Technical advice: Managing broilers in the heat

A cold spring, then a sudden spike in temperatures in early June this year, highlighted the more unpredictable weather patterns we’re now seeing in the UK and across northwest Europe.

And these sudden rises in heat and humidity can extend throughout summer. “Don’t assume once we’re into the second half of summer and shorter days that heat stress conditions in poultry are over,” warns Cargill’s commercial poultry manager David McBride.

“Producers need to be prepared for the unexpected when it comes to dealing with these sudden shifts in heat and humidity during summer.”

A combination of temperature and relative humidity (RH) cause heat stress problems. The temperature humidity index (THI) is taken as an industry benchmark for accessing heat stress in livestock systems.

“And recognising the thresholds at which heat stress is triggered helps us to mitigate the effects,” he adds.

Higher temperatures during summer affect the bird’s nutrient balance and this can reduce production of eggs and their quality, as well as growth rates in broilers (see Table 1). “We should look to counter this and acclimatise birds to temperature fluctuations.”

Feeling the heat

Poultry have four ways of expelling excess heat, depending on conditions. “At temperatures below 25⁰C with normal humidity – between 45% and 65% – birds will rely on one, or a combination of three, mechanisms. 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.

“But if temperatures rise above 25^oC, which can happen in poultry sheds if outside temperatures rise, these three mechanisms are not enough and birds will start to pant and lose heat through evaporation.

“If temperatures exceed 30^oC, evaporation becomes their primary cooling strategy and they’ll need vast amounts of energy and water. If humidity increases the effects of heat stress are greater.”

Nutrient problems

Birds suffering from the effects of hot weather will have reduced feed intake, which is nature’s way of reducing heat production from the digestion and metabolism of protein. 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 in broilers, due to a lack of energy. Energy reserves are used, instead, to maintain a lower body temperature.

Panting also leaves birds dehydrated and increases carbon dioxide (CO₂) in their breath from blood. This increases blood pH and can lead to a condition known as respiratory alkalosis with a resulting loss in electrolyte.

Periods of higher temperatures will also affect supplies if vitamin C, which is an important antioxidant and helps protect cells from oxidative damage.

“Even under moderately increased temperatures, the oxidative damage on the intestinal cells can cause significant damage and have an economic impact,” adds McBride.

“And this negative effect on gut health can destroy cells, which further decreases the transfer of water and nutrients into the body.”

Water-balancer

A better understanding of the effects of higher temperatures and humidity have enabled Cargill to develop solutions to counter the effects of heat stress.

Trials have shown that cooling products, which include Betaine, can help counter any adverse effects on production.

Betaine is a natural product. It has osmoregulatory abilities to help to maintain the water content of tissues and 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. Cargill has used Betaine in its poultry cooling product AviCool; part of its SolviTec range.

“AviCool also includes salts to stimulate water intake, which helps to keep the bird hydrated, and vitamin C to meet the birds increased requirements, 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.

“Producers should be ‘at-the-ready’ and run a product like AviCool through the drinking water system for between three and five days when birds are being challenged by high temperatures and when dehydration is a risk; particularly in the later stages of the production cycle.”

Table 1: The effects of higher temperatures on poultry performance