1. Heat Stress in Dairy Cattle Akrum Hamdy Akrum Hamdy

2. Introduction All animals have a zone of thermo neutral temperatures conducive to normal function 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 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 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 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 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

8. All of These = THI of 72 Temperature, o F Humidity, % 8415 8030 7750 7565 7295

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

10. 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% 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%

11. 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 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

12. 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% 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%

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

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

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

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

17. Conditions for Each Run Run Temp., F Humidity Night Temp. 1605050 2905060 3907060 4907075 5907075 1 lb. of fat was added to the ration in Run 5

18. Maintenance Energy Required – Mcal

19. Predicted Dry Matter Intake, lbs.

20. Predicted Milk Production, lbs.

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

22. Total Loss by Animal Type, %

23. Heat Stress Loss Estimates by State, Millions of Dollars State Loss, Million $ Dairy, % of Total Loss New York 24.998 Pennsylvania50.888 Vermont5.498 Maryland8.7586

24. 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 2 basic approaches - a. Adjust the ration b. Adjust the environment in which the cow lives

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

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

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

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

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

30. What Heat Stress?

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

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

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

34. What Heat Stress?

35. Monsanto