Robert E' Graves

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Robert E. Graves Agricultural and Biological
Engineering Penn State University
HEAT STRESS
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Heat Gain
Heat Stress
Heat gain is higher than heat loss

• Body Heat metabolism, physical activity,
  performance
• Environment radiation (sun), convection (air),
  conduction (resting surface)

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Effects of heat stress

• Respiration rate increases
• Sweating increases
• Water intake increases
• Dry matter intake decreases
• Feed passage rat decreases
• Blood flow to internal organs decreases
• Milk production decreases
• Reproductive performance decreases

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Smith et al
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The Cow and Heat Stress

• Not a hot weather animal.
• Likes things cooler than we do.

Cow Numbers
ShearerBeede

• Thermal Comfort Zone 41 77F (5 25C)
• Lower critical temperature (feel cold/increase
  body heat production)
• Neonatal calves 55F (13C)
• Mature, peak lactation cows 13F (-25C)
• Upper critical temperature 77-78F (25C)

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Lower Critical Temperature
Upper Critical Temperature
Intake
Gain
Thermal Comfort Zone
Kilocalories
Maintenance
Cold
Heat
Effective Temperature
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More Cow Numbers

• Body Temperature 101.5F
• Sweating begins
• European 90F (32C)
• Zebu 95F (35C)
• Panting begins 1-2 degrees higher than sweating

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ShearerBeede
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Heat Transfer

• Radiation (line of sight)
• Convection (air movement)
• Conduction (direct contact)
• Evaporation (phase change)

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Dairy Cow Sensible Heat Flows
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Direct Radiation

• Indirect
• Radiation

Convection to surrounding air
Indirect Radiation
Air Velocity Increased Convection
Conduction To/From Surface
Digestive Heat
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Latent Heat Flow

• Evaporation From Skin

Respiratory Tract - moisture in respired air
(slight temp increase)
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100
75
Nonevaporative Cooling
Heat Dissipation,
50
Evaporative Cooling Outer Body Surface
25
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Evaporative Cooling Respiratory Tract
0
0
20
40
60
80
ShearerBeede
Chamber Temperature, ºF
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Nutrition
Water

• 3.5 45 gallons per day
• Increase 1.2 2 X

Smith et al

• Maintenance requirements increase
• Feed intake decreases
• 2/3 intake evening
• Increase MC of TMR
• Increase energy density

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Smith et al
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Routes of Body Water Loss (Lb/day) Nonlactating
Cows During Heat Stress
68ºF 86ºF Difference in Hot
Environments Feces 28.6 21.6 -24.6 Urine
25.7 32.3 25.6 Saliva 0.0 5.3
N/A Respiratory 16.8 25.7 53.9 Body
surface 23.3 64.5 176.4 Total 94.9 149.4
58.3
ShearerBeede
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Relative Humidity,
80
100
40
60
0
20
72
NO STRESS
80
MILD STRESS
90
HEAT STRESS
Degrees, F
SEVERE STRESS
100
110
DEAD COWS
120
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Results
Feed and water are diverted to deal with heat
(panting, sweating) DMI decreases due to
heat Milk production down Repro down Health
problems up
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Signs of Heat Stress

• Rectal temps above 102.5F
• Respiration rates greater than 80 breaths per
  minute
• Dry matter intake and milk production drop

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Actions
S A A W H I I A A
R R T D
E E E V R X
E C L H
O A C N
I G T E Y
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Shade

• Lowers solar heat load

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Air Exchange

• Removes hot, moist air from the animal
  environment
• Increases convective heat loss
• 1000 cfm per animal recommended

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Air Velocity

• Increases cows cooling ability by moving air
  close to skin
• Must create turbulence around co
• 220 to 440 fpm (2.5 to 5 mph)

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Water

• Water intake greatly increased
• More watering locations
• Sprinkling wet cows hide, direct evaporative
  cooling
• Misting/Evap Pads cool air that cools cow

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Conclusion

• Heat stress affects
• DMI, production, repro
• Heat stress means more gain than loss
• Solution
• Shade, air, water

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Resources

• March 2002 Dairy Digest
• Tunnel Ventilated for Dairy Tie Stall Barns -
  ABE Fact Sheet G 78
• http//search.oznet.ksu.edu81/query.html?qt2000
  HeartofAmerica

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