QUESTIONS, ANSWERS, and TIPS ON HEAT STRESS
Heat stress occurs whenever the animal is exposed to a temperature above its “thermoneutral zone”
We can define the “thermoneutral zone” as the range of temperatures within which the animal does not exhibit the characteristic symptoms of heat stress because it is still able to maintain its body temperature consistently, showing normal behavior.
The thermoneutral zone for laying hens ranges between 19 and 22°C, while for broilers it ranges between 18 and 22°C.
What are the symptoms of heat stress?
In general, poultry exhibit similar behaviors in response to heat stress, with variations in intensity and duration of the response.
Animals affected by heat stress:
- Spend less time feeding
- Increase their drinking rate
- They breathe with their beaks open
- They lift their wings
- They are more lethargic
Why do they exhibit these symptoms?
The high metabolic activity of the animal for growth or egg production results in high heat production.
This heat production depends on several factors, including: breed, body weight, level of production, feed intake, type of feed, and exercise.
Dissipating this heat in poultry is not simple, as unlike mammals, they do not have sweat glands.
When external temperatures exceed the animal’s thermoneutral zone, the mechanisms used for heat dispersion become less effective, and the consequences can be detrimental.
How do poultry dissipate heat?
Heat dissipation in poultry species can occur through five main mechanisms:
- Conduction:
This occurs through heat dissipation via contact between the animal and a surface, such as bedding or a wall.
- Convection:
Convection involves heat dissipation similar to conduction but through a moving medium, such as forced air flow.
This is the most efficient method for dissipating heat, provided the airflow over the animal is fast enough to remove the layer of air around the animal where conduction occurs.
To support this heat dissipation method, modern farming technologies utilize forced ventilation systems, often with air cooled by systems like cooling systems.
- Radiation:
This involves the radiation of heat into the surrounding environment through electromagnetic waves.
This type of heat dissipation does not require a medium like air to occur.
To optimize these processes, the animal often slightly spreads its wings to facilitate greater heat exchange with the air and surrounding elements.
- Evaporation:
Evaporation is extremely important because poultry lack sweat glands. It occurs through the skin or open-beak breathing. In particular, the nasal cavities are the most efficient means for evaporation, which is why open-beak breathing is one of the first symptoms of heat stress. However, evaporation is only effective if the humidity is not excessively high; thus, a warm and humid environment is much more stressful than a warm and dry one.
- Excretion:
Another way to dissipate heat is through increased liquid excretion via urine and liquid feces.
What are the effects of heat stress?
The effects of heat stress depend on the duration and frequency of the animal’s exposure to the stressor.
Exposure to high temperatures can indeed be either acute and sudden or chronic, as during summer cycles when the animal is exposed to temperatures significantly above the thermoneutral zone for extended periods.
Chronic exposure does not exclude acute exposure and vice versa; however, while acute exposure is often associated with increased mortality, frequently due to suffocation, chronic exposure is associated with reduced performance due to the effects of oxidative stress on the animal.
What are the effects of oxidative stress and how does it occur?
One of the responses to heat stress that we have seen is to dissipate heat through exchange with the surrounding environment.
To achieve this, the animal’s physiological response is to increase peripheral blood flow by dilating the blood vessels in superficial tissues such as the skin, at the expense of visceral tissues, thus reducing blood flow to internal organs such as the intestines.
The resulting hypoxia generates a quantity of reactive oxygen species (ROS), commonly known as free radicals, that exceeds the animal’s capacity for elimination.
What results is what is technically referred to as oxidative stress, and the direct consequence of this state is cellular damage, with loss of structural integrity of the intestine, a local inflammatory response, and altered immune response.
Along with the alteration of the intestinal barrier, negative changes in the gut microbiota (the population of microorganisms that inhabit the intestine and are essential for maintaining certain intestinal functions) also occur.
The combination of these alterations creates a syndrome known as “leaky gut syndrome”, literally translated as “leaky gut syndrome.”
This syndrome is described as a disruption of the structural integrity of the intestine and directly results in excessive loss of fluids, which inevitably leads to poor food assimilation, reduced feed efficiency, decreased conversion, and overall performance.
Is it possible to counteract oxidative stress damage?
The main tool available to the farmer is to prevent oxidative stress from occurring by avoiding heat stress.
Below are some tips for the farmer that can be useful for reducing endogenous heat production in the animal and promoting heat dissipation.
- Avoid ad libitum feeding and provide high-quality feed only during the cooler hours
- Ration the feed, meaning calculate the amount of feed necessary for the animal to maintain physiological functions and performance without exceeding the quantity per head per day.
- Always provide fresh and clean water because if the water heats up, the resulting environment promotes bacterial growth.
- In intensive farming, adjust the ventilation based on heat stress symptoms and, if necessary, make use of cooling systems like cooling systems or misting systems.
- In outdoor farming, create shaded areas if trees are not present.
From a nutritional standpoint, the farmer can intervene by supplementing drinking water with minerals and electrolytes, which are lost when leaky gut syndrome occurs.
Another intervention that can be implemented is to supplement the diet with antioxidant substances from plants and derivatives, along with vitamin C which work synergistically to counteract the negative effects of free radicals produced during oxidative stress, which, as we have seen, is the direct consequence of heat stress.
In this regard, Tecnozoo recommends NORMOTERM FLUID, which helps counter oxidative imbalance thanks to its natural antioxidant substances, maintaining the animal’s physiological balance, especially in stressful situations.
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