HEAT STRESS EFFECTS: ISSUES & QUESTIONS

1. HEAT STRESS EFFECTS: ISSUES & QUESTIONS DON SPIERS UNIVERSITY OF MISSOURI-COLUMBIA

2. WHAT IS STRESS? (Initial Question)

3. Stress = the environment or stimulus (same for everyone) Strain = the effect or response (different for everyone)

4. “It’s not stress that kills us, it is our reaction to it.”

5. “I cannot, and should not, be cured of my stress but merely taught to enjoyit” Hans Selye, l950

6. The cow is a furnace

7. Birds are ‘heat stressed’ if they have difficulty achieving a balance between body heat production and body heat loss. This can occur at all ages and in all types of poultry. In the ‘thermoneutral zone’, birds can lose heat at a controlled rate using normal behaviour. There is no heat stress and body temperature is held constant.

8. When conditions mean the ‘upper critical temperature’ is exceeded, birds must lose heat actively by panting. Panting is a normal response to heat and is not initially considered a welfare problem. But as temperatures increase, the rate of panting increases. If heat production becomes greater than ‘maximum heat loss’ either in intensity (acute heat stress) or over long periods (chronic heat stress), birds may die. The body temperature of the broiler must remain very close to 41 C (106 F). If body temperature rises more than 40 C above this, the bird will die

9. Three normal methods of heat loss are listed below. Birds modify their behaviour to stay in the ‘thermoneutral zone’. Radiation – Heat will be lost from the body by radiation if the surrounding surfaces are below bird surface temperature. Conversely hot walls and roofs may radiate heat to the bird surfaces.

10. Convection – heat loss will occur from the natural rise of warm air from around a hot body. Providing moving air can assist convection, but only if the air moves fast enough to break down the boundary layer of still air that surrounds the body. Conduction – heat will transfer from one surface in contact with another surface, for example, if the birds are seated on litter that is cooler than their bodies. However, the litter immediately under the birds soon assumes a temperature close to that of the body.

11. After a bird can no longer maintain its body heat balance by one of these three methods (upper critical temperature), it must use “evaporative heat loss”, or panting. Evaporative heat loss, whilst essential to the bird, does not contribute to heating the house. ● Evaporation – This is very important at high temperatures as poultry do not sweat but depend on panting. This is only effective if the humidity is not too high. Hot, humid conditions are therefore much more stressful than hot dry conditions.

13. Birds will try to re-establish their heat balance with the surrounding by changing their normal behaviour. Birds may: ● Try to move away from other birds. ● Move against cooler surfaces, such as the block walls or into moving air streams. ● Lift their wings away from their bodies to reduce insulation and expose any areas of skin that have no feathers. ● Elect to pant slowly. ● Rest to reduce heat generated by activity. ● Reduce feed intake. ● Increase water consumption. ● Divert blood from internal organs to the skin, which darkens skin colour. ● Begin fast panting.

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17. Negative Impact of Heat Stress • Milk Production • Reproduction • Health • Nutrition • Behavior • Depressed immunes system function

18. The Hot Climate • The question is • Which of the many climatic factors have to be taken into consideration for a heat tolerance test?

19. The Hot Climate • The principal component factors • Temperature, humidity, wind and solar radiation. • Impose strain on animal's internal environment • Affect their health, reproductively, and eventually their productivity • They should all be included in a HTI either in single or in combination. • Each climatic factor affects body in a different way, • Specific structures and mechanisms of the body.

20. The Hot Climate • High environmental temperature, • Interferes with the dissipation of body heat by convection and radiation if does not exceed body temperature • Which emphasizes the importance of factors • Ratio of body surface to body mass, • Circulation of the blood • Body thermal gradient.

21. The Hot Climate • High air humidity • Interferes with dissipation of body heat by evaporation. • It thus plays a role in evaluating an animal's capacity for evaporative cooling by sweating and panting. • DisAdv. • Minor importance in a non-sweating or non-panting animals

22. The Hot Climate • Wind • Promotes dissipation of body heat by convection • Assists evaporation. • Large surface area of an animal • Higher its rate of skin evaporation • More benefit from the cooling power of wind.

23. The Hot Climate • Solar radiation • Imposes a heat load on the body by transferring energy to it from outside. • in contrast to the other three • Allows a determination the animal with capacity for absorbing\reflecting radiation, • Largely dependent on the characteristics of its skin and hair coat. • A glossy, light colored coat Vs dull, dark coat

24. The Hot Climate • Since all these climatic factors can affect the animal's thermal balance, it would appear desirable to express them jointly as a single figure, • Adv. • Different climates would be compared • Various attempts have been made to combine two or more climatic factors into a single index.

25. Water Intake • Under thermal neutral conditions lactating cows will drink 35 g/day • Water intake increases 1.2 to 2.0 fold during heat stress!! • Need about 3.5 linear inches of drinking space per cow in housing areas • Multiple locations • Need water troughs going to and from the parlor • 10% of water consumption Smith et al

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32. Response to Shade • 1.8 to 4.1 kg of milk/cow/day • Design of shades in dry lots is important • Orientation of naturally ventilated freestall barns is critical • Sun angles Animal Science Department - College of Agriculture and Life Sciences

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34. Two Ways to Cool Cows • Cool the Cow • Cool the Air Smith et al

35. Cooling the Cow • Soak the cow and dry the cow • Combination of soakers and fans • Soak the cow until the skin is wet • Evaporate the water off the skin • Kids at the pool on a hot windy day Smith et al

36. Locations • Holding pens • Exit lanes • Feedlines Smith et al

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42. Exit Lane Cooling • Nozzles activated by cow • 3 nozzles, 8 gallons per minute • Low cost • Additional 15-25 min. cooling/milking Smith et al

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50. Animal Science Department - College of Agriculture and Life Sciences