Heat stress in birds occurs due to body temperature elevation. This is usually due to changes in ambient temperature and humidity conditions. The birds experience heat stress when their bodies are struggling to maintain a balance between the body heat production and the heat loss (i.e. their body temperature is beyond the thermoneutral range). According to some reports, about half of all chickens raised in the world suffer in some way from the effects of heat stress during the summer season.
Heat stress causes changes in behavior and body function, which ultimately affects growth and weight gain. For the poultry farming enterprises, this translates into a decrease in performance and therefore lower profitability.
Modern broiler and laying hen chicken cross breeds are particularly vulnerable to overheating. There are several factors that increase the risk of heat stress in birds:
- Heat insulating feather and down layer.
- No sweat gland on the skin.
- High body weight to body surface area ratio.
- Increased metabolic activity due to genetic selection.
All these factors negatively affect the thermoregulation and contributes to the body overheating. Possible flock overheating indicators are changes in feed and water consumption. When the body temperature is beyond the thermoneutral zone, there birds exhibit an increase in water consumption and a decrease in feed consumption.
Poultry Response to Heat Stress
The body overheating triggers a series of physiological and behavioral reactions intended to cool the body and restore the body temperature within the thermoneutral zone. Breathing becomes more rapid, blood drains from the gastrointestinal tract and rushes to the skin, head and scalp. The body seeks to reduce heat production and increase heat output. Feed intake decreases by up to 20%, the birds stop gaining weight and may even lose it later, egg production also drops. Quality of chicken meat and eggs deteriorates, immunity system performance also decreases and the risk of infection with various pathogenic agents increases.
Another manifestation of heat stress disruption of intestinal integrity, the so-called phenomenon of “leaky gut”. Reduced blood supply to internal organs gradually leads to depletion of the intestinal mucosa, the permeability of the membrane deteriorates, resulting in the body not being able to secrete important digestive enzymes. At the same time, the concentration of cortisol and pro-inflammatory cytokines in the blood changes. All this leads to impaired nutrient absorption and an increased risk of inflammatory reactions, as well as the penetration of bacteria from the intestinal tract into the bloodstream. Consequently, the likelihood of illness in an individual chicken increases and, in particularly severe cases, can even lead to the spread of the disease and the beginning of an enzootic or epizootic outbreak at the poultry facility.
Obviously, this can have disastrous consequences for the profitability of the business as a whole, so the management of this problem is crucial, especially during the summer season in countries with hot climates.
Combating Poultry Heat Stress
There are several options to combat the poultry heat stress, which can be classified into several types:
- Microclimate control;
- Dietary modifications;
- Treatment with special drugs.
The best results are achieved with the complex scope of measures, but depending on the situation, sometimes it is sufficient to use only certain individual methods.
Microclimate Control
This is the most obvious and easiest option. In most cases, it is sufficient to increase the heat exchange intensity inside the poultry plant. Improved ventilation, cooling of inflow air, air humidification, redistribution of air flows in the building, better insulation heat of the building, etc are all efficient measures. Usually heat is removed by ensuring removal of the waste heated air and inflow of cooler atmospheric air. Nevertheless, this method is effective only when the air outside of the facility is colder than indoors. If the ambient air temperature is high, the farms can use evaporation equipment or opt for installation of additional cooling machinery.
Installation of a complete set of climate control equipment may require a major retrofitting of the facility and may require high costs and be disproportionately expensive. It is preferable to build a facility with the consideration of local climatic conditions and featuring a well-developed integrated climate control system from the beginning. For example, EGGoist and MaxGrow poultry plants are built from insulated panels and incorporate integrated ventilation systems and air cooling and humidification systems. The building design take into account climate requirements for local conditions, including critical situations with unforeseen peak loads.
Dietary Modifications
The effects of heat stress in poultry can be mitigated by modification of feeding and drinking patterns. In addition to improving the microclimate, chilled water can be introduced into the drinking system. It is important to keep a temperature balance and to consider drinking systems and water consumption. It is not recommended to give too cold water, since it is considered bad for the health of birds. It is also important to consider the length of the drinking line and take into account the fact the water will gradually warm up and may not be cool enough at the end of the line.
There are also special feed grades with easily digestible proteins that reduce heat production during digestion, compared to regular feed. Choosing the right anticoccidial program is important; some anticoccidials reduce the poultry ability to cope with overheating, so the right nutrients should be selected to mitigate the negative effect. Feed supplements containing electrolytes, antioxidants and micronutrients can be used to boost the poultry ability to cope with overheating. Although, the effectiveness of such methods is extremely low, and they are not powered enough to eliminate all the effects of overheating.
Use of Special Supplements
The use of feed supplements has little to no effect on heat stress levels, but can reduce its effects and eliminate the resulting health damage. Special feed supplements with anti-inflammatory effects have been developed that reduce gut inflammation during heat stress. For example, isoquinoline (IQ) alkaloids can accelerate broiler growth due to their anti-inflammatory properties. Tohoku University in Japan recently conducted a study to investigate the effectiveness of feed supplemented containing IQ. 360 broiler chickens were divided into 2 groups, with the control group receiving the standard unchanged diet and the second group receiving IQ supplements with feed. Both groups were kept in the same climatic conditions within the a thermoneutral zone until day 14, after which they were artificially exposed to the heat stress. To evaluate the effect of heat stress, the poultry blood samples were tested for plasma fluorescein isothiocyanate (FITC)-dextran on day 42. This test enables assessment of the impaired gut barrier function and comparison between the groups.
The study results showed that the group that received IQ feed supplements had a lower level of FITC-dextran than the control group. This unequivocally indicates that IQ-containing feed supplements have a positive effect on the poultry health under the heat stress conditions. In addition, the birds in the IQ group consumed more feed than those in the control group; accordingly, they showed better weight gain rates.
Conclusions
The heat stress is a serious concern for many poultry businesses. In view of the fact the that peak temperatures in different countries are increasing every year, it is reasonable to expect that this problem will not go away with time. This means that the industry needs to master both existing and new ways to combat the poultry overheating issue. The most affordable and effective way is implementation of a proper microclimate and climate control system. Various supplements and feed grades are also effective to help birds cope with the effects of heat stress.
Installation of climatic equipment at the existing running plant can be overly expensive, so it is much more advantageous to construct a new plant with consideration of all contributing factors. A well-developed feeding and drinking systems also offer other additional methods to combat overheating and the effects of heat stress. Such solutions are implemented by TEXHA as part of its Multifloor integrated poultry plants. This is currently a new and proprietary technology already used in China and the United States.
Source: Poultry World