This process is very important in breeders and laying hens, as it affects egg shell quality.
However, it is worth noting that increased panting under heat stress conditions leads to increased carbon dioxide levels and higher blood pH ( i.e., alkalosis), which in turn hampers blood bicarbonate availability for egg shell mineralization and induces increased organic acid availability, also decreasing free calcium levels in the blood. Air sacs are very useful during panting, as they promote air circulation on surfaces contributing to increase gas exchanges with the air, and consequently, the evaporative loss of heat. Birds have an additional mechanism to promote heat exchange between their body and the environment, which are the air sacs. A recent study showed that birds subjected to heat stress conditions spend less time feeding, more time drinking and panting, as well as more time with their wings elevated, less time moving or walking, and more time resting.Īnimals utilize multiple ways for maintaining thermoregulation and homeostasis when subjected to high environmental temperatures, including increasing radiant, convective and evaporative heat loss by vasodilatation and perspiration. In general, different types of birds react similarly to heat stress, expressing some individual variation in intensity and duration of their responses. Under high temperature conditions, birds alter their behavior and physiological homeostasis seeking thermoregulation, thereby decreasing body temperature. Behavioral and Physiological Effects of Heat Stress Therefore, the objective of this review is to compile the current knowledge and evidence available in the scientific (peer-reviewed) literature examining what is known about the importance and impact of heat stress in poultry production, focusing on broilers and laying hens.Ģ. Understanding and controlling environmental conditions is crucial to successful poultry production and welfare. It has been suggested that modern poultry genotypes produce more body heat, due to their greater metabolic activity. However, poultry seems to be particularly sensitive to temperature-associated environmental challenges, especially heat stress. The importance of animal responses to environmental challenges applies to all species. The issue of environmental stress has quickly become a great point of interest in animal agriculture, particularly due to public awareness and concerns. Environmental stressors, such as heat stress, are particularly detrimental to animal agriculture. This imbalance may be caused by variations of a combination of environmental factors (e.g., sunlight, thermal irradiation, and air temperature, humidity and movement), and characteristics of the animal (e.g., species, metabolism rate, and thermoregulatory mechanisms). Heat stress results from a negative balance between the net amount of energy flowing from the animal’s body to its surrounding environment and the amount of heat energy produced by the animal. Therefore, stress represents the reaction of the animal organism ( i.e., a biological response) to stimuli that disturb its normal physiological equilibrium or homeostasis. According to Selye, “stress is the nonspecific response of the body to any demand”, whereas stressor can be defined as “an agent that produces stress at any time”. Stress, a response to adverse stimuli, is difficult to define and understand because of its nebulous perception. This review focuses on the scientific evidence available on the importance and impact of heat stress in poultry production, with emphasis on broilers and laying hens. Nevertheless, effectiveness of most of the interventions has been variable or inconsistent. Intervention strategies to deal with heat stress conditions have been the focus of many published studies. However, our knowledge of basic mechanisms associated to the reported effects, as well as related to poultry behavior and welfare under heat stress conditions is in fact scarce. Much information has been published on the effects of heat stress on productivity and immune response in poultry. Moreover, the negative impact of heat stress on poultry welfare has recently attracted increasing public awareness and concern. The detrimental effects of heat stress on broilers and laying hens range from reduced growth and egg production to decreased poultry and egg quality and safety. Heat stress is one of the most important environmental stressors challenging poultry production worldwide.