Chicken heat stress: Nutritional tips for broilers and layers

With ambient temperature records being broken every year and heat waves becoming more frequent, broiler and layer farms are being exposed to an ever-greater duration and intensity of heat stress.

Heat stress can affect several bodily systems. For instance, as blood flow is redirected to the skin in an effort to lower body temperature, less is available to sustain the internal organs. This breaks down the bird’s intestinal barrier, causing a “leaky gut” that impairs digestive efficiency and allows pathogenic bacteria to reach internal organs.

Figure 1: Intestinal integrity breakdown due to heat stress. Source: Lian et al. (2020).

Oxidative stress is another prominent feature of heat stress in poultry. Heat stress triggers the massive production of “free radicals” (reactive oxygen species, or ROS), thereby overwhelming the capacity of a bird’s antioxidant defense system, including antioxidant enzymes such as glutathione peroxidase (GPx) and superoxide dismutase (SOD). This leads to the accumulation of ROS, which damages vital components of cells, such as lipids, proteins and genetic material.

Figure 2: Heat stress is a major cause of oxidative stress. Source: Wasti et al. (2020)

The health of broilers and layers, as well as the quality of poultry meat and eggs, can be seriously compromised by the oxidative stress induced by hot weather, as explained in the figures: 

Figure 3: Broiler meat yield and quality are impacted by heat stress. Source: Fouad et al. (2016).

Figure 4: Eggshell strength and internal egg quality are seriously affected by heat stress. Source: Fouad et al. (2016).

Mannan-rich fraction (MRF)

The gut (intestinal) microbiome is the collection of microbes that reside in the gut. It includes many different species of bacteria, fungi, viruses and other organisms. The diversity of the gut microbiome is one of the most critical determinants of gut health. Indeed, a diverse and balanced gut microbiome can reduce the load of pathogenic bacteria (Salmonella spp., Campylobacter jejuni, E. coli, Clostridium perfringens, etc.) through a process called competitive exclusion, in which bacterial species compete with one another for the available nutrients and adhesion sites to the gut wall.

Figure 5: Key layers of the intestinal (gut) barrier. Commensal bacteria have a crucial role in preserving this barrier, due to their ability to compete with, and thus limit colonization by, pathogenic bacteria. Source: Sharma and Riva (2020).

Heat stress causes dysbiosis, which is a perturbation of the gut microbiome. Dysbiosis leads to an overgrowth of pathogenic bacteria.

Another harmful consequence of dysbiosis is the disruption of the gut barrier and intestinal hyperpermeability (“leaky gut”), allowing for the translocation of bacteria and endotoxins, which will induce systemic inflammation. Indeed, the disruption of the gut barrier is considered the starting point of the negative consequences of heat stress on animal productivity, welfare and health.

Figure 6: At high ambient temperatures, gut dysbiosis leads to an overgrowth of opportunistic pathogens, weakening of the gut barrier and hyperpermeability of the gut (“leaky gut”). As a consequence, intact bacteria and bacterial components, such as lipopolysaccharide (LPS), translocate into the portal vein and cause hepatic inflammation, followed by endotoxemia and systemic inflammation. The elevated levels of proinflammatory cytokines and LPS are associated with a decrease in feed intake, typical of animals under heat stress, as well as a decrease in lean carcass growth. Source: Ringreis and Eder (2022).

Alltech’s proprietary mannan-rich fraction (MRF) is a unique, second-generation, bioactive fraction derived from a select strain of Saccharomyces cerevisiae. MRF has been shown to have a consistent effect on gut microbiota, promoting bacterial diversity and helping to support the resistance to colonization with pathogens such as Salmonella and Campylobacter.

For some pathogenic bacteria, including E. coli and Salmonella spp., to colonize the gut, they must first attach to mannose receptors on the gut wall via type 1 fimbriae. MRF has been shown to adhere to (agglutinate) these type 1 fimbriated bacteria, preventing them from attaching to the gut wall.

Figure 7: MRF adsorbs (agglutinates) pathogenic bacteria in the gut (intestine). Source: Alltech.

Optimal trace mineral nutrition: Bioplex® and Sel-Plex®

Bioplex® are metal proteinate chelates that are bound to a range of peptides. Bioplex trace minerals (zinc, manganese, copper and iron) are easily absorbed and readily metabolized, supporting animal performance and efficiency — especially when feed intake is compromised due to heat stress.

Sel-Plex® is Alltech’s proprietary organic form of selenium yeast.

It is widely documented that Bioplex and Sel-Plex optimize the activity of antioxidant enzymes and, thereby, aid with oxidative stress. This is particularly important to optimize eggshell quality in long production cycles.

In recent years, European egg producers have witnessed the significant benefits of Alltech’s eggshell quality program. The collection and analysis of data from numerous flocks, across several European countries, corresponding to 14 different laying hen breeds and all housing systems, showed a clear improvement in eggshell strength:  

Figure 8: Average eggshell strength (by age range) of laying hen flocks, Alltech eggshell quality program, compared to inorganic trace minerals (ITM). Source: Alltech.

In conclusion, Alltech solutions such as MRF and highly bioavailable trace minerals are ideal to support poultry health and performance during hot weather. The equilibrium of bacterial populations in the intestine is restored by MRF, thus supporting gut wall integrity and nutrient digestion and absorption. The potent antioxidant effects of Bioplex and Sel-Plex support the gut and internal organs against oxidative damage, optimizing poultry meat and egg quality in flocks under heat stress.

* References are available upon request.

About the author:

Joel Estevinho is the European poultry technical manager at Alltech. In this role, he offers technical support to Alltech's poultry clients in Europe. His areas of focus include cage-free production, bird health and welfare, eggshell quality, sustainable poultry production and reduction of antibiotic use.

After obtaining his veterinary medicine diploma in 2005 in Portugal, Joel acquired vast experience in breeder and laying hen management, in all types of production systems. He has also held several positions in sales and quality management of poultry products in Europe and South America, having worked closely with poultry companies in over 10 countries. 

Joel joined Alltech in 2020. Before joining Alltech, he worked at a major primary breeding company for eight years.

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