Cooling Strategies During Heat Stress- Hansen


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Cooling Strategies During Heat Stress- Hansen

  1. 1. Cooling Strategies During Heat StressPete Hansen, Serdal Dikmen, Miki Sakatani, and Geoff Dahl
  2. 2. Take Home Message #1 Cooling cowsWhen 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
  3. 3. Heat GainHeat Loss Heat Production metabolites Feed Heat Production + Heat Gain = Heat Loss
  4. 4. TYPES OF HEAT EXCHANGERadiation – heat transmitted by lightSunlight but also from other objectsConduction – heat transmitted by physical contact betweentwo stationery substances--still air--the ground Heat is lost 22.4 times faster into water than air--surface waterConvection – heat transmitted by physical contact of twosubstances moving past each otherwindEvaporation – heat required to evaporate water It takes over 500 times as much heat to evaporate water as to raise its temperature by 1oF
  5. 5. TYPES OF HEAT EXCHANGERadiation Rate depends on difference betweenConduction body temperature and environmentConvectionEvaporation 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
  6. 6. Air temperature = 85oF Relative humidity=50% Cow is under shadeevaporation conduction radiationby sweating convection 101.3oF Heat Production = Net Heat Loss Body temperature remains normal evaporation by respiration
  7. 7. Air temperature = 94oF Relative humidity=90% Cow is not under shade conduction & radiation convection reduced evaporation gain from sun by sweating reduced 102.4oF evaporation by respiration reducedHeat Production > Net Heat LossBody temperature rises
  8. 8. Increase evaporation and convection Increase conduction Reduce radiant heat load & convectionIncrease evaporative heat loss 102.4oF 101..7oF
  9. 9. Take Home Message #2 Evaporative coolingNot clear whether sprinklers or foggers workbest probably sprinklers, esp. when humidity is highTunnel ventilation doesn’t necessarily workbetter than freestall barnsCross ventilation may be very effective high investment costs
  10. 10. Designed to wetthe cowIncrease loss of heat--conduction-convection--evaporation
  11. 11. Designed to cool the air by evaporation--increased conduction and convectionSome water reaches cow but the small drop size limitswater that penetrates hair coat
  12. 12. Average afternoon rectal temperatures of cows in Florida during the summerRectal temperature (oF) 103.1 102.2 101.3 100.4 Farm 1 Farm 2 Farm 3 Farm 4 Farm 4 Farm 4 Farm 5 Farm 5 Farm 5 Farm 5 Barn 1 Barn 2 Barn 3 Barn 1 Barn 2 Barn 3 Barn 4 Freestalls with fans and sprinklers Tunnel ventilation
  13. 13. Take Home Message #3 Which Animals Should be CooledDon’t forget the dry cowsCool calves and growing heifers too
  14. 14. Effect of cooling dry cows with fans and sprinklers from 46 days before expected calving on subsequent milk yield (Florida) cooled 16.5 lb diff Not cooled Do Amaral et al., J Dairy Sci. 92:5988-5999 (2009)
  15. 15. Body temperature – Wisconsin (Sartori et al., 2002)104.0103.6103.3102.9102.6102.2 Infertility101.8101.5101.1
  16. 16. Vaginal temperatures in two non-lactating cows during one summer day 105Vaginal temperature ( F) Shade clotho 104 103 Infertility 102 Foggers and fans 101 100 8 10 12 14 16 18 Hour of the day
  17. 17. Growth rate from birth to weaning of dairy calves reared in hutches as affected by month of birth (Slovak Republic)Rectal temperature Maximum THI ADG (lb/d) April 4-June 11 65.2 1.0 + 0.04June 12 – Sept 14 74.8 0.9 + 0.04* Sept 15-Nov 24 59.7 1.1 + 0.04 *P<0.05 Broucek et al., Int J Biometeorol. 59:201 (2009)
  18. 18. Take Home Message #4 Assessing the degree of heat stressMeasure body temperatures!!!Measure differences in performance betweensummer and winter
  19. 19. Body Temperatures at Which Cows Experience Declines in Production And ReproductionMilk yields and conception rates decline at afternoonrectal temperatures > 102.2oFThe critical vaginal temperatures are ~ 102.2 to 102.5oFin the PM
  20. 20. DS1921H-F5#iButton Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 High-Resolution Thermochron® iButton® model DS1921H, Range H: +15°C to +46°C CIDR 1 inch
  21. 21. Average vaginal temperatures for lactating Holsteins on a grazing dairy in Florida during the summer 102.6 39.4 Infertility Temperature,(oC) oF 39.2 102.2 Vaginal temperature 39.0 101.8 38.8 101.5 101.1 38.6 Irrigation pivot 100.8 38.4 milking 38.2 0 400 800 1200 1600 2000 2400 Hour of the DayVaginal temperatures are about 0.2-0.4oF higher than rectaltemperatures
  22. 22. Summer to winter ratios for conception rate in Israeli herds as affected by production level and intensity of cooling (Flamenbaum and Galon, 2010) High production Low production Intensive Moderate Intensive ModerateConception cooling cooling cooling coolingrate (%)Winter 39 39 40 39Summer 19 12 25 3Summer:winter 0.49 0.31 0.62 0.08ratioIntensive – wetting/fans 10X/d Moderate wetting/fans 3X/dValues for milk yield are 0.96-1.03 for intensive cooling and 0.84-0.90 for moderate cooling
  23. 23. Take Home MessagesCool 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 worthwhileDon’t just cool lactating cowsheifers and dry cows as wellMeasure how effective cooling is Body temperatures Summer: winter ratios
  24. 24. Supported by Agriculture and Food Research Initiative Competitive Grantno. 2010-85122-20623 from the USDA National Institute of Food andAgriculture