Laying hens can be greatly affected by heat stress, so it is important to know its impact and how to prevent it.

The poultry industry has been developing rapidly during the last decades. This development has been favored by improvements in the genetic selection of the different strains of laying hens. There have also been remarkable improvements in nutrition, intestinal welfare, and management. The combination of all these processes and their optimization have allowed poultry farming to respond to the important demand for feed worldwide.

Heat stress: importance in poultry farming

Production poultry has increased the speed at which they develop during their juvenile stage and the production stage. The increase in their metabolic rate to achieve rapid development and more efficient productive stage has generated changes in the physiology of this poultry.

However, a fast metabolism means that nutrients are rapidly consumed and transformed. These biochemical processes generate heat that the poultry are unable to dissipate properly.

The poultry can lose heat by several routes that are not always efficient: first, by radiation, where the body emits heat to the environment, but the feather covering limits this. Secondly, by conduction by encountering cold surfaces, but caged laying poultry does not have this method of removing heat properly. Thirdly, by convection by transferring heat to the circulating air, which depends on an efficient ventilation system in the house. Lastly, evaporation through respiration, but depends on the ambient humidity to be efficient. For these reasons, poultry is susceptible to heat stress, which is contrary to animal welfare.

It is estimated that in the United States, heat stress generates economic losses of millions of dollars in poultry farming, with about USD 128-165 million annually. In this same country, heat stress generates a 0.5% to 7.2% decrease in egg production, which generates important annual economic losses.

Impact of heat stress on laying hens.

Heat stress affecting production poultry can be divided mainly into two types according to their severity and duration: acute and chronic. Acute heat stress is characterized by drastic heat exposure in a short time, generating acute signs in the poultry. On the other hand, chronic heat stress is described as a prolonged and sustained state in time that has a variable severity in terms of the heat that affects the poultry.

This poultry problem has impacts in several ways, related to poultry functionality and physiology as described below.

Productive performance and nutrition

Research in poultry farming has found that heat stress in laying hens causes loss in body weight, lower egg production, lower egg weight, and affect eggshell quality.

In addition, poultry under heat stress decreases their feed intake. It has been found that chronic heat stress significantly reduces dietary protein intake and affects feed digestibility, especially of lipids and proteins. As a result, the productive performance and health of the poultry are compromised.

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Mineral balance

Laying hens are animals that require a correct mineral balance to ensure the laying stage, especially minerals such as calcium. However, during acute heat stress, it is observed that the acid-base balance is altered, which interferes with calcium absorption at the duodenal level. Heat increases the respiratory rate of the poultry, which eliminates a large amount of CO2, leading to respiratory alkalosis. It has been reported that in this state the available ionic calcium in plasma, that allows the formation of the eggshell, is reduced, affecting its quality and thickness; in addition, this ionic imbalance predisposes to the deterioration of the skeletal system.

Immune system

Research on heat stress in poultry farming shows that it has an impact on the immune system. It has been found that this problem affects specific immunity in young poultry, causing suppression of white blood cells and an increase in the heterophile/lymphocyte ratio (stress indicator).

In addition, heat stress in laying hens has been studied to reduce the number of antibodies produced in chickens under certain conditions. This reduced immunity predisposes production poultry to suffer high morbidity and mortality in cases of infectious diseases. It can even affect the vaccination process since effective immunization is not achieved.

Mortality

Studies of heat stress in the poultry show that this pathology significantly increases the percentage of mortality due to suffocation of the poultry in acute cases and immunosuppression in chronic cases.

Reproductive physiology

The reproductive system of the poultry is the system in charge of egg formation. Heat stress affects its functionality since it causes oxidative stress in the ovarian follicles. On the other hand, it has been found to increase molecules that induce apoptosis in liver cells, with similar severity to mycotoxins.

Control strategies against heat stress

Poultry houses are characterized by a high density of animals in the facility. This high number of animals increases the heat inside the house if proper management conditions are not set. However, there are strategies on several fronts to control heat stress in poultry.

Curtain management

Poultry houses can improve temperature and humidity conditions through curtain management. In this way, outside air cools the inside of the poultry house and reduces heat. On the other hand, temperature and humidity meters should be available to make a correct balance of these parameters. A controlled and comfortable environment for poultry improves animal welfare and production.

Ventilation systems

Large or high-density poultry houses should have an efficient ventilation system that guarantees a controlled environment. In addition, they reduce the incidence of problems related to humidity, ammonia, and heat stress. It is recommended to periodically check the efficiency of fans and exhaust fans to always ensure their operation.

Water and feed

Water available for consumption can increase in temperature if the poultry house is accumulating heat. This seriously affects the condition of the poultry as it reduces their water consumption and increases stress. Therefore, the water temperature should be constantly monitored concerning the ambient temperature and should be cool.

On the other hand, the feed ratio in tropical countries or areas with high ambient temperatures can be adjusted. The amount of protein, carbohydrates, and lipids included in the diet can be adjusted to reduce the metabolic rate of the poultry and avoid a state of heat stress.

Mineral and vitamin supplementation

Poultry can be supplied with mineral and vitamin supplements, such as Alquerfeed Ovoponedoras, which contributes positively to the quality of the eggshell. This product optimizes egg formation especially in conditions of heat stress in laying hens. Thanks to this, it prevents bone demineralization and improves calcium levels available for optimal physiology.

Immunostimulants

The immunostimulants supplied in the diet allow strengthening the poultry’s immune system, avoiding immunosuppression states caused by heat stress. Alquernat Inmuplus strengthens the specific and non-specific immune system of poultry, both in young and adult animals. Thanks to this, the response to vaccination is enhanced and contributes to improving the health status of the poultry house against infectious diseases.

CONCLUSIONS

Laying hens have been genetically selected to increase their productive performance and efficiency. In addition, remarkable advances in nutrition and welfare have been applied to contribute to their production.

However, poultry physiology presents drawbacks to controlling excess heat. Poultry is characterized by a high metabolic rate and heat production that they are unable to dissipate. Therefore, heat stress occurs in poultry farming.

Heat stress generates different pathological effects in poultry, including a lower productive performance in laying hens which affects egg quality. In addition, feed intake is reduced, and the mineral balance is altered. The immune system is affected, as well as the physiology of the reproductive system.

There are several ways to face heat stress in poultry, which include correct management of curtains, the adaptation of ventilation systems, and revision of the water and feed supplied. Finally, some products provide vitamins and minerals to avoid heat stress, as well as immunostimulants that strengthen the poultry’s immune system.