by Manu de Laet, CTS, Delacon Biotechnik GmbH

The demand for poultry meat is increasing globally as a result of increasing population and popularity. Poultry meat is a very economical source of high-quality protein that is accessible in most regions across the globe. The predominant areas of increased demand, however, are in (sub)tropical regions where not only high temperatures but, also, high humidity levels have negative impacts on the efficiency of poultry production.

The genetic factors that have been selected for growth and metabolic efficiency in broilers make them susceptible to heat stress. Faster growing breeds are more sensitive than slower growing breeds, males are more prone to reduced performance than females, and the negative effects of heat stress are increased with age.

Heat and humidity reduce performance

Heat stress is characterised as an imbalance between heat production and heat loss. Birds are unable to maintain thermoneutrality due to the environmental impact of both heat and humidity. The duration of heat stress (acute versus chronic,) the nature of heat stress (cyclic versus constant), and temperature-humidity index (THI) determine the severity of the effect on production performance.

Physiologic thermoregulation mechanisms, both to reduce heat production and to expedite heat loss, can lead to reduced production efficiency and increased mortality. Decreased activity and feed intake can lead to nutrient deficiencies and panting which can lead to respiratory alkalosis and acid/base imbalance.

In addition, increased oxidative damage, inflammation, reduced gut integrity, and an increase of stress hormone production negatively impact production efficiency as well as the quality of the final products, meat and eggs.

Phytogenics can offer comfort under uncomfortable conditions

Many nutritional adjustments, management procedures, and feed additives are used to reduce the negative impacts of heat stress. The use of phytogenic feed additives (PFA) is becoming increasingly popular as the modes of action of this technology are better understood.

Phytogenic ingredients such as assorted spices, flavonoids, and essential oils have been shown to produce positive effects in mediating the negative impacts of heat stress. A trial was conducted at University of Arkansas to assess the benefits for broiler production performance under heat stress conditions by inclusion of a specific phytogenic feed additive (Biostrong® Comfort, Delacon Biotechnik GmbH).

A total of 600, three-week-old male Cobb500 broilers were randomly assigned to environmentally controlled chambers in two environmental conditions of 12h/d cyclic heat stress (HS) (35°C) or thermoneutral (TN) (24°C) for three weeks. Relative humidity averaged approximately 27 percent in TN and 24 percent in HS chambers over the course of the experiment.

Three phase, corn/soy diets were fed consisting of a Control (CON): basal diet and Treatment (PFA): basal diet + PFA (400 g/T). Statistical significance was declared at P<0.05. The results of this study indicated an overall reduced feed intake (FI) under HS conditions, when compared to TN conditions, as was expected. However, FI under HS conditions was significantly improved in the PFA group over the CON group resulting in significantly improved bodyweight as shown in Figure 1.

Likewise, the PFA group had a four-point improvement in FCR under heat stress conditions. Overall mortality for the study was approximately 3.6 percent with no significant differences between treatments. The deleterious effects of heat stress on carcass quality and yield are well known in the industry. The results of this study documented this effect between the TN and HS conditions. However, under HS conditions, the PFA group showed numerically higher carcass weight and breast meat yield as compared to the CON group. These results are indicated in Figure 2.

Phytogenics can maintain intestinal integrity

The performance improvements documented in the PFA group under HS conditions result from the underlying benefits of phytogenic ingredients at the cellular level. These benefits include improvement in the antioxidative status of the bird, reduced inflammation, and improved gut integrity. One commonly recognised measure of gut integrity is Transepithelial Electrical Resistance (TER).

As indicated in Figure 3, the TER of the PFA group after heat stress was significantly improved. The results of this study agreed with previous studies and literature of the benefits of phytogenic feed additives in mitigating the negative impacts of heat stress on broiler production.


Modern broiler breeds have a continuously increasing growth rate and feed efficiency, which coincides with a reduced heat tolerance. Housing broilers at high ambient temperatures adversely affects performance, intestinal integrity, immune response, and meat quality. Feed additives that alleviate the negative impacts of heat stress, such as phytogenic feed additives, are a valuable tool for maintaining the performance and profitability of poultry production.

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