This document discusses the effects of climate on reproduction in cattle. It covers: 1) Different climate types (tropics, subtropics, temperate) and how they affect cattle thermoregulation. 2) The concept of heat stress and how temperature and humidity are combined in the Temperature Humidity Index (THI) to assess heat stress levels. 3) How heat stress reduces cattle performance through impacts like decreased feed intake and milk production, and increased respiration rate. It also discusses effects on reproduction like reduced conception rates.

1. Obstetrics and Genital Diseases
Ther 707
4(2-2)
Lec 27: Effect of Climate on
Reproduction
(Youngquist & Morrow)
Dr Mian Abdul Sattar

2. Climate types
• Tropics
• Subtropic
• Temperate

3. Tropics
The tropics is a region of the earth
surrounding the equator. It is limited in
latitude by the tropic of the Cancer in the
northern hemisphere and the tropic of the
Capricorn in the southern hemisphere. These
latitudes correspond to the axial tilt of the
earth
The tropics include all the areas on the Earth
where the sun reaches a subsolar point, a
point directly overhead at least once during
the solar year

4. Subtropics
• The subtropics are located
roughly between the tropic
circle of latitude (the tropic of
the Cancer and tropic of the
Capricorn) and the 35th parallel
in each hemisphere

6. Thermoregulation
• The cow maintains a constant body
temperature of approximately 38.5°C by
matching internal heat production with net
loss of heat to the environment.
• Primary sources of heat loss
– Breathing
– Evaporation from skin

7. Heat Stress
• Heat Stress:Animal can not dissipate an adequate heat to
maintain body thermal balance
• Climatic factors
– Temperature
– Humidity
To determine perceived equivalent body Temperature (Felt
air temp); temp and humidity are combined in one equation
known as Temperature Humidity Index.

8. THI:
(Dry bulb Temp °C) + (0.36*dew point Temp
°C) + 41.2
Temperature Humidity Index
For exotic Cow
Heat stress begins when THI is >72.
THI  effectively assesses the effect of heat
stress on livestock

9. Dew Point Temperature
• The dew point is the temperature at
which water vapour condenses into
liquid water. It is important to know
the dew point because it is the
temperature at which clouds form.
When air rises from the ground, it
cools until it reaches its dew point and
then clouds form.
• http://www.weathersa.co.za/web/index.php/
corporate?id=184

10. Dew Point Temperature
• To calculate dew point temperature we use
a wet and dry bulb thermometer. This
consists of two thermometers placed side by
side.
• The temperature difference between the two
thermometers tells us how much moisture is
in the air (Relative humidity). The greater
the difference the drier the air.
http://www.weathersa.co.za/web/index.php/co
rporate?id=184

12. THI
• THI= (1.8xT+32) - ((0.55-
0.0055xRH) x (1.8xT-26))
• Where T=Temperature and
RH=Relative Humidity
• http://www.dairynz.co.nz/page/pageid/2145
857378/Temperature_Humidity_Index_THI
_Calculator

13. • THI 68 for Friesians/ 75 for Jerseys (equivalent to
21 and 25.5°C respectively at 75% relative
humidity) ……..cows begin ………. heat stress.
(Reduction in feed intake and a drop of around
10g milksolids per day per unit increase in THI
(Bryant et al. 2007).
• For example, an increase in THI from 68-78
would equate to a 100g drop in
milksolids/cow/day. Note that a drop in fat/protein
percentage occurs before a drop in yield or
milksolids is visible (Bryant et al. 2007).
http://www.dairynz.co.nz/page/pageid/2145857378/Temperat
ure_Humidity_Index_THI_Calculator

14. Animal changes in response to Heat Stress
– Elevated Body temp
– Increased Respiration rate
– Increased Heart rate
– Increased maintenance energy requirement
– Decreased feed nutritional utilization
– Decreased dry matter Intake
– Decreased milk production
– Decreased reproduction

15. Climate & Reproduction
• Suppression of Conception Rate (CR) in summer months
– June to August and up to November
– Sever in cows at or more than 30°C following breeding
– An 0.5°C increase in Ut. Temperature= 6-12 % drop in CR
• How thermal stress affects reproduction?
– Less pronounced estrus
– Reduced estrus duration
– Silent ovulation
– Fertilization normal but higher embryonic mortality
– Smaller proestrus rise of Estradiol
– Thermal stress reduces the uterine blood flow
– Higher periestrus Uterine temperature
– Reduces the placental and fetal wt.
– Reduces milk production

17. Possible mechanisms
Higher ambient temp adversely affects milk
production in the following ways:
• Panting incr
– CO2 expell more
– Saliva buffer power decr
– Ruminal pH decr (acidosis)
• Feed intake decr (direct effect on body)
• Rumination decr (direct effect on body)
• Drooling of saliva incr
– Less saliva to rumen so less buffering effect

19. THI
• Incr ACTH, incr cortisol, decr LH
• Decr thyroxin, decr metabolism
• Directly affecting spermatogenesis
• Directly affecting implantation
• Incr prolactin, decr GnRH

21. THI Stress Comments
72-79 Mild Cow seek shade, Respiration increases, dilation
of Blood Vessels, Milk decreased slightly
80-89 Moderate Salivation and Respiration increased, Feed
intake decreased, Water intake increased, Body
Temp. increased, Milk decreased, Reproductive
efficiency decreased
90-98 Sever Un-comfort, High body Temp, panting,
excessive saliva, Milk prod. And reproduction
markedly decreased
98 & above Danger Potential Cow death can occur

22. Severity of heat stress depends
• Environmental Temperature
• Humidity
• Length of heat stress period
• Night cooling degree
• Ventilation and air flow
• Breed
• Animal size
• Coat color and hair coat depth
• Water availability
• Level of Milk production

23. Mild – THI 75
28°C and 50% humidity or
30°C and 30% humidity
– THI 78
28°C and 65%humidity or
30°C and 45%humidity or
32°C and 30% relative humidity
High – THI 82 plus
28.2°C and 90% humidity or
30°C and 75% relative humidity
36°C and 30%humidity or

24. Sprinkle cows at
afternoon milking
Ensure adequate
buffers and minerals
in diet
Ensure free access to
cool drinking water
Sprinkle cows at both
afternoon and morning
milking
Increase grain/concentrate
feeding rate and feed
higher quality forage
Do all of the above, plus:
Use fans if insufficient air
movement
Make further alterations to
feeding management and the
diet as appropriate.
Take emergency measures
Temperature Humidity Index
• For exotic Cow
– Heat stress begins when THI is >72.
Moderate – THI 75
26°C and 65% humidity or
30°C and 30% humidity
High – THI 78
28°C and 80%humidity or
32°C and 30% relative humidity
High – THI 82 plus
28.2°C and 90% humidity or
30°C and 75% relative humidity
36°C and 30%humidity or

25. Effect of heat stress on estrus
– Reduced estrus duration
– Less pronounced estrus
– Increase undetected estrus percentage
• Heat stress reduce peripheral E2 Concentration so low response
of pituitary to GnRH
%
missed
estrus
Month of year

26. Effect during early pregnancy
• Heat stress can cause a reduction in dry mater
intake and may influence the uterine
environment by decreasing blood flow to the
uterus with consecutive increase of uterine
temperature.
• Heat stress can compromise the success of
gestation during the peri-implantation period to
the extent that a high temperature–humidity
index during Days 21–30 of gestation is a risk
factor for early fetal loss

27. Effect of heat stress on Pregnancy
• Pregnancy rate per insemination decreased
– Oocyte growth and maturation disturbed
• Embryonic survival compromised
• Uterine support decreased by lower P4 in serum
• Lower Interferon – by day 17 conceptus
Pregnancy
per
insemination
Month of year
An 0.5°C increase in
Uterine Temperature
results 6-12 % drop in CR

28. Effect of heat stress on Late Pregnancy
• Placental functions compromised by stress
• Less chances of abortion but low birth weight
• Low immunoglobulin transfer to neonate
• Mammogenesis compromised

29. Managemental strategies during heat stress
• Provide ample water
• 2 gallons water / 50 kg body wt
– Provide shaded areas
• 20-40 sq foot/animal
– Improve airflow
– Water mist
• Avoid to wet nearby feed
– Control flies

30. • Heat detection
– Night time observation
– detection aids
– Synchronization protocols
• Cow cooling
– shade, fans and evaporative sprinklers or misters
• AI , ET
• Genetic improvement
– Bos indicus

31. Summary
– Understand the principle of heat stress
– Low animal performance:
– Reduce feed intake
• less Milk
• less estrus
• lower fertility

32. General considerations
• Normally, saliva 100 litre per day
• Stress by cows can lead to 38% lower milk
yields
• Milk production normally decreases 50 –
120 gr./day
• Healthy cow breathes easily
– exhales 10 - 30 times per minute
– a calf exhales more (around 30)

33. • Management strategies
– Understanding the principle of heat stress
– Low animal performance:
– Reduce feed intake---less Milk---less estrus---lower fertility
– Possible Solutions:
• Economically improving microclimate of animal
– Well ventilated housing or use of trees
– Free access to fresh water
– Fans or Fans with spray nozzles
– Showering/ bath for animals or water pond/canal
– High energy feed in early hours and during night
– Extra care of bulls or use of AI
– Free access to loafing (feeding) areas with out concrete/brick
flooring
– Care of dry pregnant animals

34. Cow Comfort
• Housing
• Cooling
• Feeding & Watering
• Hygiene & Health Care

35. Housing
• Shed direction
• Airflow
• Stall type
• Flooring
• Facilitate Water intake
• Facilitate Feed intake
• Cooling equipment

36. Good ventilation important
• Optimum barn temperature 10ºC
• Temperature inside and outside must be nearly
the same (max 5ºC) ---> (no draft !!)
• For removal of harmful gases
– Carbon dioxide and ammonia
– cow exhales 12 ltr water vapour
• Air inlet (should be at least 150% of size of air
outlet opening)
• Air outlet

37. Cooling
• Airflow & Shade
• Sprinklers and fans
• Misting and fans
• Controlled Environment Sheds

38. Cooling
Fans and Sprinklers
• Fans placed in the barn (wind position?)
• Sprinklers right above the feeding table
• Soaking the herd 4 to 6 times per hour
• Constant fans

39. Provision of water
Water provider per 30 - 40 cows
• Dry cows 30 - 60 lt/day
• Cow 10 kg milk 30 - 70 lt/day
• Cow 30 kg milk 90 - 150 lt/day
• Cow 50 kg milk 100-200 lt day
• Calves < 1 year 5 - 15 lt/day
• Calves 1 - 2 year 15- 25 lt/day
• Bull for meat 20- 60 lt/day
• Sheep/goats 1,5 - 6 lt/day
– Dry cows --> individual water supply possible
• Temp: 7 – 15°C (temp 30 – 33°C increase intake with 3.4 –
6%)

40. Heart function and heartbeat
• Heart function is important
– 1 kg milk requires 400 litres of blood
• Heart rate
– normal rate: 60 - 80 beats a minute
– higher than 80 --> infection, heart loses its capacity
– Afflicted valves--> unable to process the
bloodstream-> heart oedema --> culling cow
• The heart can be found behind the left elbow
– Feel and count the heart-beat by using the arteries
• artery of the tail