How to combat heat stress in birds

Cargill Animal Nutrition’s UK poultry specialist David McBride advises producers to be prepared for increases in temperature and humidity.

Temperatures are rising and a heat wave is sweeping Britain, which means there’s additional pressure on poultry units. According to Cargill Animal Nutrition’s David McBride, even though the UK isn’t usually hit by such high temperatures, normal summer conditions call for extra care. “It’s not a problem confined to ‘hot’ countries – the combination of humidity and high temperatures can cause problems in in north west Europe too and we need to take measures to keep birds cool.  

“Higher temperatures during summer affect the bird’s nutrient balance with consequences on production, so we should look to counter this and acclimatise birds to temperature fluctuations during the summer months particularly.

“Sudden rises in environmental heat and humidity have been increasingly common in north west Europe. Even in May and June this year, we saw some erratic spells of hot weather. This challenges our day-to-day unit management,” he adds.

Temperature fluctuations are difficult to predict. “Just this April, temperatures fluctuated by 20⁰C within three days. This highlights why we have to be ready for the unexpected when it comes to dealing with these sudden shifts in heat and humidity during summer.”

How heat affects birds

The effects of elevated temperatures occur when the birds are unable to lower their own body temperature due to the failing of their natural thermoregulation systems. 

Poultry have four mechanisms of expelling excess heat. At temperatures below 25⁰C with normal humidity – between 45% and 65% relative humidity – then one of, or a combination of three, methods will generally suffice; they will radiate excess body heat through the air to other objects, convect heat into the surrounding air or conduct it through contact with cooler objects.

However, at temperatures above 25⁰C, the effects of conduction, convection and radiation are insufficient on their own, and the bird will also rely on the fourth mechanism of evaporation from the respiratory tract.

“Birds will pant to increase cooling,” says McBride. “And if temperatures exceed 30⁰C, evaporation is their primary heat loss strategy and the bird will require vast amounts of energy and water.”

If high temperatures coincide with high humidity, above RH 70%, then the effectiveness of cooling from this evaporation is significantly reduced, and the bird experiences greater heat stress.

If higher temperatures continue, birds will typically suffer from energy loss, dehydration and physiological stress.  Performance falls and mortality increases (Table 1).

Nutrient problems

Birds suffering from the effects of hot weather will have reduced feed intake and daily live weight gain is negatively affected. Broiler growth can appear to stall.

“Reduced intake is nature’s way of reducing heat production from the digestion and metabolism of protein,” says McBride. “The enzymes involved in breaking down food will become less efficient and nutrient uptake within the body decreases as the blood circulation to the digestive system is redirected to the skin to increase heat loss to the environment.

“We also see a decrease in lean tissue growth due to a lack of energy. Instead, energy reserves are used to maintain a lower body temperature.”

Prolonged panting causes digestive problems and leads to an imbalance of nutrients. This affects the bird’s health status and compromises bird welfare.

“Birds will become dehydrated due to water loss through evaporation. Their panting also increases the secretion of carbon dioxide (CO2) from blood in the breath as they exhale. This net loss of CO2 from the blood results in an increased pH and therefore higher alkalinity; a condition known as respiratory alkalosis.”

Electrolyte loss will follow, as the bird attempts to return the blood pH to normal and acidic H+ ions are re-absorbed into the blood in preference to potassium or sodium; the latter ions are then lost via the urine, which creates an ionic imbalance.

“Periods of higher temperatures will also affect supplies of vitamin C, which is required for the synthesis of the stress hormone corticosterone. So as the bird attempts to cope with these increased temperatures, it uses up supplies of vitamin C; a vitamin that is also an important antioxidant and helps protect cells from oxidative damage. If vitamin supplements are not provided the bird will quickly become comatose and die. “Even under moderately increased temperatures, the oxidative damage on the intestinal cells can cause significant damage and have an economic impact,” says McBride.

Lipid oxidation, caused by the increased stress on the cell membranes in the digestive tract, can also be a problem for birds in hotter weather and higher temperatures. This negative impact on gut health can destroy cells, which further decreases the transfer of water and nutrients into the body.

Betaine brings a solution

Trials have shown that cooling products that include Betaine can help to counter any adverse effects on production,” says McBride.

Betaine is a natural product. It is used in Cargill’s poultry cooling product Avicool; part of its SolviTec range. Betaine helps to maintain the water content of tissues. It is found in sugar beet molasses for example and it helps to control the balance of water inside the cells. Less water is therefore secreted and remains in the tissues, maintaining hydration and avoiding cell death.

A cooling product should also include a combination of salts to stimulate water intake, which helps to keep the bird hydrated, and vitamin C to meet the birds increased requirements in producing more stress hormone and, along with a naturally occurring antioxidant in the product, help to protect the cells from oxidation.

While building management will help to maintain optimum temperatures and humidity in poultry units, combatting the effects of hotter weather and the consequences of dehydration relies on maintaining the water content in tissues, maintaining the ionic balance and ensuring sufficient vitamin C is available.

“Liquid additives are available to help here,” says McBride. “Producers should be at-the-ready and run a product like AviCool through the drinking water system for three to five days when birds are being challenged by high temperatures and when dehydration is a risk; especially in the later stages of the production cycle. It’s a case of watching the weather forecasts and keeping ahead of the game, especially during the summer months.”

Table 1: The effects of higher temperatures on poultry performance