Effects Of Heat Stress In Poultry Birds

What is Heat Stress?

Heat stress in poultry is one of the most important environmental challenges adversely affecting poultry production worldwide (Kadim et al, 2008).

Exposure to extremes of heat affects poultry production on a worldwide basis and has a significant impact on well-being and production.

Heat stress in poultry occurs when the amount of heat produced by an animal surpasses the animal’s capacity to dissipate the heat to its surrounding environment.

This imbalance may be caused by variations in a combination of environmental factors (e.g. sunlight, thermal irradiation, air temperature, humidity, and movement) and characteristics of the animal (e.g. species, gender, and rate of metabolism)

The optimum temperature for performance is around 19 to 22ºC for laying hens and 18 to 22ºC for growing broilers.

When the thermorequirement of birds is not satisfied, heat stress in poultry may occur, depending on the strain, feathering, nutrition and production system.

Effects of Heat Stress In Poultry Birds

Heat stress generally affects the wellbeing and production indices of physiologically healthy birds.

Affected birds tend to limit feed intake and this has subsequent negative effects on growth and production performance.

Heat stress results in annual economic losses of $128 to $165 million in the poultry industry alone.

The total annual economic loss is $1.69 to $2.36 billion in the U.S. livestock industry (Lara and Rostagno, 2013).

High environmental temperature is deadly to poultry birds as it causes high rate of morbidity and mortality; thereby hazardous to human nutrition (Nienabar, 2007; Renaudeau et al., 2012).

A 10–20 times increase in the respiratory rate of birds causes increased CO2 loss through the lungs.

This loss results in an increase in the blood pH and ultimately disrupts the acid-base balance that deteriorate the health as well as performance of birds.

Heat stress can be chronic or acute. Sudden and short periods of extremely high ambient temperatures and humidity can result in acute heat stress.

An extended period of elevated ambient temperatures along with increased humidity results in chronic heat stress (Scanes, 2015).

Several scientific studies have reported that under thermal conditions, the feed conversion ratio (FCR) increases more in fast growing broilers than in slow growing layers influencing adversely the production cost.

Due to the fast metabolism of modern commercial poultry birds, more heat is produced and this makes the birds more sensitive to Heat Stress.

It is worthy of note that an elevated environmental temperature will affect the physiological, behavioural and immunological response of broilers and layers causing undesired consequences like electrolyte imbalance, endocrine disorders and immuno suppresion which will reduce profitability and other adverse consequences.

A proper understanding of the pathway and effects of heat stress in poultry is essential in order to craft various mitigation strategy to reduce consequential production loss as well as aiming at developing heat resistant poultry breeds for successful poultry production in hot regions of the world.

Effective Strategies For Preventing Heat Stress In Poultry

As profitable as commercial poultry production seem to be, challenges associated with heat stress can drastically reduce effective production indices of growing birds either broilers or layers.

Effective heat stress management require multifactorial strategies based on environmental modification, nutritional and gene selection strategies such as house design modification, genetics, thermoconditioning.

Poultry House Designs

Poultry houses should be designed to avoid the penetration of heat from the outside environment.

They should also be designed with maximum insulation to maintain their internal temperature (Scanes, 2015).

The direction of the poultry sheds should be from east to west in length and north to south in width in hot areas.

It is advisable to promote natural air flow from the north and south sides and to shield birds from maximum sunlight during the day; therefore the longitudinal direction of the shed should be from east to west.

Another factor that can avoid heat built-up is the condition of the roofing. Roofs should be clean, rust and dust free.

A shiny surface reflects solar radiation more than a dark or rusty roof.

The roof of the poultry shed should be steep and high.

Evaporative cooling systems can be used with cooling pads inside the shed, and sprinklers can be used in farms where environmental temperatures are high and humidity levels are low.

Use Of Exhaust Fan In Poultry Houses

Exhaust fans can also be used for the expulsion of hot air from the poultry house.

The distance between the sheds should be adjusted such that the flow of wind across the sheds is not interrupted and fresh air is available to the flocks (Simmons et al., 2003).

To achieve maximum air flow, the house should be open with internal re circulation fans (Donald and William, 2002) positioned in a tunnel ventilation arrangement (Lacy and Czarick, 1992)

Stocking Density

A high stocking density will result in ventilation failure.

The increased metabolic rate of birds during the summer increases heat production inside the poultry house, and the decreased loss of heat during hot and humid weather will increase the overall temperature of the poultry house.

The stocking densities should be adjusted according to temperature and humidity conditions in the respective area.

Intermittent Feeding Strategy

It has been noted that heat production increased with feeding level in poultry birds.

Several successful dietary modifications have been used to mitigate the harmful effects of increasing environmental temperature. Examples include Intermittent feeding programmes which could have possible applications in high-temperature regions where birds are minimally active during the dark hours consequently reducing the production of heat.

It is advisable that feeding should be conducted during the cool hours of the day, i.e., during the early hours in the morning and
during late hours in the evening (Farghly et al., 2018a), this strategy will reduce metabolic heat output as extra feed consumed during hot hours of the day will result in heat stroke and possibly mortality.

Early Feeding Restriction

Several studies have show that restricting access to feed at an early age is beneficial in preventing future response to heat stress in poultry birds.

Chicks subjected to up to 60 percent feed restriction at 4, 5 and 6th day of age have a lower susceptibility to heat stress when subjected to heat treatment at marketing age from 35 to 41 days of age.

The negative effects of the heat stress on the immune system of broiler chickens can also be alleviated by feed restriction early in life

Wet Feeding

Wet feeding has been found to be beneficial for heat stress in the rainy season in tropical environments.

Wet feeding improves feed consumption, which results in a better FCR in meat-type strains (Khoa, 2007; Afsharmanesh et al., 2010).

Lin et al. (2006) reported that wet feeding improves the performance in layer birds.

Moreover, wet feeding increases the passage rate of digesta through the gastrointestinal tract (Farghly et al., 2018b).

Water Management

Heat stress causes bird to consume less feed but their water intake increases astronomically. Hence it is important to ensure that cool water is made available during hot hours of the day as this will lower the body temperature of the birds.

The water:feed intake ratio at 15 °C is 1.82:1. However, when the temperature rises to 30–35 °C, the ratio increases to 4.9:1 (Holik, 2010). On average, for each 1 g of feed intake, birds consume 2–3 ml of drinking water during the winter and 4–5 mL during the summer. To keep the body temperature of birds stable, clean and cool water below 25 °C should be provided ad libitum and with ice added to the water.

Ensure that the water tank or reservoir is kept away from direct sunlight in a cool shady insulated area to prevent heating up the water flowing through the water system of the birds.

Drinkers should have sufficient water flow (> 70 ml/min/nipple), the water line should be checked by depressing each nipple tip against the saddle to ensure uninterrupted flow of water from the main line.

Litter Management

Extremely dry litter can further increase the house temperature during hot weather.

Dry litter can result in excessive heat and decreased humidity, and wet litter during the summer is indicative of increased humidity inside the poultry house

Make sure that the litter height is optimal and keep a thermohygrometer to measure the ambient temperature and relative humidity.

Dietary Supplementation With Vitamin, Minerals and Electrolytes

The decreased feed intake at high temperature also has repercussions on the intake of micronutrients such as Vitamin A, E, C, etc., which play important roles in the performance and immune function of poultry.

The supplementation of these nutrients might also be helpful for the maintenance of performance and immune function of heat stressed birds.

Vitamin supplementation of drinking water (Vitamin A, D, E and B complex) has been reported to be beneficial for the performance and immune function of heat-stressed broilers (Ferket and Qureshi, 1992).

Electrolyte therapy should be done to balance salts. Imbalances in acid-base balance occur in heat stressed birds.

Inclusion of various compounds in the diet or water is a common practice to alleviate the adverse effects of heat stress in poultry.

Genetic Selection Strategies

Selection of breed with intrinsic adaption to heat stress can be a major advantage in ensuring adaptation and tolerance to heat stress in poultry.

This could be of particular interest in ensuring that successive breeds are well adapted to extreme body heat condition and able to condition properly in regulating with the environmental body temperature.