat stresscows subjected to heat stress- May drop 10-20% - May drop 10-20%

in commercial herdsin commercial herds- Becomes - Becomes

variablevariable - May - May be short or long-termbe short or long-term

How About Milk How About Milk Production?Production? Decreases due to:Decreases due to:

- More energy for - More energy for maintenancemaintenance - Less energy for - Less energy for productive functionsproductive functions

- Lower dry matter - Lower dry matter intakeintake - Alterations in - Alterations in nutrient usenutrient use - Can drop - Can drop 10 to > 25%10 to > 25%

What Happens to What Happens to Reproduction?Reproduction? Usually decreases in heat stress Usually decreases in heat stress

situationssituations Estrus intensity and length Estrus intensity and length

decreasedecrease Fertility rate decreasesFertility rate decreases Ovarian follicle growth decreasesOvarian follicle growth decreases Increase early embryonic deathIncrease early embryonic death May affect fetal growthMay affect fetal growth

What Determines the What Determines the Severity of Heat Severity of Heat Stress?Stress? Actual temperature and humidityActual temperature and humidity Length of the heat stress periodLength of the heat stress period Degree of cooling that occurs at Degree of cooling that occurs at

nightnight Ventilation and air flowVentilation and air flow Cow factors (size, milk production)Cow factors (size, milk production) Water availabilityWater availability Hair coat depthHair coat depth

Which Cow Will Be Which Cow Will Be Affected More by the Affected More by the Sun?Sun?

Heat Stress, Dry matter Heat Stress, Dry matter Intake and Milk Intake and Milk ProductionProduction Used the CNCPS ration model to Used the CNCPS ration model to

predict dry matter intake and milk predict dry matter intake and milk productionproduction

Cow = 1,400 lbs producing 80 lbs. Cow = 1,400 lbs producing 80 lbs. of milkof milk

Varied temperature and humidityVaried temperature and humidity

Conditions for Each Conditions for Each RunRun

RunRun Temp., FTemp., F HumidityHumidity Night Night Temp.Temp.

11 6060 5050 5050

22 9090 5050 6060

33 9090 7070 6060

44 9090 7070 7575

55 9090 7070 7575

1 lb. of fat was added to the ration in Run 5

Maintenance Energy Maintenance Energy Required – McalRequired – Mcal

02468

101214161820

ME, Mcal

1 2 3 4 5

Run

Predicted Dry Matter Predicted Dry Matter Intake, lbs.Intake, lbs.

20

25

30

35

40

45

50

DMI, lbs.

1 2 3 4 5

Run

Predicted Milk Predicted Milk Production, lbs.Production, lbs.

0102030405060708090

Milk, lbs.

1 2 3 4 5

Run

MEMP

Economic Impact of Economic Impact of Heat StressHeat Stress St-Pierre et. al., 2003St-Pierre et. al., 2003 Estimated costs of heat stress for Estimated costs of heat stress for

both the US and each stateboth the US and each state Included dairy cattle, beef cattle, Included dairy cattle, beef cattle,

swine and poultryswine and poultry Yearly cost = $2.4 billion dollarsYearly cost = $2.4 billion dollars

Total Loss by Animal Total Loss by Animal Type, %Type, %

DairyBeefSwinePoultry

Heat Stress Loss Heat Stress Loss Estimates by State, Estimates by State, Millions of DollarsMillions of Dollars

StateState Loss, Million Loss, Million $$

Dairy, % of Dairy, % of Total LossTotal Loss

New YorkNew York 24.924.9 9898

PennsylvaniPennsylvaniaa

50.850.8 8888

VermontVermont 5.45.4 9898

MarylandMaryland 8.758.75 8686

What Can We Do to What Can We Do to Minimize the Effects of Minimize the Effects of Heat Stress?Heat Stress? 2 basic approaches -2 basic approaches -

a. Adjust the rationa. Adjust the ration

b. b. Adjust the environment inAdjust the environment in

which the cow lives which the cow lives

Ration AdjustmentsRation Adjustments

Need to keep the animal healthy!!!Need to keep the animal healthy!!! Select higher quality forages and more Select higher quality forages and more

digestible feed ingredients (lower heat digestible feed ingredients (lower heat production during digestion)production during digestion)

Consider added fatConsider added fat- Concentrated energy source- Concentrated energy source

- Low heat of digestion- Low heat of digestion

Ration Adjustments - 2Ration Adjustments - 2

Replace some forage with non-Replace some forage with non-fiber byproduct feeds (beet pulp, fiber byproduct feeds (beet pulp, soy hulls)soy hulls)

Minimize excess total and rumen Minimize excess total and rumen degradable protein (requires degradable protein (requires energy to excrete from the body)energy to excrete from the body)

Consider buffers, yeast and added Consider buffers, yeast and added mineralsminerals

Feeding Management Feeding Management ChangesChanges Fresh, palatable high quality feed Fresh, palatable high quality feed

should always be availableshould always be available Uniformity of mixed and delivered Uniformity of mixed and delivered

rationsrations Minimize feed sortingMinimize feed sorting Shift feeding times to cooler part Shift feeding times to cooler part

of the dayof the day

WaterWater

Intake may increase by 20 to >50% Intake may increase by 20 to >50% during heat stressduring heat stress

Clean, fresh water always availableClean, fresh water always available Adequate watering devices or space Adequate watering devices or space

(minimum of 2-3 inches per cow)(minimum of 2-3 inches per cow) Make sure pressure is adequate to Make sure pressure is adequate to

refill waterersrefill waterers

Housing and Facility Housing and Facility AdjustmentsAdjustments Minimize overcrowdingMinimize overcrowding Minimize time in the holding areaMinimize time in the holding area Is shade available?Is shade available? Can air flow be increased with Can air flow be increased with

fans?fans? Can misters or sprinklers be Can misters or sprinklers be

installed to wet the cow’s skin?installed to wet the cow’s skin?

What Heat Stress?

THI Thresholds for THI Thresholds for Other SpeciesOther Species Beef cattle Beef cattle = 72 – 75 = 72 – 75 o o FF

SwineSwine = 72 – 74 = 72 – 74 oo F F

PoultryPoultry = 70 – 78 = 70 – 78 oo F F

SummarySummary

Heat stress can decrease animal Heat stress can decrease animal production, reproduction and production, reproduction and profitabilityprofitability

Ration, feeding management and Ration, feeding management and housing alterations can be made housing alterations can be made to lower the effect of heat stressto lower the effect of heat stress

Summary - 2Summary - 2

The challenge is to balance The challenge is to balance investment cost versus projected investment cost versus projected returnsreturns

In the Northeast, we have a low In the Northeast, we have a low number of heat stress daysnumber of heat stress days

New facilities being built are New facilities being built are incorporating housing components incorporating housing components to minimize the effect of heat stressto minimize the effect of heat stress

What Heat Stress?What Heat Stress?

Monsanto