Dossier

Heat stress on farm

With increasing global temperatures, the risk of heat stress for farm animals is growing. As pigs are not able to sweat and in livestock houses they generally do not have the opportunity to wet themselves, an ambient temperature above the upper critical temperature leads to reduced welfare and performance. This upper critical temperature varies per pig category (including weight) and is considerably lower for lactating sows than for newborn piglets. At high humidity even lower temperatures can lead to heat stress.

Source photo: © WUR

This dossier aims to support welfare inspectors and other stakeholders in the field of climate control on pig farms, in particular at high temperatures. The dossier is updated periodically by the EURCAW-Pigs team. The text is not legally binding.

It is based on EURCAW-Pigs’ “Review on heat stress in pigs on farm”. Heat stress in all pig categories is described, with the focus on lactating sows and finishing pigs. Useful indicators for heat stress can be environment based or animal based. Room temperature, relative humidity, panting and pig fouling are recommended as the most useful and proven indicators for heat stress. Practical advices are given to prevent heat stress in pigs, beneficial for animal welfare, performance and working conditions.

Each EURCAW-Pigs dossier is divided in the following 5 items: 'Legislation', ‘Knowledge’, Tools for welfare inspection’ (Welfare indicators), 'Training courses' and 'Inspiring examples'.

There are hardly climatic legal requirements for pigs in the EU-regulations. However, on a national level rules can be stricter, but often formulated as “open norms”. Directive 98/58/EC states that the accommodation should “not be harmful” to the pigs, which can only be checked by animal based indicators. However, legal limits are not available in most countries, with difficult enforcement as a consequence.

Council Directive 2008/120/EC:

{Annex I, Chapter I, Article 3}: The accommodation for pigs must be constructed in such a way as to allow the animals to:

have access to a lying area physically and thermally comfortable as well as adequately drained and clean which allows all the animals to lie at the same time.

Council Directive 98/58/EC Annex: Buildings and accommodation

{Article 10}: Air circulation, dust levels, temperature, relative air humidity and gas concentrations must be kept within limits which are not harmful to the animals.

Measures to prevent heat stress can preferably be combined with the weather forecast to prevent heat accumulation in pig buildings. The main measure is to regularly check indoor temperature and relative humidity and to use a table on corresponding temperature-humidity-index values to assess the heat burden of animals and to start with countermeasures before the threshold is reached (see ‘Show more’).

Guidance

EURCAW-Pigs’ “Review on heat stress in pigs on farm” lists several measures to reduce heat stress in pigs:

Measures to reduce heat production

The feed ration can be lowered to prevent mortality and left overs in the trough.
To prevent arousal in the house, the feeding time could be postponed to cooler period, taking into account the legal requirements for feeding.
If possible, veterinary treatments should be postponed.

Measures to optimize climate management

Drinkers should be checked (flow rate, fresh, clean, cool) and ventilation rate maximized.
Incoming air can be cooled by water evaporation: water spraying (fog/mist) in the air inlet.
Air speed can be increased by inside circulation of air and at very high temperatures this could be combined by wetting the pigs.
Direct sunshine through the windows can be prevented by insulation or use of white chalk. Chalk or moisten the roof can also keep the roof somewhat cooler.
As pigs like to maximize heat loss by lying laterally without contact with penmates the caretaker shall try to maximize the space allocation per pig.

In the next section, welfare indicators are described, helping to detect (the risk for) heat stress in pigs on farm.

Source photo: ©Payola and Piriou, 2021

In the “Review on cooling technologies for pigs” technologies are described on cooling pigs kept on farms. This includes cooling of pigs, e.g. by sprinklers/showers, floor cooling, and fans for air circulation. Techniques also include those on cooling the environment, e.g. by heat exchangers, fog/mist, cooling pads, air conditioner, underground tubes, and underfloor air inlets. The knowledge in this review aims to support welfare inspectors in the field of climate control on pig farms, in particular at high temperatures.

Validity

Although temperature differences between countries during summer are large, the information and recommendations are valid for all European pig farms. There are not many legal requirements included in the respective EU Welfare Directives on indoor climate in pig houses, although some countries have more detailed rules. This implicates that inspectors need both animal based and environment based indicators to assess whether pigs experience heat stress and to enforce these open formulated legislative requirements by applying cooling technologies.

Upper critical temperature

Theoretically, heat stress starts when the ambient temperature exceeds the upper critical temperature of the thermoneutral zone. Above this temperature, pigs will actively increase heat loss to maintain their core body temperature. It should be noted that also between the upper limit of the comfort zone and upper critical temperature pigs already make adaptations to increase heat loss, but these changes do not affect heat production.

Active changes in pigs to increase heat loss are physiological, e.g., an increase in respiration rate. They may also include behavioural adaptations, e.g., lying on slatted floor instead of on an insulated solid floor. The upper critical temperature depends on age (body weight) and stage of production: when it is not exceeded it is both beneficial for animal welfare as for profitability.

Introphoto: (©WUR)

When visiting a pig facility it is necessary to have a toolbox of indicators to detect heat stress. There are many indicators available, both environmental (risk factors) and animal based, of which some show an acute, others a longer term effect (pen fouling) of heat stress. Individual indicators are not sufficient as a signal for heat stress, a combination of indicators is a better proof. The most useful and proven indicators are described in more detail in three indicator factsheets (see ‘Show more’).

Useful indicators for (the risk for) heat stress:

Panting and changes in respiratory rate: Changes in respiratory rate and panting are thermoregulatory behaviours which can indicate heat stress. Pigs have a very limited number of functional sweat glands. Therefore, the major way pigs thermoregulate is via behavioural adaptation, e.g. increase in respiratory rate.

Pig fouling: When pigs are dirty through manure/faeces on the body, this is due to inappropriate behaviour arising from unsuitable conditions on the farm, such as thermal stress, bad ventilation, overcrowding or pen and/or flooring design.

Ambient temperature and relative humidity: The upper limit of the thermoneutral zones of pigs is as low as 25°C in the end of the finishing period. For lactating sows the thermoneutral zone already ends at 21°C, heat stress starts beyond this temperature. High humidity will aggravate heat stress due to the reduced ability of the pigs to use evaporative cooling (e.g. by panting).

Source photo: ©WUR

In collaboration with national training bodies and national reference centers on animal welfare, EURCAW-Pigs develops training guides for the different welfare topics as standards for national training in EU Member States.

Learning goals

On the subject of heat stress of pigs on farm:

Updated knowledge about thermoregulation of pigs.
Knowledge about how the welfare of different production-categories of pigs is affected by heat stress on farm.
Knowledge about indicators for heat stress in finishers and lactating sows.
Tools for calibration and practical training in calibration – using the most validated indicators available.
Directions to prevent or reduce heat stress.
Knowledge about challenges in the communication with the farmers during inspection.

Inspection-driven welfare improvement

Additionally, EURCAW-Pigs provides examples of training plans and materials used in different Member States in English, to the extent possible, and training suggestions for improvement of communication skills and ways to support inspection-driven welfare improvement. This is presented on the training overview page.