Physiology of heat stress in birds
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Written by Franklin Gutiérrez

Published August 23, 2020

Birds, being homeothermal animals have a thermoregulatory center located in the hypothalamus capable of controlling body temperature through physiological mechanisms and behavioral responses, by producing and releasing heat thus determining the maintenance of normal body temperature.

Among the compensatory physiological responses of birds when exposed to heat is peripheral vasodilation, resulting in non-evaporative heat loss. Thus, in an attempt to increase heat dissipation, the bird manages to increase the surface area by opening the wings, bizarening the feathers and intensifying peripheral circulation. Non-evaporative heat loss can also occur with an increase in urine production, if this loss is offset by increased cold water supply.

Another physiological response is increased breathing rate, resulting in excessive loss of carbon dioxide (CO2). Partial CO2 pressure decreases, leading to drop in carbonic acid (H2CO3) and hydrogen (H+) concentration. In response, the kidneys increase HCO3 excretion and reduce H+ excretion in an attempt to maintain the bird's base acid balance. This change is called respiratory alkalosis.

In considering all the aspects raised in relation to the issue of poultry production in warm climates, it was found that some conditions are not suitable for the rearing of birds in areas with high temperatures and as a solution the improvement of environmental conditions within the facilities such as the use of refrigeration systems, together with some nutritional management practices and ration was implemented.

Broiler chicken is a genetically enhanced pet towards rapid growth and the already known high yield. During the selection process the metabolism of birds was even faster with advances in genetics and nutrition focused on rapid growth, with maximum protein deposition, especially in breast and thigh, better use of nutrients in the diet and good food conversion. However, thermoregulation capacity remained poor in addressing the main challenges of high temperatures.

Most modern chicken lineages are known to be genetically enhanced to meet the demands of countries located in temperate areas. The expansion of the trade scale of these lineages to tropical and semitropical countries caused nutritional needs to be reassessed in order to allow them to express their maximum performance at high ambient temperatures.

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