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

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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).

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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

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What Heat Stress?