Animal’s Heat Tolerance It’s Concept and Measurement

1. Animal’sHeat Tolerance It’s Concept and Measurement Presented by SAMARA E. M. A. B.V.M.&S., R.A., and M.Sc. Student

2. Introduction • Heat • Form of Energy • Byproduct of all metabolic processes • Measured as Temperature • Expressed in units called calories or joules • Thermal vs. Heat

3. Introduction • Body Temperature • Rectal vs. Core Body Temperature • Balance between heat input and output • Thermal Steady State • Heat input vs. Heat output  HP + HG = HL + ∆C • Homeothermsvs.Poikilotherms

4. Introduction • Heat Stress • Animals stress response • Homeostatic mechanisms counteract stresses • Genetic vs.Physiological mechanisms • Thermo-physiological responses • Behavioral vs. Non-Behavioral response. • Homeostasis vs. Homeorhetic mechanisms

5. (Shearer and Beede, 1991)

6. Introduction • Adaptation vs. Heat tolerance • Phenotypic vs. Genotypic adaptation • Trait (character), Process, and Compensation Changes • Acclimation vs. acclimatization • Body Function vs. Structure

7. Introduction • Adaptation vs. Heat tolerance • The basic concepts of natural selection • Fitness and environment. • Every animal process is a function of heredity and environment. • Heat tolerance process as an aid to selection

8. Heat tolerance (HT) • The ability of the body to endure the impact of a hot environment without suffering ill-effects. • "ill-effects" • Animal Husbandry Man • Poor performance with respect to grazing, thrift and milk yield • Veterinary Practitioner • Low fertility and high proneness to disease • Physiologist • Displacement from the normal of body functions • Body temperature, sweating, and respiratory activity.

9. Heat tolerance (HT) • Different people, different criteria, different angles of view • which makes any comparison accompanied with difficulties both fundamental and practical. • It would appear therefore to … • Find a way ofassessing an animal's innate overall capacity to cope successfully with a hot environment • Determine the animal's that inherent heat tolerance trait.

10. HTT ‘tests’ or HTI ‘indices’ • To design a HTI, three main factors have to be considered … • The hot climate(the stress producing agent) • The animal body(the target) • A numericalscale for expressing the effect of the hot climate on the animal body. • In form of test or index

11. Heat tolerance (HT) • Heat tolerance is a complex phenomenon; • The impact of one complex system “the thermal environment” on another complex system “the animal's body”. • The Numerical Scale in form of test cannot take into consideration • All climatic elements and All animal characters.  Only the most important/suitable factors has to be selected.

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

13. The Hot Climate • HTI must be carried out in a standard thermal environment. • In order to give reproducible and comparable results • This is difficult to achieve in the field • Environmental Chambers • Controlled atmosphere of a hot room • Preferable • Has its limitations

14. The Hot Climate • Animals tested simultaneously in the same geographical area ranked according to their heat tolerance • Adv. Allows selection of those animals • DisAdv. Not comparable with another breed in another climate • The total heat load imposed on an animal should be large enough to evoke a pronounced response, but not so large as to cause damage.

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

16. The Hot Climate • The principal component factors • Temperature, humidity, wind and solar radiation. • Impose strain on animal's internal environment • Affect their health, reproductivity, 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.

17. 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.

18. 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

19. 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.

20. 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

21. 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.

22. ◄ Heat Load Index (HLI) ► • Incorporate the effect of all four climatic variable • Gaughan et al. (2002)calculated the HLI using these three equations … [BGT = 1.33Ta – 2.65 √Ta + 3.21 log(SR + 1) + 3.5] ………..…... (1) [HLI = 10.66 + 0.28RH + 1.3BGT – WS] …………………………(2) [HLI = 8.62 + 0.38RH + 1.55BGT – 0.5WS + exp(-WS + 2.4)]…..(3) Where; BGT = black globe temperature; Ta = dry bulb temperature (°C); SR = solar radiation (W/ m2); RH = relative humidity (%); WS = wind speed (m /s)

23. Animal Body • The questions is, • What is the relation of some selected body structures to heat tolerance? • Which body functions are eligible for use as criteria in a heat tolerance test?

24. Animal Body Structure • Surface/mass ratio • Texture and Color of the hair coat • In general … • A large relative body surface, in particular large body appendages (dewlap, navel fold, ears, tail), with movable skin • Short glossy coat and a well pigmented • Associated with a high heat tolerance.

25. Animal Body Structure • HT and animal body correlations have great practical value for several reasons. • Determined very easily • High degree of heritability which facilitates their genetic fixation by breeding • Structural features correlated well with physiologicalresponses indicative of an animal's heat tolerance • The knowledge of these features may enable a breeder to predict the future heat tolerance of a young animal

26. Animal Body Structure • Surface/mass ratio • McDowell, Lee & Fohrman (1953) • Did not find significant differences in the surface/mass ratio between European and Zebu cattle, which otherwise differed in heat tolerance. • McDowell (1958) • Surgical removal of hump and dewlap in Red Sindhi bulls did not depress their heat tolerance.

27. Animal Body Structure • Texture and Color of the hair coat • Bonssma (1949) • Established a clear relationship between coat texture and heat tolerance • Animals with a sleek coat withstand heat better than animals with a woolly coat. • Dowling (1959) • A high proportion of modulated hair fibers in the coat favors heat tolerance • Turner & Schleger (1960) • Described a subjective method for scoring of cattle coats which seems to afford a good prediction of cattle performance in a hot climate. • “Felting test”

28. Animal Body Structure • However, • It should be realized that any such structure is not eligible as a criterion in a heat tolerancetest • Because it does not change measurably during exposure to an acute standard heat stress. • It just, possess prognostic value

29. Animal Body • The questions is, • What is the relation of some selected body structures to heat tolerance? • Which body functions are eligible for use as criteria in a heat tolerance test?

30. Animal Body Function • A hot environment affects the entire animal. • This means that a great number of physiological activities undergo specific changes. • The information driven from a heat tolerance test should thus be expected to become more complete the larger the number of activities observed.

31. Animal Body Function • However, the use of a large number of criteria in a heat tolerance test has the disadvantage of complicating the performance of a test. • large the number of animal characters undesirable, more difficult and less effective in selection • It is necessary to make an optimal choice among the various body functions.

32. Animal Body Function • Nominated body function • Respiratory activity • Cardio-vascular activity • Cutanous evaporation • Body temperature

33. Animal Body Function • Body function requirements to be eligible as a criterion for a heat tolerance test; • It should be meaningful • Directly related to the body's thermoregulation • Representative of the strain on the animal in a hot environment. • It should respond to environmental heat in a ready and reproducible way • Show a clear dose/response relationship.

34. Animal Body Function • Body function requirements to be eligible as a criterion for a heat tolerance test; • Its measurement should be accurate, quick, simple, and inexpensive. • It should have a normal base line • Show relatively little variation in hot vs. cold envi. • It should be applicable also in the young animal • Allowingearly prediction of an adult animal's heat tolerance.

35. Animal Body Function • Body temperature is the best criterion of an animal's heat tolerance among the various body functions… • It is physiologically meaningful; • Representing the resultant of all heat gain and heat loss processes of the body • It is relatively stable in a temperate environment • It responds readily and in a repeatable way to heat stress • It is easily and accurately measured.

36. Animal Economic Trait • Productive performance • Milk vs. Beef production • Related to heat tolerance in two ways: • They involve the generation of extra heat, which reduces the capacity for heat tolerance. • They become depressed when the environment is very hot, which favors heat tolerance.

37. Animal Economic Trait • Cartwright (1955) • Found weight-gain in summer a moreuseful indicator of heat tolerance than rectal temperature, respiratory rate and heart rate, • Warwick & Kincaid (1959) • Postulated that the selection of beef cattle on the basis of production automatically includes selection for heat tolerance.

38. Animal Economic Trait • Although this approach has much to recommend it, it also has its limitations, especially with respect to milk yield. • Cannot be tested in young animals. • Excludes prediction of an animal's future performance from a calf hood index.

39. Animal Economic Trait • Milk yield is affected by a hot environment in an indirectway • Decline in milk yield is preceded by a decline in voluntary food intake. • There is no immediate effect of hot weather on milk production as long as food consumption is not affected • Food with a high fiber content vs. a high proportion of concentrates

40. Animal Economic Trait • It may be said that • Productive performance seems to be useful as an indicator to heat tolerance with beef cattle, • Less useful in these respects with dairy cattle.

41. The NumericalScales • Expressing the effect of the hot climate on the animal body. • In form of test or index • There are two ways of expressing an animal's heat tolerance.

42. The NumericalScales • How much does a certain body function change when the animal is exposed to a standard hot environment? • This is the commonly used way • Expresses heat tolerance in terms of animal response • Relatively easy to perform • Give a precise numerical answer • Limited in its interpretation

43. The NumericalScales • Which heat load must be imposed on an animal in order to evoke a standard change in body function? • This way is less common with respect to climate • Expresses heat tolerance in terms of a thermal environment • Less easy to perform • Less precise in its result • It is more meaningful in its interpretation.

44. ◄ Water Expenditure Test ► • Rhoad (1940) • Postulate that under field conditions measured parameters indicative of an animal's water loss through various channels, namely: • Respiratory rate, as an index of moisture loss from the respiratory tract • Loss of moisture from selected skin areas; • Nitrogen concentration of the urine, as an index to water expenditure through the kidneys; • Moisture content of the faeces, as an index to water expenditure through the excreta.

45. ◄ Water Expenditure Test ► • Procedure • Measured these parameters in 1 to 10 hours with an average of 3 hours. • Water at atmospheric temperature was available at all times.

46. ◄ Water Expenditure Test ► • Advantages .. • This is a useful approach to an important side of the heat tolerance problem • Water loss • Rhoad has been able to demonstrate with his method clear breed differences.

47. ◄ Water Expenditure Test ► • Disadvantages .. • It is too complicated to be adopted as a heat tolerance test proper. • It does not measure an animal’s water loss accurately enough. • Rhoaddid not condense the data into any formula. • For judging the “Efficiency of heat disposal" Rhoad relied on the behaviour of rectal temperature, • which he extended to the Iberia heat tolerance test.

48. ◄ Iberia Heat Tolerance Test► • Rhoad (1944) • Determines how much the rectal temperature of an animal exceeds 101°F (38.3°C) when ……...? • Average rectal temperature of cattle = 101°F

49. ◄ Iberia Heat Tolerance Test► • Procedure • Animals exposed in the open field to the thermal conditions of a calm clear day with a shade temperature between 85 and 95°F (29°and 35°C) • The rectal temperature measurements are taken at 10.00 and 15.00 hours on three consecutive days and the results averaged. • Using the formula: { 100 - [10*(mean rectal temperature – 101) }

50. ◄ Iberia Heat Tolerance Test► • Procedure • Respiratory rate, • Counted at the same time, • Differentiate between two animals showing the same rise in rectal temperature. • The result is expressed as a percentage of maximal efficiency in maintaining rectal temperature at 101°F. • The animal with the least rise in rectal temperature (and the lowest respiratory rate) is considered the most heat tolerant.