Effects Of Heat Stress on Broilers.

Global warming is producing great changes in the performance of broilers due to heat stress, because stress produces alterations in different organs and systems of animals and humans.

The main effects of heat stress on chickens are:

1.      Microbiota. There are changes in the composition of the gut microbiota of chickens, in which the populations of pathogenic bacteria such as Salmonella, Escherichia coli, and Clostridium are increased, but the populations of beneficial microorganisms such as Lactobacillus and Bifidobacterium are reduced.  As a result of the imbalance of the microbiota, there is diarrhea; but in addition, E. coli can pass from the intestine to internal organs, affecting the heart and lungs, for example. (Wen et al., 2021)

2.      Immunity. Heat stress alters the balance relationship between the host (the chicken) and its beneficial microorganisms, making the intestine susceptible to infections from pathogenic organisms.

Acute heat stress decreases T helper cells (T-helper lymphocytes) and increases the number of NK cells, which can weaken the immune response, since NK cells do not replace the coordinating function of T helpers in adaptive defense, especially against bacterial infections. Heat stress can induce inflammatory responses and cause damage to the tissues of the intestine by increasing the permeability of intestinal cells and producing inflammation of the muscle. (Wen et al., 2021) 

3.      Intestine. Heat stress causes damage to the digestion and absorption of nutrients. Reduces the activity of proteolytic enzymes and pancreatic lipase. The proteins of the tight junctions between the cells of the intestine are also altered, and as a consequence, the passage of bacteria and toxins to the circulation via the portal is opened. Heat stress produces free radicals, which results in the death of cells in the gut. (Wen et al., 2021) 

4.      Other viscera. Acute heat stress causes inflammation and cell death mainly of the lung, but it also affects the heart and liver, resulting in increased mortality. (Nan et al., 2023)

5.      Zootechnical performance. When animals are under heat stress, feed intake is reduced, weight gain is decreased, feed conversion (feed intake/weight) is increased, mortality is increased, and water consumption is increased. (Rocchi et al., 2022)

Because of what is contained in numbers 1 to 5, it is necessary to avoid chickens and farm animals in general, from being under stress conditions caused by high temperatures. By avoiding heat stress, all production parameters are significantly improved.

Expect information on nutritional alternatives to reduce the effects of heat stress in the next newsletter.

GABRIEL DIAZ, PhD.

Referencias:

1.      Jiuhong Nan, y otros. Transcriptome analysis of multiple tissues reveals the potential mechanism of death under acute heat stress in chicken. BMC Genomics, 2023, 24:459.

2.      Alessandro Rocchi y otros. Experimental cyclic heat stress on intestinal permeability, bone mineralization, Leukocyte proportions, and meat quality in broiler chickens. Animals, 2022, 12, 1273.

3.       Chaoyue Wen y otros. Microbiota-gut-brain axis and nutritional strategy under heat stress. 2021. 7: 1329-1336.