Temperature is a stressor that affects global poultry production and has a significant impact on welfare and production. The digestive tract is very sensitive to any stress and the effects of heat stress on gut health and function are often underestimated.
by MVDr. Zuzana Machovcová, Ph.D., MVDr. Renata Kučerová
ADDICOO GROUP, Czech Republic (www.addicoo.com)
Published: Náš chov, Volume LXXXIII, Number 6 (2023)
Heat stress
Stress is a biological adaptive response to abnormal conditions (stressors) with the purpose to restore homeostasis and prevent damage to the organism. The autonomic nervous system is activated during heat stress at the beginning of the hyperthermic period. In poultry, it leads to increased respiration frequency and heart rate, reduced nutrient flow from the GIT accompanied by impaired energy and calcium metabolism. The consequence is a reduced ability to adapt to heat stress. When tolerance thresholds are exceeded, damage to the organism occurs.
Impact of heat stress on intestinal integrity
The permeability of the intestinal wall is directly affected by the increased concentration of stress hormones due to higher temperatures. Heat stress causes hypoxia and reduces blood flow in the intestinal wall. There is a reduced availability of oxygen and nutrients to the intestinal mucosa, decreased height of the villi, a reduction in the ratio of the length of the intestinal villi to the depth of the intestinal crypts, and smaller numbers of lactobacilli and bifidobacteria. Oxidative stress and inflammation occur, which is manifested by damage to the cells of the intestinal mucosa and disruption of the integrity of the intestine. Another manifestation of oxidative stress is a decrease in the expression of tight-junction proteins, which are responsible for the formation of tight junctions between intestinal epithelial cells. This results in increased permeability of the intestinal wall and the passage of pathogens, endotoxins and metabolites from the gastrointestinal tract into the systemic bloodstream. Increased endotoxin load on internal organs due to penetrating bacteria may limit anabolic processes in the body, and if the load is severe, it can lead to multi-organ failure. Therefore, a functional gastrointestinal tract is essential for overall animal health and performance.
Oxidative stress
Oxidative stress can be described as the presence of reactive oxygen species (ROS) exceeding the available antioxidant capacity of animal cells. In the initial phase of acute heat stress, mitochondrial substrate oxidation and electron transport chain activity increase, leading to excessive production of reactive oxygen species and depletion of antioxidant stores. One of the main antioxidants is glutathione, which plays an important role in detoxification reactions by protecting cells from the harmful effects of ROS. These substances are produced intracellularly and in case they are present in excessive amount, cell damage could occur without further intervention. Antioxidant enzymes (superoxide dismutase, glutathione peroxidase, catalase) are an integral part of the adaptive mechanism to various stress conditions. The synthesis of these enzymes during periods of heat stress helps to reduce reactive oxygen species and acts as a prevention of oxidative stress.
Fortibac® X-Energy and its effect on heat stress
Animals in heat stress limit heat production by reducing feed intake, resulting in poorer performance – reduced daily gains, higher feed conversion, poorer meat and egg quality and decreased egg production. Short and medium chain fatty acid esters, which are the basis of the entire Fortibac® product line, have been shown to be beneficial at times of heat stress in poultry. Their beneficial effect consists in optimising the morphology of the intestinal wall, reducing presence of pathogens, promoting a beneficial microbiome, modulating the intestinal immune system, anti-inflammatory action and improving the antioxidant parameters of the organism.
A total of 342 ROSS 308 broilers divided into two groups (experimental and control) were participating in the trial. Both groups were fed a standard feed mixture according to the ROSS 308 manual and the length of the fattening period was 35 days. The feed ration in the experimental group was supplemented with the additive Fortibac® X-Energy, based on fatty acid esters supplemented with an emulsifier and phytogenic substances. The broilers were exposed to heat stress continuously from day 14 of the experiment 10 hours per day at a temperature of 33±1 °C. The results of the performance parameters are presented in the table. The experimental group of broilers showed better performance parameters compared to the control group: feed conversion improved by 2.1%, daily gain increased by 2.9%, final weight increased by 2.3% and fattening efficiency index (EPEF) improved by 13 points.
| Group | FCR | Average intake (g/broiler/day) | Average daily gain (g/broiler/day) | Average final weight (g) | Mortality (%) | EPEF (points) |
| Control | 1.55 | 90.0 | 58.2 | 2 142 | 1.2 | 391 |
| Fortibac® X-Energy | 1.51 | 90.7 | 59.9 | 2 191 | 2.3 | 404 |
| Difference vs control | -0.04 | +0.7 | +1.7 | +49 | +1.1 | +13 |
Table: Comparison of broiler performance parameters.
In the evaluation of antioxidant capacity, the experimental group showed better results, with a 6.8% increase in catalase activity compared to the control group (Figure 1). The experimental group manifested higher levels of reduced glutathione (GSH) by 41.5% (Figure 2) and reduced levels of oxidized glutathione (GSSG) by 18.4% (Figure 3). The GSH/GSSG ratio in cells is often used as an indicator of the antioxidant capacity of a cell. In the case of the Fortibac® X-Energy group, the GSH/GSSG ratio was 124.5% higher than in the control group (Figure 4).
Activity of the antioxidant enzyme catalase Levels of reduced form of glutathione (GSH)
Levels of oxidized form of glutathione (GSSG) Ratio of reduced and oxidized glutathione
Conclusions
The above results show that Fortibac® additives, based on an optimal combination of fatty acid esters, can reduce the effects of heat stress on poultry in terms of better performance and improvement of the antioxidant parameters of the organism. The products offer farmers an effective solution for more profitable farm economics and increased production quality not only during periods of heat stress.