heat stress effects: issues & questions don spiers university of missouri-columbia
TRANSCRIPT
Stress = the environment or stimulus
(same for everyone)
Strain = the effect or response (different for everyone)
Impaired Functions (the short list)
1. Drop in production
2. Increased days open
3. Depressed immune system
4. Decreased fertility
THE COST
Annual losses in the USdue to heat stress equal $1.7 billion.
Dairy = $897 million
Beef = $369 million
PHYSIOLOGICAL CHANGES
1. Thermal Status
2. General Effects
3. Immune Condition
4. Nutritional Status
5. Behavior
6. Endocrine
7. Reproductive Status
Heat Stress - Physiological Strain
Thermal Status
1. ↑ Core Body Temperature – rumen – tympanic – intraperitonealA. Total Body Heat Content
2. ↑ Respiration Rate and Respiratory Evaporative Heat Loss
3. ↑ Skin Temperature, Blood Flow, and Sweat RateA. ↓ 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
Heat Stress - Physiological Strain
General
1. ↑ Impact Other Stressors
2. ↑ Heart and Pulse Rates
3. ↑ HyperventilationA. ↓ Blood Carbon DioxideB. ↓ Blood BicarbonateC. ↓ Blood Buffering CapacityD. ↑ Respiratory Alkalosis
4. ↑ Urinary Sodium and Bicarbonate Excretion
5. ↓ Hepatic Portal Blood Flow
6. ↑ Hepatic Vitamin A Storage
7. ↑ General Vitamin E Deficiency
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
Heat Stress - Physiological Strain
Nutritional Status
1. ↓ DMI, Weight Gain or Growth, Condition Score, and Blood Glucose Level
2. ↑ Energy Requirement for Maintenance
3. ↑ SalivationA. ↓ Saliva to RumenB. ↓ Salivary Bicarbonate Pool for Rumenal BufferingC. ↓ Rumen pHD. ↑ Acidosis
4. ↑ Potassium Loss from Skin
5. ↑ Dietary Requirements for Potassium and Sodium
6. ↑ Urinary Nitrogen Loss
7. ↑ Water Intake
Heat Stress - Physiological Strain
Nutritional Status - continued
8. ↓ RuminationA. ↓ Gut and Rumen MotilityB. ↓ Gut Passage RateC. ↑ Gut FillD. ↓ Rumen Volatile Fatty Acid ConcentrationE. ↑ Acetate to Propionate Ratio
Milk Production
1. ↓ Milk Production
2. ↓ Mammary Blood Flow
3. ↓ Mammogenesis
4. ↓ Lactation Peaks
5. ↓ Milk Component Levels
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
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
Heat Stress - Physiological Strain
Reproductive Status
1. ↓ Breeding Efficiency and Conception Rate
2. ↑ Fetal and Postnatal Mortalities + ↓ Calf Birth Weight
3. ↓ Semen QualityA. ↓ SpermatogenesisB. ↓ Sperm MotilityC. ↑ Percent Abnormal and Aged Sperm
4. ↓ Estrous ActivityA. ↓ Estrous DurationB. ↓ Heat Detection
5. ↓ Uterine Blood FlowA. ↓ Placental Weight and Growth + ↑ Retained PlacentaB. ↓ Gestation PeriodC. ↑ Labor and Delivery Difficulties
Heat Stress - Physiological Strain
Reproductive Status - continued
6. ↓ Follicular DevelopmentA. ↓ Oocyte qualityB. ↑ Multiple Ovulations and TwinningC. ↓ Corporea Lutea Size
7. Biochemical ChangesA. ↓ Plasma LHB. ↑ Ketone and NEFA Levels at CalvingC. ↓ Thyroxine During PregnancyD. ↑ Plasma Progesterone During Late GestationE. ↑ Prostaglandin Synthesis Rate and Level During Early
Postpartum Period
Influenced by
Body Surface AreaBody CoveringsWater ExchangeBlood FlowEnvironment: Temperature Wind Humidity
Non-Evap.Cooling
Radiation
Convection
Conduction
EvaporativeCooling
Respiration
Skin
HEAT LOSS
Hypothermia HyperthermiaNormal
Body Temperature
Influenced by
CalorigenicHormones
Production: Milk Meat Wool
Muscular
ActivityMaintenance
Sources
Food
Body Reserves
Rumen or Cecum Fermentation
Environment
HEAT GAIN
Light Bulbs
1 ADULT HUMAN = 1 - 100 WATT LIGHT BULB
1 LACTATING DAIRY COW = 16 - 100
WATT LIGHT BULBS
BIG BOVINE PROBLEM = HUGE HEAT PRODUCTION
0
20
40
60
80
100
120
140
Hea
t D
issi
patio
n (
kcal
/m2/h
r)
0 20 40 60 80 100
Ambient Temperature ( oF)
Respiratory Vaporization
Non-Evaporative Process
Surface Vaporization
Redrawn from Yeck and Kibler (1956) and Kibler and Yeck (1959)
MANY DIFFERENT LEVELS OF SENSITIVITY
COMPLICATING FACTORS:
1. Breed
2. Age
3. Health
4. Gender
5. Geographic Location andClimate
6. Acclimation Duration
IS IT POSSIBLE TO PREDICT ANIMAL RESPONSE TO HEAT STRESS?
1. Remove or provide extra care for “sensitive” animalsA. Change environmentB. Change animal
1. Reduce heat production2. Increase heat loss
2. Identify heat extremes in advanceA. Change environmentB. Change animal
3. Reduce heat production4. Increase heat loss
3. Acclimation Program
ANIMALPRODUCTIVITY
Pre
sent
AMBIENT CONDITION
Extremely difficult
Why?
Ambient condition = indirect stressor
Does not account for “Complicating Factors”
Temperature Humidity Indexis an example
ANIMALTHERMALSTATUS
AMBIENT CONDITION Future
Improvement
Why?
Account s for “Complicating Factors”
Physiological Strain Index is an example
Per
form
ance
or
Hea
lth
EU
STR
ES
S G
OO
DS
WE
ET
SP
OT
Stress or Strain
DIS
TRE
SS
BA
D
DEATH
HYPERTHERMIAWEIGHT LOSSDYSFUNCTIONDISEASE
Critical Zone ?
Young’s Modulus of Elasticity = object or substance's tendency 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 its stress-strain curve in the elastic deformation region:
Elasticity = Stress/Strain
Thomas Young
“If it were possible to measure quantitatively all the strains responding to a given stress, we could devise a type of Young’s Modulus of Elasticity (stress/strain). The reciprocal of this (strain/stress) would represent the additive compliance of animals and might be called an index of adaptation. This index could be of value both in determining the degree of adaptation achieved by an animal after a given period of exposure to the stress and in determining when adaptation is complete. It might also be useful in comparing the degree of adaptation achieved by different species under similar conditions.“
Melvin Fregly
Symposium Conducted by The National Academy of Sciences-National Research Council August, 1966
Being healthy means being able to adapt to and overcome obstacles. It allows"a margin of tolerance for the inconsistencies of the environment." Health is a "regulatory flywheel of the possibilities of reaction" .
Normative beings are able to deal with conflicts in a way that leaves open the possibility of future correction. Any normality limited to maintaining itself, hostile to any variation in the themes that express it, and incapable of adapting to new situations does not represent health.
An organism is healthy to the extent that it is capable of adjusting these norms in the face of changing circumstances.
Georges Canguilhem