Tips about heat stress in layers - Zucami
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Tips about heat stress in layers


With this article, Zucami’s technical team intends to present TIPS to help our customers keep their birds comfortable, within their thermal comfort zone, which will help maintain production levels, egg size and shell quality in an optimal state.

Heat stress in layers has a major impact on bird productivity and mortality, and is one of the most important causes of economic losses for many companies in the poultry laying sector.

The hens have a body temperature around 40-41ºC, which they maintain thanks to their thermoregulation capacity.

In the thermoneutral zone – the temperature range within which birds can lose heat through basic mechanisms such as radiation, convection, and conduction – there is no heat stress and the temperature remains constant.

The proportion of heat lost through radiation, convection and conduction depends on the temperature difference between the bird and the environment.

If the limits of the thermoneutral zone are exceeded, the body temperature rises and the heat stress phenomenon begins. At this point, the bird resorts to evaporative heat loss, a mechanism to fight this situation through panting.

Table 1. Sensible and Latent Heat Loss Methods. Anderson, K. 1997

As the bird’s body temperature increases, feed consumption, growth, feed efficiency, viability and egg shell quality decrease.

As the bird’s body temperature increases, feed consumption, growth, feed efficiency, viability, eggshell quality decrease; this is particularly severe when the ambient temperature rises extremely high, as the possibility of losing heat by non-evaporative means (heat loss through the skin) is significantly reduced.

  Neutral thermal zone. The temperature range in which birds do not need to alter their metabolism to maintain body temperature.

  Ideal temperature range.

  A small reduction in feed intake can be expected, but if nutrient intake is appropriate, production efficiency is good. Egg size may be reduced and shell quality may suffer as the temperature approaches the top of this range.

  Feed consumption is further reduced. Weight gains are lower. Egg size and shell quality deteriorate. Egg production usually suffers. Cooling procedures should be initiated before this temperature range is reached.

  Feed consumption continues to be reduced. There is a danger of heat prostration in layers, especially heavier layers and those in peak production. Cooling procedures should be carried out at these temperatures.

  Heat prostration is likely. Emergency measures may be needed. Egg production and consumption are severely reduced. Water consumption is very high.

  Emergency measures are necessary to cool the hens. Survival is the factor that must matter at these temperatures.


Ambient temperature vs. relative humidity binomial.

The effective temperature is obtained from the combination of temperature and relative humidity of the air. Depending on the conjugation of these parameters, the heat stress situation can be reached. Increased air humidity at any temperature will increase bird discomfort and heat stress.

Producers should carefully monitor temperature and humidity in their installations. 

Main signs of birds affected by heat stress.

In the beginning, the most frequent thing is that the birds, when trying to recover their thermal balance, modify their behavior, which can be observed:

Birds with distended wings.

Squatting on the ground.

Slowness, lethargy.

Stupor, staggering, terminal convulsions

Wet feces.

Increased water consumption.

Decrease in feed consumption.

They start with slow gasps and end up panting very quickly.

Detour of blood from the internal organs to the skin, which darkens the color of the skin.

Terminal convulsions.

Increased mortality.

  Shell quality and heat stress.

Layers affected by heat stress lay eggs with very thin shells due to the acid-base imbalance in the blood which results in them starting to pant.

When birds hyperventilate to lose body heat, there is an excessive loss of CO2 gas in the lungs and blood. The decrease of CO2 gas in the blood causes the blood pH to rise or become more alkaline. This condition is known as respiratory alkalosis.

The increase in the pH of the blood reduces the activity of the enzyme carbonic anhydrase, resulting in reduced calcium and carbonate ions transferred from the blood to the shell gland (uterus). Increasing calcium in the diet will not correct this problem.

Another factor that also contributes to thin eggshells is the decrease in calcium intake as feed intake decreases, and the increase in phosphorus loss.

  Measures to prevent heat stress in birds.

The effects of heat stress can be minimized by applying a comprehensive plan, the strategy should include a complete biosecurity plan, a plan for ventilation management and water management in terms of quality and temperature, and finally an adequate feeding and nutrition plan.

All these measures are more effective from the point of view of prevention, since controlling heat stress problems once they have been triggered is very complicated and the economic losses can have a great impact on the farm.

In today’s poultry production, heat stress is a very important problem that leads to great economic losses. Therefore, efforts must be made to prevent environmental conditions from causing these heat stress situations, and management and nutritional measures, or combinations of both, must be implemented.