What climate change means for heat stress

Poultry industry must consider both short and long-term strategies to deal with coming changes.
Nathan Pelletier and Davoud Heidari
July 17, 2019
By Nathan Pelletier and Davoud Heidari
What climate change means for heat stress
Photo: Adobe Stock
In light of climate change, it’s increasingly important for the poultry industry to consider both short and long-term strategies to reduce and manage heat stress.

Heat stress arises when an animal is unable to dissipate sufficient heat to maintain normal body temperature – typically due to high ambient temperatures. It is one of the most common challenges producers encounter in flock management worldwide. Modern chickens are more susceptible to heat stress because they have been bred for production performance, which also means increased metabolic heat production.

As external temperatures increase, most chickens can regulate body temperature by reducing feed intake and diverting metabolic energy to thermoregulation activities, including wing spreading and panting. However, this has an immediate impact on feed use efficiency and egg production – with obvious economic repercussions for farmers.

Heat stress can also lead to reductions in egg weight, shell weight and shell thickness, in turn precipitating higher breakage rates. A variety of studies have further demonstrated the immune suppressing effects of heat stress, which can cause higher disease incidence and mortality. Heat stress, and a chicken’s efforts to thermo-regulate, intensify with temperature up to 40°C, above which risk of mortality from heat stroke becomes severe.

An early 2000s estimate of the cost of heat stress in the U.S. poultry sectors pegged annual economic losses at USD $128 to $165 million.

As the effects of climate change accelerate, record-breaking summer temperatures are becoming more common – both in Canada and elsewhere in the world. At the same time, recent climate change projection models point towards more rapid and larger temperature increases, and more frequent and prolonged extreme heat events than previously predicted. That said, they suggest the relative likelihood of such events will be quite regionally-specific.

This means that poultry flocks in some areas of Canada will be disproportionately vulnerable to heat stress risk looking forward compared to others. Understanding where and to what extent poultry will be most vulnerable, as well as identifying priority management and technology mitigation opportunities, is essential to helping the industry adapt to climate change.

A variety of options are available to mitigate or reduce the occurrence of heat stress in poultry. Some of these relate to dietary supplementation or manipulation. For example, researchers found a dietary supplement of 250 mg/kg of vitamin E before and after heat stress can partially reduce its effects.

Experts also found using the probiotic Bacillus licheniformis can lessen the impacts of heat stress on egg production, gut morphology and intestinal mucosal immunity. Some specialists also recommend timing feeding for early morning and afternoon during heat waves.  

Others have stressed the importance of leveraging the genetic basis of heat tolerance – in other words, selecting for breeds that can maintain high feed use efficiency while better tolerating high temperatures. Most work, however, has focused on direct technological strategies for reducing temperatures within poultry houses during extreme heat events, and cooling birds as poultry house temperatures rise.

Producers may use special equipment such as pad coolers, ventilators, foggers and roof sprinklers to cool poultry houses. Other strategies experts recommend include chilling drinking water, reducing flock densities and direct sprinkling of birds – although, with respect to the latter, negative interactions with ammonia levels and disease transmission are possible.

In light of the egg industry’s ongoing housing system transition, heat stress mitigation considerations should be integral to designing new houses. In particularly, builders and producers should pay attention to these facilities’ orientation, insulation and cooling infrastructure.

Producers will likely consider return on investment in selecting among options for heat stress management. Unfortunately, the relative efficacy of available technology and management strategies along with their costs is often unclear.

Stay tuned for future updates from the Food Systems PRISM Lab regarding: firstly, identification of high heat stress risk regions for poultry flocks in Canada; and, secondly, life cycle costing and sustainability assessment of alternative heat stress management and mitigation technology options.


Nathan Pelletier is Egg Farmers of Canada’s industrial research chair in sustainability, from the University of British Columbia – Okanagan. Davoud Heidari works with Pelletier at UBC’s Food Systems PRISM lab.

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