ISSUE FOCUS 62 FEED & ADDITIVE MAGAZINE July 2025 num, shorter villi (Figure 4), and reduced absorption areas, in comparison to non-stressed animals.11, 12, 23-26 Changes in intestinal microbiome Due to reduced feed intake and impaired intestinal function, the presence and activity of the commensal microbiota can also be modified. Heat stress can lead to reduced populations of beneficial microbes. At the same time, it can boost the growth of potential pathogens and lead to dysbiosis, increased gut permeability, as well as immune and metabolic dysfunction.27 Burkholder et al. (2008) and Rostagno (2020) point out that pathogens such as Clostridia, Salmonella, and coliform bacteria increase in poultry exposed to heat stress, while the populations of beneficial bacteria such as Lactobacilli and Bifidobacteria decrease. Necrotic enteritis Heat stress in poultry causes damage in the gut microbiota, intestinal integrity, and villus morphology, as well as immunosuppression. Consequently, feed digestion and absorption decline.11, 12, 28, 29 These factors increase the risk of necrotic enteritis outbreaks5, 28, 30, 31, one of the most problematic bacterial diseases in modern poultry production. In a study by Tsiouris et al. (2018), cyclical acute heat stress was found to increase the incidence and severity of necrotic enteritis in broilers challenged with C. perfringens, and to produce the disease in animals that were not exposed to the bacteria. Other signs, such as growth retardation and a reduced pH of the intestinal digesta, were also observed in the heat-stressed birds. By lowering feed digestibility, increasing gut permeability, and compromising immunity, heat stress leaves animals more susceptible to gut-health related issues such as dysbacteriosis and necrotic enteritis – and thus increases the need to use antibiotics. 160% 140% 120% 100% 80% 60% 40% 20% 0% Dudenum morphology (villous height and width as % of the control group) in heat-stressed broilers Height Width Control Figure 4. Villous height and width of broilers exposed to heat stress in relation to the control group (100%). Villous height is always shorter than the control group, but width can increase when the organism shows resilience to the stressful situations and aims to recover intestinal surface. (Adapted from Jahejo et al., 2016; Santos et al., 2019; Wu et al., 2018; Abdelqader et al., 2016; Santos et al., 2015 and Awad et al., 2018 – by order of appearance in the graph, from left to right)
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