cooling strategies during heat stress- hansen
TRANSCRIPT
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