7.cattle chase
TRANSCRIPT
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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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