Heat Stress in Dairy Cattle

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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 thermo neutral
  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 (or other animal)
  cannot dissipate an adequate quantity of heat to
  maintain body thermal balance or normal body
  temperature

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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 gt 72 is considered to indicate heat stress
  in dairy cattle

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Example of the Interaction of Temperature and
Humidity in Determining Heat Stress Potential in
Dairy Cattle
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All of These THI of 72
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How Do Cows Respond to Heat Stress?

• Higher body temperatures
• Increased respiration rates (gt70/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 commercial
  herds - 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 productive
  functions - Lower dry matter intake -
  Alterations in nutrient use - Can drop 10 to gt
  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 matter Intake and Milk Production

• Used the CNCPS ration model to predict 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
1 lb. of fat was added to the ration in Run 5
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Maintenance Energy Required Mcal
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Predicted Dry Matter Intake, lbs.
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Predicted Milk Production, lbs.
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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,
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Heat Stress Loss Estimates by State, Millions of
Dollars
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What Can We Do to Minimize 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 heat production during
  digestion)
• Consider added fat - Concentrated energy
  source - Low heat of digestion

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Ration Adjustments - 2

• Replace some forage with non-fiber byproduct
  feeds (beet pulp, soy hulls)
• Minimize excess total and rumen degradable
  protein (requires energy to excrete from the
  body)
• Consider buffers, yeast and added minerals

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Feeding Management Changes

• Fresh, palatable high quality feed should always
  be available
• Uniformity of mixed and delivered rations
• Minimize feed sorting
• Shift feeding times to cooler part of the day

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Water

• Intake may increase by 20 to gt50 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 to refill 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 installed to wet the
  cows skin?

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What Heat Stress?
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THI Thresholds for Other Species

• Beef cattle 72 75 o F
• Swine 72 74 o F
• Poultry 70 78 o F

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Summary

• Heat stress can decrease animal production,
  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 investment cost
  versus projected returns
• In the Northeast, we have a low number of heat
  stress days
• New facilities being built are incorporating
  housing components to minimize the effect of heat
  stress

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What Heat Stress?
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