Gustavo de Aguiar
Monogastrics Technical Specialist at ICC animal nutrition
Heat stress has become one of the most important environmental constraints in poultry production, particularly in regions where high temperatures and relative humidity occur for long periods of the year. In commercial systems, heat is not only a welfare concern; it is a biological pressure that changes how birds allocate nutrients, energy, and metabolic resources. Poultry are especially vulnerable because their feather cover, absence of sweat glands, and high metabolic rate limit sensible heat loss. When environmental temperature exceeds the bird’s capacity to dissipate body heat, the priority shifts from production to survival. Additionally, in tropical and subtropical markets, this topic deserves even more attention because the thermal challenge often coincides with high humidity, reduced nocturnal cooling, and variable house infrastructure. Under these circumstances, birds may not fully recover during the night, and the next day starts with residual physiological load.
The importance of heat stress is heightened in laying hens because egg formation is a continuous, nutritionally demanding process. A bird must consume enough nutrients to support maintenance, immune function, ovarian activity, shell mineralization, and albumen deposition. Under hot conditions, voluntary feed intake falls as a natural attempt to reduce metabolic heat produced during digestion. Lower intake also reduces the supply of calcium, amino acids, energy, vitamins, and trace minerals required for egg production. Furthermore, the respiratory rate increases, and physiological mechanisms are triggered to maintain internal temperature. Reviews on poultry heat stress describe consistent reductions in productive performance, reproductive efficiency, immune response, and survivability when birds are exposed to acute or chronic thermal challenge (Rostagno and Lara, 2013; Nawab et al., 2018; Vandana et al., 2020; Abdel-Moneim et al., 2021).For egg producers, this shift is critical, as even a short heat wave can reduce laying rate, egg mass, and egg quality, while chronic exposure can compromise persistency, flock uniformity, and profitability.
Why does this happen? The physiological response begins with behavioral and thermoregulatory adjustments. Hens increase panting, spread their wings, reduce activity, increase water intake and seek to enhance heat dissipation through peripheral vasodilation. Panting is essential for evaporative cooling, but it also increases carbon dioxide elimination. This can raise blood pH and trigger respiratory alkalosis, a condition repeatedly associated with reduced bicarbonate availability. In laying hens, bicarbonate is directly involved in eggshell formation, so acid-base imbalance can negatively affect shell mineralization and egg quality. Heat stress also activates neuroendocrine responses, including the hypothalamic-pituitary-adrenal axis, and may alter reproductive hormones. At the cellular level, increased production of reactive oxygen species contributes to oxidative stress, damaging lipids, proteins and membranes. These changes help explain why heat-stressed hens may show lower egg production, reduced egg mass, weaker internal egg quality, and higher susceptibility to health disturbances.
Another important consequence is the impact on gut integrity and immunity. Heat stress can redirect blood flow toward the body surface, reducing intestinal perfusion and impairing epithelial function. When the intestinal barrier is weakened, permeability may increase, and undesirable changes in the microbiota can occur. This creates favorable conditions for opportunistic pathogens and inflammatory responses. Consequently, the immune system then requires more nutrients and energy to maintain defense mechanisms, while the bird is already consuming less feed. This creates a biological conflict: nutrients that would support production are diverted to homeostasis, inflammation control, and tissue repair. Therefore, controlling heat stress is not a secondary management issue; it is central to sustaining output in modern poultry systems. This is why technical monitoring should combine environmental indicators with flock indicators, including behavior, water consumption, feed intake, egg mass, Haugh Unit and signs of intestinal disturbance.
How can nutrition help? Through immunonutrition!
Immunonutrition can be defined as the use of nutrients or functional compounds that interact with immune pathways, intestinal tissues, and microbiota to influence the animal’s response to stressors. In poultry, the gut-associated lymphoid tissue is a major component of immune surveillance, continuously exposed to feed antigens, microbiota, and potential pathogens. Heat stress, dysbiosis, and inflammation are closely connected; therefore, nutritional strategies that help preserve intestinal integrity and modulate immune responses can contribute to better stability. This concept considers nutrition not only as nutrient supply, but also as a way to support immune readiness, gut stability, and resilience under challenge. This does not mean indiscriminately “stimulating” the immune system. A more accurate goal is modulation: preparing innate immune mechanisms to respond efficiently, reducing high inflammatory cost, and helping the bird return to homeostasis after challenge.
In this context, yeast cell wall fractions are among the most studied immunonutritional tools for poultry. Their biological relevance is largely associated with two structural components: beta-glucans and mannan oligosaccharides. Beta-1,3/1,6-glucans can be recognized by innate immune cells, including phagocytes and antigen-presenting cells, located near the intestinal epithelium. This recognition may promote immune alertness and more coordinated cellular responses without requiring tissue invasion by pathogens.MOS, in turn, are related to pathogen agglutination and competitive binding, especially for bacteria that use mannose-sensitive fimbriae, such as some strains of Escherichia coli and Salmonella spp. By reducing pathogen attachment and supporting a more stable microbiota, MOS can indirectly protect intestinal function. During heat stress, when intestinal permeability, oxidative pressure, and inflammatory responses may increase, this type of nutritional support can help the bird maintain a more stable physiological condition and sustain productive performance.
How does it work in practice? Scientific data from ICC Animal Nutrition demonstrate how this nutritional approach can be applied under commercial heat-stress conditions. In a study conducted by Koiyama et al. (2017), commercial white egg-laying hens were exposed to high environmental temperatures, with the thermal challenge exceeding 40°C, and received diets containing different levels ofImmunoWall®,a yeast cell wall-derived product.Under heat stress conditions, hens supplemented with ImmunoWall® maintained a more consistent productive response over time. Cumulative egg production increased from 245 eggs in the control group to 268 eggs in the supplemented group by week 66, indicating better persistency during the challenge period. This response is technically important because, under heat stress, maintaining laying persistency is often more relevant than stimulating short-term egg output. The data suggest that the supplemented birds were better able to sustain production despite the negative effects of high temperature on feed intake, metabolism, and physiological balance. Table 1. Cumulative egg production over time in laying hens supplemented or not with ImmunoWall® under heat stress
| Accumulated egg production (units, by weeks) | Control | ImmunoWall® |
| 22 | 5 | 5 |
| 34 | 73 | 75 |
| 45 | 138 | 145 |
| 50 | 155 | 165 |
| 66 | 245 | 268 |
The same pattern was observed in key productive parameters. Feed intake increased from 93.5 to 96.2 g/bird/day, while egg production improved from 80.7% to 85.4%. Egg mass also increased, from 48.3 to 51.0 g/hen/day. ImmunoWall® helped sustain the number of eggs produced under thermal stress. Internal egg quality was also positively affected. Albumen height increased from 7.67 to 8.02 mm, and Haugh Unit improved from 86.54 to 88.85. These parameters are important indicators of albumen quality and egg freshness, and they are frequently challenged when birds undergo physiological stress. The maintenance of internal quality reinforces that the response was not limited to production volume, but also involved product quality.
Table 2. Productive performance and egg quality parameters of laying hens supplemented or not with ImmunoWall® under heat stress
| Parameter | Control | ImmunoWall® |
| Feed Intake (g/bird/day) | 93,5 | 96,2 |
| Egg Production (%) | 80,7 | 85,4 |
| Egg Weight (g) | 59,9 | 59,8 |
| Egg Mass (g) | 48,3 | 51,0 |
| Albumen height (mm) | 7,67 | 8,02 |
| Yolk color | 4,90 | 4,83 |
| Haugh Unit | 86,54 | 88,85 |
From a technical perspective, these results should be interpreted as support for resilience rather than as complete protection against heat stress. ImmunoWall® does not replace environmental control, ventilation, cooling systems, water management, or adequate diet formulation. However, the data indicate that yeast cell wall supplementation can be a useful nutritional tool to help laying hens cope with thermal challenge.
In commercial egg production, this support is particularly relevant because sustaining performance during heat exposure can directly influence flock persistency and economic outcome. The most consistent benefits were observed in feed intake, laying rate, cumulative egg production, egg mass, and internal egg quality, which are precisely the parameters most sensitive to heat stress. By supporting the gut-immune axis through yeast cell wall components such as beta-glucans and MOS, ImmunoWall® may help birds maintain intestinal stability, immune balance, and productive efficiency during periods of high thermal challenge.
In this approach, nutrition becomes a decisive pillar of thermal resilience. As climatic challenges become more frequent, ImmunoWall® stands out as a practical and scientifically supported nutritional solution to help laying hens sustain productivity, health, and egg quality under heat stress.