7.Cattle Chase

8/12/2019 7.Cattle Chase

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Heat Stress in Dairy

Cattle Dr. L. E. Chase

Dept. of Animal

Science Cornell University


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Introduction

All animals have a zone of thermoneutral temperatures conducive to

normal function The upper critical temperature is

where the effects of heat stress start

to appear


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Heat Stress

The point at which a dairy cow (orother animal) cannot dissipate an

adequate quantity of heat to maintainbody thermal balance or normal bodytemperature


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Source: NRC, 1981


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Temperature Humidity

Index (THI) Includes both temperature and

humidity in determining the point sat

which heat stress may occur

A THI > 72 is considered to indicate

heat stress in dairy cattle


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Example of the

Interaction ofTemperature and

Humidity inDetermining Heat

Stress Potential inDairy Cattle


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All of These = THI of 72

Temperature, o F Humidity, %

84 15

80 30

77 50

75 65

72 95


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How Do Cows Respond to

Heat Stress? Higher body temperatures

Increased respiration rates (>70/hour)

Less activity

Increased water intake

Seek shade Look for cool areas in the barn


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What Happens

Metabolically? Energy requirements for maintenance

increase

- Increased respiration rate-More blood flow to the skin- Less blood flow to body core

- May increase by 20-30%


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What About Dry Matter

Intake? Dry matter intake decreases in cows

subjected to heat stress

- May drop 10-20% in commercialherds

- Becomes variable

- May be short or long-term


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How About Milk

Production? Decreases due to:

- More energy for maintenance

- Less energy for productivefunctions

- Lower dry matter intake

- Alterations in nutrient use- Can drop 10 to > 25%


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What Happens to

Reproduction? Usually decreases in heat stress

situations

Estrus intensity and length decrease

Fertility rate decreases

Ovarian follicle growth decreases

Increase early embryonic death

May affect fetal growth


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What Determines the

Severity of Heat Stress?Actual temperature and humidity

Length of the heat stress period

Degree of cooling that occurs at night

Ventilation and air flow

Cow factors (size, milk production) Water availability

Hair coat depth


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Which Cow Will Be Affected

More by the Sun?


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Heat Stress, Dry matterIntake and Milk Production

Used the CNCPS ration model topredict dry matter intake and milk

production Cow = 1,400 lbs producing 80 lbs. of

milk

Varied temperature and humidity


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Conditions for Each Run

Run Temp., F Humidity NightTemp.

1 60 50 50

2 90 50 60

3 90 70 60

4 90 70 75

5 90 70 75

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


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Maintenance Energy

Required

Mcal

02

468

10

1214

1618

20

ME, Mcal

1 2 3 4 5

Run


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Predicted Dry Matter

Intake, lbs.

20

25

30

35

40

45

50

DMI, lbs.

1 2 3 4 5

Run


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Predicted Milk

Production, lbs.

010

20

30

40

5060

70

80

90

Milk, lbs.

1 2 3 4 5

Run

ME

MP


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Economic Impact of Heat

Stress St-Pierre et. al., 2003

Estimated costs of heat stress for both

the US and each state

Included dairy cattle, beef cattle,swine and poultry

Yearly cost = $2.4 billion dollars


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Total Loss by Animal

Type, %

Dairy

Beef

Swine

Poultry


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Heat Stress Loss Estimatesby State, Millions of Dollars

State Loss, Million $ Dairy, % ofTotal Loss

New York 24.9 98

Pennsylvania 50.8 88

Vermont 5.4 98

Maryland 8.75 86


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What Can We Do toMinimize the Effects of Heat

Stress? 2 basic approaches -

a. Adjust the ration

b. Adjust the environment in

which the cow lives


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Ration Adjustments

Need to keep the animal healthy!!!

Select higher quality forages and more

digestible feed ingredients (lower heatproduction during digestion)

Consider added fat

- Concentrated energy source- Low heat of digestion


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Ration Adjustments - 2

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

Minimize excess total and rumendegradable protein (requires energy toexcrete from the body)

Consider buffers, yeast and addedminerals


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Feeding Management

Changes Fresh, palatable high quality feed

should always be available

Uniformity of mixed and deliveredrations

Minimize feed sorting

Shift feeding times to cooler part ofthe day


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Water

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

Clean, fresh water always available

Adequate watering devices or space(minimum of 2-3 inches per cow)

Make sure pressure is adequate torefill waterers


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Housing and Facility

Adjustments Minimize overcrowding

Minimize time in the holding area

Is shade available?

Can air flow be increased with fans?

Can misters or sprinklers be installedto wet the cows skin?

Wh t H t St ?


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What Heat Stress?


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THI Thresholds for Other

Species Beef cattle = 7275 o F

Swine = 7274 oF

Poultry = 7078 oF


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Summary

Heat stress can decrease animalproduction, reproduction and

profitability Ration, feeding management and

housing alterations can be made to

lower the effect of heat stress


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Summary - 2

The challenge is to balance investmentcost versus projected returns

In the Northeast, we have a lownumber of heat stress days

New facilities being built are

incorporating housing components tominimize the effect of heat stress


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What Heat Stress?


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