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Heat Stress in Dairy Cattle

Heat Stress in Dairy Cattle. Akrum Hamdy. Introduction. All animals have a zone of thermo neutral temperatures conducive to normal function The upper critical temperature is where the effects of heat stress start to appear. Heat Stress.

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Heat Stress in Dairy Cattle

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  1. Heat Stress in Dairy Cattle • Akrum Hamdy

  2. Introduction • All animals have a zone of thermo neutral temperatures conducive to normal function • The upper critical temperature is where the effects of heat stress start to appear

  3. Heat Stress • The point at which a dairy cow (or other animal) cannot dissipate an adequate quantity of heat to maintain body thermal balance or normal body temperature

  4. Source: NRC, 1981

  5. Temperature Humidity Index (THI) • Includes both temperature and humidity in determining the point sat which heat stress may occur • A THI > 72 is considered to indicate heat stress in dairy cattle

  6. Example of the Interaction of Temperature and Humidity in Determining Heat Stress Potential in Dairy Cattle

  7. All of These = THI of 72

  8. How Do Cows Respond to Heat Stress? • Higher body temperatures • Increased respiration rates (>70/hour) • Less activity • Increased water intake • Seek shade • Look for cool areas in the barn

  9. What Happens Metabolically? • Energy requirements for maintenance increase - Increased respiration rate -More blood flow to the skin - Less blood flow to body core - May increase by 20-30%

  10. What About Dry Matter Intake? • Dry matter intake decreases in cows subjected to heat stress - May drop 10-20% in commercial herds - Becomes variable - May be short or long-term

  11. How About Milk Production? • Decreases due to: - More energy for maintenance - Less energy for productive functions - Lower dry matter intake - Alterations in nutrient use - Can drop 10 to > 25%

  12. What Happens to Reproduction? • Usually decreases in heat stress situations • Estrus intensity and length decrease • Fertility rate decreases • Ovarian follicle growth decreases • Increase early embryonic death • May affect fetal growth

  13. What Determines the Severity of Heat Stress? • Actual temperature and humidity • Length of the heat stress period • Degree of cooling that occurs at night • Ventilation and air flow • Cow factors (size, milk production) • Water availability • Hair coat depth

  14. Which Cow Will Be Affected More by the Sun?

  15. Heat Stress, Dry matter Intake and Milk Production • Used the CNCPS ration model to predict dry matter intake and milk production • Cow = 1,400 lbs producing 80 lbs. of milk • Varied temperature and humidity

  16. Conditions for Each Run 1 lb. of fat was added to the ration in Run 5

  17. Maintenance Energy Required – Mcal

  18. Predicted Dry Matter Intake, lbs.

  19. Predicted Milk Production, lbs.

  20. Economic Impact of Heat Stress • St-Pierre et. al., 2003 • Estimated costs of heat stress for both the US and each state • Included dairy cattle, beef cattle, swine and poultry • Yearly cost = $2.4 billion dollars

  21. Total Loss by Animal Type, %

  22. Heat Stress Loss Estimates by State, Millions of Dollars

  23. What Can We Do to Minimize the Effects of Heat Stress? • 2 basic approaches - a. Adjust the ration b. Adjust the environment in which the cow lives

  24. Ration Adjustments • Need to keep the animal healthy!!! • Select higher quality forages and more digestible feed ingredients (lower heat production during digestion) • Consider added fat - Concentrated energy source - Low heat of digestion

  25. Ration Adjustments - 2 • Replace some forage with non-fiber byproduct feeds (beet pulp, soy hulls) • Minimize excess total and rumen degradable protein (requires energy to excrete from the body) • Consider buffers, yeast and added minerals

  26. Feeding Management Changes • Fresh, palatable high quality feed should always be available • Uniformity of mixed and delivered rations • Minimize feed sorting • Shift feeding times to cooler part of the day

  27. Water • Intake may increase by 20 to >50% during heat stress • Clean, fresh water always available • Adequate watering devices or space (minimum of 2-3 inches per cow) • Make sure pressure is adequate to refill waterers

  28. Housing and Facility Adjustments • Minimize overcrowding • Minimize time in the holding area • Is shade available? • Can air flow be increased with fans? • Can misters or sprinklers be installed to wet the cow’s skin?

  29. What Heat Stress?

  30. THI Thresholds for Other Species • Beef cattle = 72 – 75 o F • Swine = 72 – 74 o F • Poultry = 70 – 78 o F

  31. Summary • Heat stress can decrease animal production, reproduction and profitability • Ration, feeding management and housing alterations can be made to lower the effect of heat stress

  32. Summary - 2 • The challenge is to balance investment cost versus projected returns • In the Northeast, we have a low number of heat stress days • New facilities being built are incorporating housing components to minimize the effect of heat stress

  33. What Heat Stress?

  34. Monsanto

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