How endotoxins aggravate heat stress in broilers

Higher ambient temperatures in poultry housing have an influence on birds’ behavior, physiology and immune system, making them more susceptible to endotoxins with negative consequences on welfare and performance. Heat stress costs the U.S. poultry industry alone it thought to cost approximately US$128-165 million each year.

Heat stress impairs gut barrier function

In a healthy bird, tight junction proteins seal the spaces between intestinal epithelial cells, ensuring an intact gut barrier that helps to prevent pathogens or toxins from entering the blood stream (Figure 1a). However, during heat stress, tight junction proteins can be disrupted (Figure 1b) which allows pathogens or toxins to enter the circulatory system.

An impaired gut barrier due to different stress events

Heat stress increases a bird’s gut permeability by two-fold, work conducted at the BIOMIN Research Center confirms.

Twenty-eight day old birds were either kept at thermoneutral conditions (23°C) or at heat stress conditions (36°C) for 10 hours. A marker molecule (FITC-Dextran) was administered orally and later measured in the blood to assess gut permeability. The gut permeability of the heat stressed animals doubled compared to that of birds in thermoneutral conditions.

Endotoxins harm broilers and laying hens

Endotoxins, also known as lipopolysaccharides (LPS), are part of the outer membrane of the cell wall of Gram-negative bacteria (e.g. E. coli, Salmonella). LPS are released from bacterial cell walls by shedding or through bacterial lysis. There are many natural sources of endotoxins including air, dust, food, water, and feces, but the major source is the gastrointestinal tract.

Poultry are exposed to LPS throughout their lives. In healthy birds, the intestinal and other epitheliums such as skin or lungs, represent an effective barrier that prevents the passage of LPS into the bloodstream. Once there, however, endotoxins can elicit strong immune responses, weakening birds’ immune systems and impairing performance. Severely pronounced immune response can lead to septic shock.

LPS raise intestinal immune response during heat stress

A study was conducted at the BIOMIN Research Center to assess the influence of endotoxins on inflammation response of the intestine in heat-stressed birds.

The combination of heat stress and LPS led to an increase of the expression of various genes related to heat stress and inflammation (Table 1). The expression of heat shock protein (HSP70) was increased up to 90-fold when the oral dose of LPS was applied. In addition, the cytokines interleukin 1beta and interleukin 6 –all indicative of inflammatory processes— showed a more prominent effect when both stressors were present.

Heat shock protein↑↑↑↑↑↑↑↑
Interleukin 1beta↑↑
Interleukin 6↑↑↑↑↑↑

< 5 fold increase
> 5 fold increase
> 50-fold increase
*Red indicates a significant increase compared to the negative control

Need for endotoxin control

The presence of endotoxins can cause birds to waste energy on activation of the immune system, leaving less energy available for growth and performance. This underscores the importance of proper endotoxin risk management. Table 2 highlights several ways to reduce the impact of heat stress and endotoxin contamination. When combined with good farm practice and the reduction of other stressors such as heat stress or mycotoxin contamination, the threat of endotoxins on bird performance can be eliminated.

EndotoxinsCorrective action
Adapt diet to birds' needs according to production status (e.g. switch to corn-based diet instead of rye-wheat-barley diet
Implement stress reduction measures (e.g. temperature control, welfare enhancement)
Verify hygiene management e.g. reduce dust, ensure proper and regular cleaning of barns
Enhance liver support and strengthen gut permeability through feed additives that provide bioprotection
Apply a mycotoxin binder with demonstrated ability to capture endotoxins
Reduce or eliminate the subtherapeutic use of antibiotics


Heat stressProvide adequate ventilation for number of birds housed
Reduce stocking densities
Insulate sheds sufficiently to avoid solar heat gain
Position fans to optimize wind speed an air circulation
Use evaporative cooling pads or atomizing nozzle
Maintain water-electrolyte balance
Vitamin supplementation
Apply a phytogenic feed additive to reduce the effects of heat stress

This article originally appeared in Poultry International.