Heat stress occurs when the body of an animal or a human generates more heat or is exposed to more heat than it can release. Outside the so-called thermoneutral zone, i.e., the range in which the normal body temperature can be kept constant without energy input, an active warm-up or cool-down is necessary. In humans and animals, warming up or cooling down is inevitably accompanied by restrictions in other body functions, such as a weakening of the immune system, reduced growth, decreased fertility, lower milk production, higher heart rate, reduced kidney function and urine output, lack of concentration, restricted respiratory function, and possibly psychological and emotional effects such as irritability. 

In other words, heat stress can impair an animal's health and always has a negative impact on its well-being. With many animals, the associated passivity is often misinterpreted, and heat stress is often only noticed when the corresponding signs are already quite prominent. 

The decisive factor is not just the temperature, but also the humidity. The point at which heat stress sets in is species-specific and – as in humans –varies from individual to individual. Depending on how they are kept, animals in human care are often unable to find relief from hot temperatures as they cannot move to a cooler place when their physical adaptability reaches its limit. Animal keepers therefore have a great responsibility and are obliged to take suitable measures to prevent or reduce heat stress in their animals. Animals must be able to escape the heat and, if this is not possible, at least be able to cool down. 

Cows and calves have difficulty tolerating high temperatures. In lactating, i.e., milk-producing, cows, heat stress has been shown to set in as early as 22 degrees due to the associated increase in heat production, and it intensifies noticeably with every degree. High-yielding cows as well as cows that have just given birth or are about to give birth are particularly sensitive. According to current scientific knowledge, calves react with signs of heat stress from around 26 degrees in the shade. If they are kept in sunny "calf igloos" at such temperatures, this often leads to an overheating of the body, which can even lead to death. Growing calves – especially fast-growing high-yielding breeds – are even less able than adult animals to adapt to extreme weather conditions. In hot weather, calves start to sweat, accompanied by breathing with increased frequency. In igloo housing, it is not possible for them to find a suitably airy or shady place as the available space is very limited. Calf igloos heat up very fast at high temperatures; often to such an extent that the calves even prefer to stand in the direct sun outside than in the igloo because inside the heat accumulation is unbearable.

Chickens cannot regulate their body temperature by sweating. They cool down with the help of the air sacs and dissipate heat via the comb and wattles, among other body parts. Signs of stress in chickens include lifting or sticking out their wings, panting and throat fluttering. Particularly on farms with very large flocks of several thousand animals, the high animal density in the barn in combination with the construction of the barns, the animals die an agonizing death by suffocation within a short period of time if the essential ventilation system fails. This is why permanent monitoring is necessary and an emergency unit must be kept ready.  

Pigs are also unable to sweat, which makes it difficult for them to regulate their body temperature. Important indicators for assessing heat stress are respiratory rate, skin surface temperature and their position when they are lying down, which requires close observation. Pigs naturally cool down in wallows. The mud layer cools and protects their sensitive skin from sunlight. However, such wallows are denied to almost all pigs kept in Switzerland, which is why relief must be found elsewhere.  

Unlike chickens or pigs, sheep are often kept outdoors. They are considered robust, frugal and adaptable. In fact, their needs are often neglected. Whether outdoors or in the barn, hot temperatures can cause considerable suffering for sheep, whereby their sensitivity to heat can vary greatly. Breed, age and shearing condition are just as important as individual adaptability, which varies significantly according to scientific studies. Pregnant sheep and sheep with lambs as well as animals with health problems react more sensitively to extreme weather conditions.  

A particular danger in terms of life-threatening heat build-up is also presented in small animal stalls, cages, terrariums and aquariums of all kinds that are exposed to the sun or housed in poorly ventilated rooms with trapped heat. For animals kept in such enclosures, often rabbits, small rodents, birds and cold-blooded animals such as reptiles, these can become a cruel death trap if cooling and ventilation are not adequately provided. The same applies to outdoor enclosures that do not provide sufficient retreats in the cooling shade. The drinking and bathing water must be changed daily, and the corresponding vessels cleaned when changing.

Increasing periods of heat and drought cause not only air temperatures but also water temperatures in bodies of water to rise sharply at times. Fish suffer in particular as a result: Garden ponds that are too small, too shallow or exposed to the sun without protection, cause heat stress and promote diseases when temperatures are high. Both often lead to the death of the animals. Plants, shady areas, good aeration, and a secured oxygen supply are essential prerequisites to ensure the well-being of the aquatic inhabitants. Animal welfare legislation stipulates as an absolute minimum a shaded water surface of at least 10 percent of the pond or outdoor tank and, for the latter, a current appropriate to the fish species. Exceptions with regards to shading apply during the winter months and when keeping the animals in natural waters with planted banks or in ponds with a water depth of more than 2 metres (Art. 15 Wildlife Ordinance FSVO).  

Even dogs that are particularly close to humans often suffer from their keepers’ disregard of their needs: Although it should be common knowledge that the temperature in a car parked in the sun rises dramatically within a short period of time, dogs are frequently left in vehicles even during the hot season. Such situations are agonizing for the affected animals and can easily end fatally, even if fresh air is supposedly provided by leaving narrow window gaps open. People often fail to realize that the heat build-up in the car cannot be prevented by leaving small window gaps open as there is no air circulation. Even on cloudy but muggy days, the temperature inside a vehicle rises considerably, turning even shady parking spaces or parking garages into heat traps. The insufficient air supply prevents the animals from exchanging heat through panting and evaporation, which causes stress that can lead to heat-related death as a result of a circulatory collapse. Other dangers for dogs in summer are scorching hot asphalt pavement, which can lead to burns on their paws, as well as sunburn on areas of the body with little hair, such as their nose or ears.  

Warm weather and direct sunlight also cause dogs to overexert themselves more quickly as jogging companions or when they are taken out for a bike ride, depending of course on their body condition and coat texture. Brachycephalic (short-nosed) animals are particularly sensitive to summer temperatures - this type of breeding, which deeply affects the animal's anatomy, favours severe shortness of breath even with the slightest physical activity.

If extreme summer conditions persist, wild animals can also become distressed. There is no legal obligation to offer aid in emergency, as there is with relation to people in immediate life-threatening danger (article 128 SCC). However, insects, hedgehogs, birds, and other animals are happy to accept water offered in suitable containers. Exit aids can be used to prevent water bowls from becoming insect traps.  

Animals are individuals with different characters, personality traits and sensitivities. This fact must also be taken into account in the context of dealing with the animals.  

Particular attention on hot days must be paid to heat-sensitive, older or sick animals as they need adequate cooling and rest periods. In order to make hot days as comfortable as possible, animal keepers must take all necessary measures. To ensure a good fluid balance, the animal must always be provided with easily accessible, fresh and clean drinking water. Cool places under trees or on the cool ground are preferred by most animals as a place of retreat in the summer months. In general, the animal's accommodation must be designed in such a way that it is protected from strong sunlight. If the animal is weakened, lies flat on the ground, breathes conspicuously or pants heavily and has pale mucous membranes, these may be signs of heatstroke, which requires immediate medical attention.

Water is one of the key factors in relieving heat stress, and the water quality is also crucial. Furthermore, it should be noted that water should be offered in a species-specific form that allows the affected animals to drink as needed. For drinking troughs, for example, it is important to ensure a sufficient flow rate for water intake. Nipple drinkers, for example, are often unsuitable for this.  

Which measures are appropriate depends not only on the animal species and the individual animal, but also on the specific situation. It is not possible to pass a general judgment as to whether a fan or a misting system is sufficient. In some cases, well-intentioned measures can even have a counterproductive effect if used incorrectly, for example by unintentionally increasing the humidity. This makes it more difficult for the affected animals to find a physical compensation. It is therefore of the utmost importance that animal keepers deal with the issue thoroughly and take appropriate measures even before temperatures rise. Precautions should not only be taken when the animals are already suffering. Instead, appropriate management and, if necessary, technical aids should be used to ensure that animals are protected from heat stress.

Animal welfare legislation stipulates detailed requirements for animal keepers. However, it is not possible to cover all dangerous situations for animals with specific regulations. Instead, in many cases the general principles of animal welfare law alone must be relied upon, which means that animal keepers have a great responsibility – even if specific regulations are lacking. They have the duty to inform themselves in good time about dangers and risks for their animals and to take the necessary precautions to ensure the best possible protection. Any person who keeps or looks after animals must feed and care for them properly and provide them with the activities and freedom of movement needed for their well-being as well as shelter where necessary (article 6(1) AniWA). According to article 3(1) AniPo, animals must be kept in a manner that does not interfere with their bodily functions or their behaviour, nor overtax their capacity to adapt.

Housing systems and enclosures must be fitted – among others – with places to rest and withdraw under cover, opportunities to assume exploratory behaviour, grooming facilities, and different climatic zones. Whether or not the care is suitable, is assessed according to the experience and current knowledge concerning physiology, animal behaviour and hygiene in relation to the needs of the animals (article 3(2 and 3) AniPo). A special duty of protection for animal keepers applies in accordance with article 6 AniPo with regard to animals that cannot adapt to the weather conditions. This regulation does not only apply to particularly sensitive animal species. Rather, the individual and the specific situation must be assessed.

For example, protective measures must be taken for both sheep, which are generally regarded as robust and adaptable, and animal species that are known to be more sensitive to sunlight or heat. Domestic animals that are permanently kept outdoors are considered more resilient than animals that have become accustomed to stable conditions. However, the confusing wording in article 36(1) AniPo, according to which domestic animals “must not be exposed to extreme weather conditions over a prolonged period of time“, must follow a narrow interpretation according to case law. Protective measures are primarily intended to prevent imminent negative effects, which is why they must be taken before actual negative effects occur (ruling of the Administrative Court of Zurich of March 16, 2023, VB.2021.00839, E. 4.2.3).

To take no precautions is therefore only permissible in situations in which it is possible for each affected animal to adapt easily, for example by escaping the weather on its own or by cooling down. Only particularly spacious and well-structured enclosures generally allow this, which is why there is almost always a duty requiring action in anticipation of high temperatures. Suitable natural or artificial protection – for example a shelter – must allow all animals simultaneously enough space and shelter against rain, wind and intense sunshine, as well as a sufficiently dry lying area (article 36(2) AniPo), whereby the FSVO Ordinance on the Keeping of Livestock and Domestic Animals stipulates species-specific minimum area requirements. Suitable measures must also be taken in Alpine pasturing regions to ensure that the animals' rest and protection needs are met (article 36(2) AniPo).

Due to the principle of individual protection under animal welfare law, it must be ensured that each individual animal can adapt and not just the majority of the herd, flock or pack. A single animal that is overstrained in its ability to adapt and suffers or is harmed as a result of the animal keeper's failure to comply with their duty of care is sufficient to constitute mistreatment of animals under article 26(1)(a or b) AniWA from an objective point of view.

Since affected animals are usually not able to draw attention to their distress, not only animal keepers but all persons are called upon to be vigilant. In the event of a problematic or dangerous situation for the animals, the animal keeper must be contacted immediately to rectify the situation. If there are already signs that the animals affected are overstressed, the situation must also be reported immediately to the responsible cantonal veterinary service and the police. 

Animal keepers who fail to take the necessary measures in good time – such as providing adequate protection from the weather – are liable to prosecution. The offense of disregarding the regulations on animal housing in accordance with article 28(1)(a) AniWA can be considered – but only if no serious danger to the welfare of the animals has yet arisen. From the point at which the welfare of individual animals is seriously endangered because their adaptability is overstretched, this constitutes neglect in accordance with article 26(1)(a) AniWA. 

If pain, suffering, damage or fear actually occurs in an animal, the animal keeper’s behaviour must be qualified as mistreatment by omission – based on their duty of care according to article 6(1)(b) AniWA – within the meaning of article 26(1)(a) AniWA in conjunction with article 11(2)(a) SCC. If the heat stress even leads to the death of the animal, the animal keeper is liable to prosecution for killing the animal in a manner that causes suffering under article 26(1)(b) AniWA. 

Anyone who leaves their dog or another animal in a parked car at high temperatures is liable to prosecution for (possibly attempted) mistreatment or even killing in a manner that causes suffering under article 26(1 or 2) AniWA. 

Anyone who becomes aware of a dog in an overheated vehicle should first try to locate the dog's owner. If this is not possible within a reasonable period of time, the police or fire department should be alerted, so that they can free the animal with appropriate tools. If the dog's life is already in acute danger and it is no longer possible to wait for them to arrive, third parties are authorized to rescue the animal – even if this involves (necessary) damage to the car. In such a situation, the animal rescuer can claim to have acted in the presumed interests of the animal keeper – in legal terms, this is known as acting without due authority or under presumed consent. The animal keeper will therefore have to bear the financial loss caused by the damage himself, provided that proportionality is ensured.