Heat Stress Effects - Issues & Questions

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Heat Stress Effects - Issues & Questions

  1. 1. HEAT STRESS EFFECTS: ISSUES & QUESTIONS DON SPIERS UNIVERSITY OF MISSOURI-COLUMBIA
  2. 2. WHAT IS STRESS? (Initial Question)
  3. 3. Stress = the environment or stimulus (same for everyone)Strain = the effect or response (different for everyone)
  4. 4. “It’s not stressthat kills us, itis our reactionto it.”
  5. 5. “I cannot, and should not, be cured of my stress but merelytaught to enjoy it” Hans Selye, l950
  6. 6. What is heatstrain?
  7. 7. Impaired Functions (the short list)1. Drop in production2. Increased days open3. Depressed immune system4. Decreased fertility
  8. 8. THE COSTAnnual losses in the USdue to heat stress equal$1.7 billion.Dairy = $897 millionBeef = $369 million
  9. 9. PHYSIOLOGICAL CHANGES1. Thermal Status 2. General Effects 3. Immune Condition 4. Nutritional Status 5. Behavior 6. Endocrine 7. Reproductive Status
  10. 10. Heat Stress - Physiological Strain Thermal Status 1. ↑ Core Body Temperature – rumen – tympanic – intraperitoneal A. Total Body Heat Content 2. ↑ Respiration Rate and Respiratory Evaporative Heat Loss 3. ↑ Skin Temperature, Blood Flow, and Sweat Rate A. ↓ Blood Flow to Internal Organs 4. ↑ Salivation, Drooling, and Panting Rates 5. ↓ Metabolic and Heat Production Rates 6. ↓ Heat Loss via Radiant, Conductive, and Convective Avenues 7. ↑ Dehydration
  11. 11. Heat Stress - Physiological Strain General 1. ↑ Impact Other Stressors 2. ↑ Heart and Pulse Rates 3. ↑ Hyperventilation A. ↓ Blood Carbon Dioxide B. ↓ Blood Bicarbonate C. ↓ Blood Buffering Capacity D. ↑ Respiratory Alkalosis 4. ↑ Urinary Sodium and Bicarbonate Excretion 5. ↓ Hepatic Portal Blood Flow 6. ↑ Hepatic Vitamin A Storage 7. ↑ General Vitamin E Deficiency
  12. 12. Heat Stress - Physiological Strain Immune Status 1. ↓ Immune Function 2. ↑ Susceptibility to Parasitic and Nonparasitic Diseases 3. ↑ Mastitis 4. ↑ Somatic Cell Count 5. ↑ Plasma Antibody - Immunoglobulin Concentration 6. ↑ Death
  13. 13. Heat Stress - Physiological Strain Nutritional Status 1. ↓ DMI, Weight Gain or Growth, Condition Score, and Blood Glucose Level 2. ↑ Energy Requirement for Maintenance 3. ↑ Salivation A. ↓ Saliva to Rumen B. ↓ Salivary Bicarbonate Pool for Rumenal Buffering C. ↓ Rumen pH D. ↑ Acidosis 4. ↑ Potassium Loss from Skin 5. ↑ Dietary Requirements for Potassium and Sodium 6. ↑ Urinary Nitrogen Loss 7. ↑ Water Intake
  14. 14. Heat Stress - Physiological Strain Nutritional Status - continued 8. ↓ Rumination A. ↓ Gut and Rumen Motility B. ↓ Gut Passage Rate C. ↑ Gut Fill D. ↓ Rumen Volatile Fatty Acid Concentration E. ↑ Acetate to Propionate Ratio Milk Production 1. ↓ Milk Production 2. ↓ Mammary Blood Flow 3. ↓ Mammogenesis 4. ↓ Lactation Peaks 5. ↓ Milk Component Levels
  15. 15. Heat Stress - Physiological Strain Behavior 1. ↓ Grazing Time 2. ↑ Lethargy 3. ↑ Shadow or Shade Seeking 4. ↑ Body Alignment with Solar Radiation 5. ↑ Standing Time 6. ↑ Crowding Water Trough and Splashing 7. ↑ Agitation and Restlessness
  16. 16. Heat Stress - Physiological Strain Endocrine 1. ↓ Hormones Linked to Metabolism – Thyroxine, Somatotropin, Cortisol 2. ↑ Hormones Linked to Water and Electrolyte Metabolism – Antidiuretic Hormone, Aldosterone 3. ↑ Catecholamines – Epinephrine and Norepinephrine 4. ↑ Prolactin and ↓ Prolactin Receptor Numbers 5. ↑ Leptin 6. ↑ Insulin >> ↓ Blood Glucose
  17. 17. Heat Stress - Physiological Strain Reproductive Status 1. ↓ Breeding Efficiency and Conception Rate 2. ↑ Fetal and Postnatal Mortalities + ↓ Calf Birth Weight 3. ↓ Semen Quality A. ↓ Spermatogenesis B. ↓ Sperm Motility C. ↑ Percent Abnormal and Aged Sperm 4. ↓ Estrous Activity A. ↓ Estrous Duration B. ↓ Heat Detection 5. ↓ Uterine Blood Flow A. ↓ Placental Weight and Growth + ↑ Retained Placenta B. ↓ Gestation Period C. ↑ Labor and Delivery Difficulties
  18. 18. Heat Stress - Physiological Strain Reproductive Status - continued 6. ↓ Follicular Development A. ↓ Oocyte quality B. ↑ Multiple Ovulations and Twinning C. ↓ Corporea Lutea Size 7. Biochemical Changes A. ↓ Plasma LH B. ↑ Ketone and NEFA Levels at Calving C. ↓ Thyroxine During Pregnancy D. ↑ Plasma Progesterone During Late Gestation E. ↑ Prostaglandin Synthesis Rate and Level During Early Postpartum Period
  19. 19. CAN WE REDUCE THE PROBLEM FROM THE THERMAL STATUS PERSPECTIVE?
  20. 20. Influenced by Body Surface Area Body Coverings Influenced by Sources Water Exchange Blood Flow Calorigenic Hormones Food Environment: Temperature Production: Body Reserves Wind Humidity Milk Meat Rumen or Cecum Wool Fermentation Non-Evap. Evaporative Environment Cooling Muscular CoolingRadiation Respiration Activity MaintenanceConvection SkinConduction Light HEAT LOSS HEAT GAIN BulbsHypothermia Hyperthermia Normal Body Temperature
  21. 21. BIG PROBLEM METABOLISM ORHEAT PRODUCTION
  22. 22. 1 ADULT HUMAN = 1 - 100 WATT LIGHT BULB 1 LACTATING DAIRY COW = 16 - 100 WATT LIGHT BULBSBIG BOVINE PROBLEM = HUGE HEAT PRODUCTION
  23. 23. Occurs with reduction in feed intake.
  24. 24. AVENUESOF HEAT LOSS
  25. 25. Conductive, Convective, and Radiative ExchangesRequire a Temperature Gradient
  26. 26. CONDUCTION RADIATION CONVECTION LESS EFFECTIVE AS AIRTEMPERATURE APPROACHES SKIN TEMPERATURE
  27. 27. EVAPORATIVE EXCHANGE
  28. 28. Only Solution is Increase Evaporative Heat Loss
  29. 29. Heat Dissipation (kcal/m/hr) Surface Vaporization 140 Non-Evaporative Process2 120 Respiratory Vaporization 100 80 60 40 20 0 0 20 40 60 80 100 Ambient Temperature ( oF) Redrawn from Yeck and Kibler (1956) and Kibler and Yeck (1959)
  30. 30. BUT A CHALLENGE TO CHANGE ESPECIALLY FOR BEEF CATTLE AND GRAZING DAIRY COWS
  31. 31. MANY DIFFERENT LEVELS OF SENSITIVITY COMPLICATING FACTORS: 1. Breed 2. Age 3. Health 4. Gender 5. Geographic Location and Climate 6. Acclimation Duration
  32. 32. IS IT POSSIBLE TO PREDICT ANIMAL RESPONSE TO HEAT STRESS?1. Remove or provide extra care for “sensitive” animals A. Change environment B. Change animal 1. Reduce heat production 2. Increase heat loss2. Identify heat extremes in advance A. Change environment B. Change animal 1. Reduce heat production 2. Increase heat loss3. Acclimation Program
  33. 33. AMBIENTCONDITION ANIMAL Present THERMAL STATUS ANIMALPRODUCTIVITY
  34. 34. AMBIENT Extremely difficultCONDITION Why? Ambient condition = indirect Present stressor Does not account for “Complicating Factors” Temperature Humidity Index ANIMAL is an examplePRODUCTIVITY
  35. 35. AMBIENT CONDITION ANIMALImprovement THERMALWhy? STATUSAccount s for “Complicating Factors”Physiological Strain Index is an example
  36. 36. AMBIENTCONDITION ANIMAL Present THERMAL STATUS ANIMALPRODUCTIVITY
  37. 37. Critical Zone ?Performance or Health HYPERTHERMIA WEIGHT LOSS DYSFUNCTION DISEASE DEATH Stress or Strain
  38. 38. Young’s Modulus of Elasticity = object or substancestendency to be deformed elastically (i.e., non-permanently)when a force is applied to it.The elastic modulus of an object is defined as the slope of itsstress-strain curve in the elastic deformation region: Elasticity = Stress/Strain Thomas Young
  39. 39. “If it were possible to measure quantitatively allthe strains responding to a given stress, wecould devise a type of Young’s Modulus ofElasticity (stress/strain). The reciprocal of this(strain/stress) would represent the additivecompliance of animals and might be called anindex of adaptation. This index could be of valueboth in determining the degree of adaptationachieved by an animal after a given period ofexposure to the stress and in determining whenadaptation is complete. It might also be useful incomparing the degree of adaptation achieved bydifferent species under similar conditions.“Melvin FreglySymposium Conducted by The NationalAcademy of Sciences-National ResearchCouncil August, 1966

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