Heat Stress and the Dairy Industry Lance Baumgard AnSc 435
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Heat Stress and the Dairy Industry
Lance Baumgard
AnSc 435
When environmental temperature nears the cow’s body temperature ( > 90 deg F), the cow’s cooling mechanisms are impaired
Consequently the cow’s body temperature rises and the cow shows signs of heat stress.
The first sign … eats less to produce less metabolic heat … a natural protective mechanism.
Temperature Humidity Index(THI)
Easy way to measure andevaluate heat stress
All of These = THI of 72
Temperature, o F Humidity, %
84 15
80 30
77 50
75 65
72 95
Heat Stress is a Global Problem
January 2003, NASA
July 2003, NASA
40% of W. Canadian summer days THI > 72Ominski et al., 2002
Decrease in production (milk and growth)
Reduced body condition
Acute and chronic health problems
Decreased reproductive indices
Abortions
Animal death
Possibly the most costlyissue affecting global animal agriculture
Ruminants & Heat Stress
rumen acidosis & laminitis
Annual loss to American Dairy Industry is: $897 million to $1.5 billion
Annual Loss to American Beef Industry is > $350 MillionSt-Pierre et al., 2003 J. Dairy Sci. E52-E77
June 2006 California Heat Wave: $1 BillionCDFA, 2006
>2,000 cattle died in NebraskaJune 2009
Economic Impact of Heat StressEconomic Impact of Heat Stressto US Animal Agricultureto US Animal Agriculture
• St-Pierre et. al., 2003
• dairy cattle, beef cattle, swine and poultry
• Yearly cost = $2.4 billion dollars
Total Loss by Animal Type, %
DairyBeefSw inePoult ry
1995
1999
2005
2006
2006
Iowa and Heat Stress
• Estimated Iowa Impact (St-Pierre et al., 2003)• Assumes optimum heat abatement
– Dairy $23.9 million– Beef and Swine $45.5 million– Poultry $4.3 million
Total Iowa impact $73.7 million
www.dairyaustralia.com.au
Bare ground surface temperature before and after shading at various times during the daya
Shaded time Temperature of Ground Surface (°F) (min) 11 a.m. 12 noon 2 p.m. 4 p.m. In sun 124.9 144.3 151.9 153.0 5 104.0 107.6 111.6 113.7 15 98.1 103.1 109.4 109.4 30 98.1 101.3 104.0 105.8 Air temp 91.9 95.0 98.1 104.0 aFrom Kelly et al. (1950).
www.dairyaustralia.com.au
www.dairyaustralia.com.au
www.dairyaustralia.com.au
www.dairyaustralia.com.au
Inactive person, 180 lbs generates about as much heat as a 100-watt light bulb …
… A 1,600 lb Holstein is equivalent to about nine 100-watt light bulbs
For milk cows, add one 100-watt light bulb for every 10 lbs of milk produced a day…
… The 1,600 lb Holstein producing 80 lbs per day is producing heat equivalent to (17) 100-watt light bulbs!
Add solar radiation in hot climates and we now have a “33-bulb” cow!
Heat Stressed Cows
Decrease in milk production
Reduced body condition
Acute health problems
Significant drop in pregnancy rate
High incidence of abortions
High death loss Added all up … costly!
Results of Heat Stress
Rumen acidosis
Rumen Acidosis: Reduced cellulose digestion Laminitis Milk fat depression etc…
Effect of Heat Stress on Ruminal pH of
Holstein Cows (Mishra et al., JAS 30:1023)
5
5.3
5.6
5.9
6.2
6.5
6.8
High Forage Diet High Concentrate Diet
COOL
COOL
HOT H
OT
Ru
min
al p
H
Effect of Heat Stress on Digestive Physiology
DMI
Less Total Saliva
Slobbering
Less Saliva to Rumen
Less Salivary Buffer to Rumen
Heat Stress
Rumen pH
De Rensis and Scaramuzzi, 2003
Florida South Africa
Arizona
Minnesota
Dairy Study #1
• Multiparous Holstein cows (n=23; 120 ± 30 DIM)• Environmental Conditions
1) Thermal neutral conditions (constant 18ºC & 20% humidity) for 1 week
2) Heat stress (cyclical temps 29.4 to 37.8ºC & 20% humidity) for 3 weeks
• Heat stress variables– Body temperature: 40.5ºC at 1400 h– Respiration rates: 40 to 82 breaths/min
Feed Intake
10
12
14
16
18
20
22
1 2 3 4
Week
DM
I, k
g/d
Thermal Neutral Cyclical Heat Stress
a
b
c
d
Shwartz et al., 2009
Milk Yield
10
15
20
25
30
35
40
1 2 3 4
Week
kg/d
Thermal Neutral Cyclical Heat Stress
a
b
c c
Shwartz et al., 2009
Energy Balance
-5
-4
-3
-2
-1
0
1
2
3
4
5
Mc
al/d
/d
Thermal Neutral Cyclical Heat Stress
a
b
c
d
1 2 3 4
Week
Shwartz et al., 2009
Maintenance cost ↑ 25%: 1989 NRC
Heat Stress and NEFA
0
100
200
300
400
500
1 2 3 4
Week
uE
q/l
Thermal Neutral Cyclical Heat Stress
Shwartz et al., 2009
Interesting Observations
– Feed intake acclimated to heat stress but milk yield did not
• Suggests something in addition to reduced feed intake is decreasing milk yield during heat stress
– Despite the negative energy balance and loss of body weight adipose tissue was not mobilized
Heat Stress Questions??
Does the decrease in feed intake explain the reduced milk yield during heat stress?
Indirect vs. direct effects of heat
If we have a better understanding of the biological reasons WHY heat stress reduces production, we’ll have a better idea of how to alleviate it.
Lactation Trials
• Multiparous Holstein cows (~120 DIM)• Environmental conditions:
1) Period 1: thermal neutral conditions (constant 18ºC & 20% humidity) for ~10 days
2) Period 2: heat stress (cyclical temps 29.4 to 40ºC & 20% humidity) for ~10 days or pair-fed* a thermal neutral group to keep nutrient intake similar
Rhoads et al., 2009Wheelock et al., 2008Wheelock et al., 2009
* Pair feeding eliminates confounding effects of dissimilar feed intake
10
12
14
16
18
20
1 2 3 4 5 6 7 8 9
Day
DM
I (k
g/d
)
Heat Stress
Underfed
Effects of Heat Stress on Feed Intake
Rhoads et al., 2009
Heat stress ↓ feed intake by ~30 %
Heat stress
Pair-fed
20
25
30
35
40
45
50
0 1 2 3 4 5 6 7 8 9
Day
Mil
k Y
ield
(kg
/d)
Heat-stressed
Pair-fed
Effects of Environment on Milk Yield
Rhoads et al., 2009Wheelock et al., 2008Wheelock et al., 2009Baumgard and Rhoads, unpublished
Heat stress ↓ yield ~45%Pair-feeding ↓ yield by ~19%
Thus, ↓ feed intake only accounts for ~50% of the reductions in milk yield
Calculated Energy Balance
-8
-6
-4
-2
0
2
4
6
-1 1 2 3 4 5 6 7 8 9
Day
Mca
l/d
PF
HS
Maintenance cost ↑ 25%: 1989 NRC
Body Weight LossFrom Period 1 to 2
-60
-50
-40
-30
-20
-10
0
kg
Heat StressPair-fed
0
100
200
300
400
500
600
1 2 3 4 5 6 7 8 9
Day
NE
FA
(u
Eq
/l)
Heat-stressed
Pair-fed
Effects of Heat Stress on Adipose Tissue Mobilization
Rhoads et al., 2009
-0.1
0.1
0.3
0.5
0.7
0.9
1.1
1.3
1.5
1 2 3
Period
Insu
lin (
ng
/ml)
Heat Stressed
Pair-fed
Circulating Insulin in Lactating Dairy Cows
Wheelock et al., 2006
Where to cool cows?
• Free stalls or dry lot pens
• Holding pen
• Maternity pen
• Parlor exit lane
• Feed lines/feed alleys
• Feed bunks
Feed Alley Cooling
www.dairyaustralia.com.au
What Heat Stress?
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