This document discusses thermoregulation and rules related to how animals regulate body temperature. It describes two main types of thermoregulation - ectothermic animals that rely on external heat sources and endothermic animals that generate internal heat. Four ecological rules are outlined that describe how body size, pigmentation, hair/fat layers, and appendages vary between species in different climates. The document then discusses heat stress in animals and strategies to manage it, including providing shade, altering milking times, ensuring access to water, modifying diets, and supplementing nutrients.

1. Rules of thermoregulation

2. THERMOREGULATION
Thermoregulation is the ability of an organism to
keep its body temperature within certain
boundaries, even when the surrounding
temperature is very different

3. TYPES OF THERMOREGULATION
Ectothermic Animals
Absorb heat from their
surroundings
Many fish, most amphibians,
lizards, most invertebrates
Endothermic Animals
Derive body heat mainly from
their metabolism
Birds, mammals, a few reptiles
and fish, many insects

4. Ecological rules of
thermoregulation
1. ALLEN’S RULE
2. BERGMANN’S RULE
3. GOLGER’S RULE
4. WILSON’S RULE

5. ALLEN’S RULE
▣ Allen's rule is a biological rule posited by Joel Allen in 1877
“endotherms from colder climates usually have shorter
limbs (or appendages) than the equivalent animals from
warmer climates”
Jackrabbit- long ears, legs and
face
Arctic hare- short ears, legs and
small face

6. BERGMANN’S RULE
▣ Given by Christian Bergmann
▣ Bergmann's Rule asserts that geographic races of a
species possessing smaller body size are found in the
warmer parts of the range, and races of larger body size in
cooler parts

7. GOLGER’S RULE
▣ It was named after the zoologist Lambert Golger
Golger's Rule is a zoological rule which states that within a
species of endotherms, more heavily pigmented forms tend
to be found in more humid environments, e.g. near the
equator

8. WILSON’S RULE
▣ Animal living in the arctic region have thick layer of
subcutaneous fat compared to lean skin of animals in
tropical habitats
▣ Animals have longer hairs in arctic region as compared to
hotter climate animals
▣ For e.g. sheep and goats in colder climate have long hairs
and thick subcutaneous fat than hot climate animals

9. HEAT STRESS
▣ Heat stress occurs in animals when there is a imbalance
between heat production within the body (gain) and its
dissipation from the body (loss)
▣ Increased ambient temperature may lead to enhanced
heat gain as compared to heat loss from the body and
cause heat stress in animals.

10. CAUSE FOR THERMAL STRESS
▣ Animal’s inability to dissipate sufficient heat to maintain
homeothermy and homeostasis
▣ High ambient temperature & relative humidity
▣ High radiant energy
▣ increase in air temperature

11. HEAT STRESS
▣ Heat stress make animals susceptible to diseases
▣ Heat stress can be calculated using temperature humidity
index(THI)
▣ THI > 72 cattle is under heat stress
THI = (0.8*Tdb)+[(RH/100)*(Tdb-14.4)]-46.4
Tdb : Dry bulb temperature in °C
RH : Relative humidity in %
[Mader et al., 2006]

12. EFFECT OF HEAT STRESS ON DAIRY CATTLE
THI Stress Level Comments
< 72 None
72 – 79 Mild Dairy cows will adjust by seeking shade, increasing respiration rate and
dilution of blood vessels. The effect on milk production will be minimal
80 – 89 Moderate Both saliva production and respiration rate will increase. Feed intake may
be depressed and water consumption will increase. There will be an
increase in body temperature. Milk production and reproduction efficiency
will be decreased.
90 – 98 Severe Cows will become uncomfortable due to high body temperature, rapid
respiration and excessive saliva production. Milk production and
reproduction efficiency will be markedly decreased.
> 98 Danger Potential cow death can occur

13. HOW CAN WE MANAGE HEAT STRESS???
Shades and Cooling
▣ Cheapest way to avoid heat stress in animals
▣ Shades reduce the heat exposure and cooling by fan and water sprinklers reduces the
amount heat accumulation in the body

14. Milking times
▣ Milking the cows in the afternoon may add to their
existing stress
▣ Delaying evening milking until dusk may increase milk
yield more than half a litre per day
▣ On hot days milk and feed animals before 8 AM
▣ In hot summer months sprinkling of dairy animals before
morning and evening milking period can be a fruitful
strategy to bring down the effect of heat stress on
production

15. Plenty of drinking water
▣ Allow cows to drink plenty of cool and clean water in hot
summer months- twice the water what cows usually
needs in a day
▣ Make sure that cows have access of cool drinking water
where ever they are during the day
▣ Large volume concrete troughs help keep drinking water
cool
▣ We may avoid running black plastic pipes along the
ground, as water will become hot

16. Nutritional Approach
▣ Provide more amount of green (green fodder, silages)
than dry roughages will increase the intake of feed,
nutrient digestibility and energy level in heat stressed
animals
▣ During summer period, it is recommended that 75 % of
green fodder feeding
▣ Feeding of total mixed rations to avoid selective feeding
and increase the energy density of diet
▣ Increase the feeding frequency during cooler period of
the day

17. ▣ Feeding of by-pass nutrients (fats, protein and limiting
amino acids) will improve nutrient density and availability
for better milk production
▣ supplement nutrients which play role as antioxidants such
as Vitamin C, A and E, zinc and chromium can be used to
alleviate the cell oxidative damage of environmental
stress and to improve the nutrient utilization for
productivity
▣ electrolytes such as Na+, K+, and Cl- in the form of
bicarbonate or carbonate and salt supplementation
maintains the acid base balance which is disturbed during
evaporation of heat by more respiration (panting),
sweating and salivation and helps for proper body
functions