Summer (Heat) season causes number of deleterious effects on broilers and layers which ultimately reduces profitability. Summer (Heat) stress has been a serious concern for poultry producers as it directly leads to financial losses by impaired poultry performance.
What exactly happens to Poultry birds in heat stress?
Poultry birds become heat stressed when they have difficulty in achieving balance between body heat loss and body heat production, the normal body temperature of poultry being 41ºC.
When environmental temperature exceeds 35ºC bird is likely to experience heat stress. In an effect to maintain body temperature birds first rely on losing heat from blood vessels near surface of skin by process called “non-evaporative cooling”.
However, this mechanism is only effective when ambient temperature is lower than bird’s body temperature. As ambient temperature increases beyond bird’s thermo neutral zone, non-evaporative cooling becomes ineffective. At these higher temperatures, birds rely on panting/ evaporative cooling as mechanism for controlling body temperature.
Panting is an effective but energy expensive way for the bird to control body temperature and typically results in lower feed intake and growth as well as reduced feed efficiency between 20-30ºC feed intakes is reduced by 1-1.5% for 1ºC rise in temperature and by 5% above 32ºC.
This will increase water intake to offset water loss but situation is complicated by the fact that body’s ability to retain water is reduced as the evaporative cooling process escalates.
During high ambient temperatures, the birds increase panting up to 10 times from a normal rate of 25 breathes/min to 250 breathes/min. this leads to an excessive loss of carbon dioxide resulting in raised blood plasma bicarbonate levels and increased pH by excreting bicarbonates via urine.
Bicarbonates are negatively charged ions that must be coupled with positively charged ions such as potassium to be excreted in urine.
However, as potassium is important in maintaining intracellular water balance, a loss of potassium ions via urine reduces ability to maintain this water balance.
Consequently, while birds do compensate for water losses associated with panting by consuming more water, its retention in the body cells is limited by simultaneous loss of electrolytes such as potassium in urine.
Effects of Heat on Poultry Birds
Most important effect of heat stress is decrease in body resistance and more susceptibility to E.coli and CRD etc. in summer outbreaks of gout may be seen in broilers and layers.
In heat stressed birds, blood flow increases upper respiratory tract, skin and abdominal muscles for relieving heat, however, blood flow to intestinal tract is decreased. As a result there is reduction in appetite leading to lower feed intake.
Concurrently water intake is increased resulting in fluid contents in intestinal tract. This further cause’s diarrhea that results in loss of electrolytes needed to maintain acid base balance.
Read Also: Vaccination Program for Poultry Chickens
Clinical Signs or Symptoms
the following clinical signs will be observed in heat stressed birds:
- Panting / Rapid respiration
- More intake of water
- Reduced appetite
- Reduction of egg production
- Poor egg shell quality
- Less body weight gain in broilers
- Reduced feed efficiency
- Increase in body temperature
Post Mortem Lesions
- Dehydrated carcass
- Mucoid exudates in mouth and nostrils
- Pale/cyanotic combs
- Pale breast muscles
- Congestion of liver, spleen, kidney and lungs
- Fluid contents in intestines
- Rapid decomposition of carcass.
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