Cooling Strategies During Heat StressPete Hansen, Serdal Dikmen, Miki Sakatani, and Geoff Dahl

Take Home Message #1

Cooling cows

When air temperature is high, the bestmethod to reduce heat stress is to:

1) reduce solar radiation

2) increase evaporative heat loss in conjunction with fans

Heat Loss

Heat Production

metabolites

Feed

Heat Gain

Heat Production + Heat Gain = Heat Loss

Radiation – heat transmitted by lightSunlight but also from other objects

Conduction – heat transmitted by physical contact between two stationery substances--still air--the ground--surface water

Convection – heat transmitted by physical contact of two substances moving past each otherwind

Evaporation – heat required to evaporate water

TYPES OF HEAT EXCHANGE

Heat is lost 22.4 times faster into water than air

It takes over 500 times as much heat to evaporate water as to raise its temperature by 1oF

Radiation

Conduction

Convection

Evaporation

TYPES OF HEAT EXCHANGE

Rate depends on difference betweenbody temperature and environment

Rate depends on humidity of the air

It is easier for cattle to regulate body temperature when: --heat production is not high (non-lactating vs lactating)--air temperature is lower than body temperature (101.3oF)--solar radiation is not high--loss of radiation to night sky is high (no roof or clouds)--humidity is not high

Air temperature = 85oF Relative humidity=50% Cow is under shade

evaporationby respiration

evaporationby sweating

conductionconvection

radiation

101.3oF

Heat Production = Net Heat LossBody temperature remains normal

evaporationby respiration

reduced

evaporationby sweating

reduced

conduction &convection reduced

radiation gain from sun

Air temperature = 94oF Relative humidity=90% Cow is not under shade

102.4oF

Heat Production > Net Heat LossBody temperature rises

101..7oF

Reduce radiant heat load

Increase evaporative heat loss

Increase conduction& convection

Increase evaporationand convection

102.4oF

Take Home Message #2

Evaporative cooling

Not clear whether sprinklers or foggers workbest

probably sprinklers, esp. when humidity is high

Tunnel ventilation doesn’t necessarily work better than freestall barns

Cross ventilation may be very effective high investment costs

Designed to wet the cow

Increase loss of heat --conduction-convection--evaporation

Designed to cool the air by evaporation --increased conduction and convection

Some water reaches cow but the small drop size limits water that penetrates hair coat

Farm 4Barn 1

Farm 1 Farm 2 Farm 3 Farm 4Barn 2

Farm 4Barn 3

Farm 5Barn 1

Farm 5Barn 2

Farm 5Barn 3

Farm 5Barn 4

Freestalls with fans and sprinklers Tunnel ventilation

100.4

101.3

102.2

103.1

Rec

tal t

empe

ratu

re (

o F)

Average afternoon rectal temperatures of cowsin Florida during the summer

Take Home Message #3

Which Animals Should be Cooled

Don’t forget the dry cows

Cool calves and growing heifers too

Effect of cooling dry cows with fans and sprinklers from 46 days before expected calving

on subsequent milk yield (Florida)

Do Amaral et al., J Dairy Sci. 92:5988-5999 (2009)

cooled

Not cooled

16.5 lb diff

Body temperature – Wisconsin (Sartori et al., 2002)

Infertility

101.1

101.5

101.8

102.2

102.9

103.3

103.6

104.0

102.6

Hour of the day

8 10 12 14 16 18

Vag

inal

tem

per

atu

re (

oF

)

100

101

102

103

104

105

Vaginal temperatures in two non-lactating cows during one summer day

Infertility

Shade cloth

Foggers and fans

Rectal temperature Maximum THI ADG (lb/d)

April 4-June 11 65.2 1.0 + 0.04

June 12 – Sept 14 74.8 0.9 + 0.04*

Sept 15-Nov 24 59.7 1.1 + 0.04

Growth rate from birth to weaning of dairy calves reared in hutches as affected by month of birth

(Slovak Republic)

*P<0.05

Broucek et al., Int J Biometeorol. 59:201 (2009)

Take Home Message #4

Assessing the degree of heat stress

Measure body temperatures!!!

Measure differences in performance between summer and winter

Body Temperatures at Which CowsExperience Declines in Production

And Reproduction

Milk yields and conception rates decline at afternoonrectal temperatures > 102.2oF

The critical vaginal temperatures are ~ 102.2 to 102.5oF in the PM

1 inch

CIDR

iButtonDS1921H-F5#Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 High-Resolution Thermochron® iButton® model DS1921H, Range H: +15°C to +46°C

Hour of the Day

0 400 800 1200 1600 2000 2400

Vag

inal

tem

per

atu

re (

o C)

38.2

38.4

38.6

38.8

39.0

39.2

39.4

milking

Irrigation pivot

Average vaginal temperatures for lactating Holsteins on a grazing dairy in Florida during the summer

Infertility

Vaginal temperatures are about 0.2-0.4oF higher than rectal temperatures

100.8

101.1

101.5

101.8

102.2

102.6

Tem

pera

ture

, o F

  Conception rate (%)

High production Low production

Intensive cooling

Moderate cooling

Intensive cooling

Moderate cooling

Winter 39 39 40 39

Summer 19 12 25 3

         

Summer:winter ratio

0.49 0.31 0.62 0.08

Summer to winter ratios for conception rate in Israeli herds as affected by production level and intensity of

cooling (Flamenbaum and Galon, 2010)

Intensive – wetting/fans 10X/d Moderate wetting/fans 3X/d Values for milk yield are 0.96-1.03 for intensive cooling and 0.84-0.90 for moderate cooling

Take Home Messages

Cool cows by providing good shade anda combination of evaporative cooling and fans More water the better if available and waste

not a problem Tunnel ventilation may not be best Cross ventilation may be worthwhile

Don’t just cool lactating cowsheifers and dry cows as well

Measure how effective cooling is Body temperatures Summer: winter ratios

Supported by Agriculture and Food Research Initiative Competitive Grant no. 2010-85122-20623 from the USDA National Institute of Food and Agriculture