Most farm animals will be transported at some point in their life. For example, animals may be transported to other farms, saleyards, feedlots, abattoirs or export ports. In Australia, the transport of pigs, poultry, cattle and sheep is quite common and, particularly for sheep and cattle, may involve journey times of up to 48 hours with no access to water or feed. Animals are usually transported in purpose-built trucks, which are open and exposed to the elements. Some rail transport of farm animals occurs but is less common. Transport is stressful for farm animals and, under Australian conditions, where maximum temperatures can easily exceed 40°C during summer, land transport particularly over long-distance journeys increases the risk of animal suffering [1, 2].
Farm animals’ ability to cope with extreme heat
An animal’s capacity to tolerate heat depends upon many factors, including breed, age, sex, size, metabolism, acclimatisation, and nutrition. Furthermore, different species have varying thermoneutral zones, i.e., the range of ambient temperatures in which the animal is able to regulate their body temperature without experiencing heat or cold stress.
Pigs have a thermoneutral zone between 16-25°C and poultry the range is 10°C-20°C. Both pigs and poultry are more susceptible to heat stress than sheep and cattle. Pigs are particularly susceptible because they do not sweat and have relatively small lungs, limiting their ability to cool down through panting. Growing pigs exposed to temperatures of 27°C may show signs of discomfort and distress and increased wallowing. If pigs are exposed to temperatures of 35°C for 24 hours or more, they are at risk of decreased intestinal function and may appear lethargic with muscle trembling .
The thermoneutral zone of dairy cattle is between 5C-20°C. For beef cattle, it varies between 15-25°C for British breeds (e.g. Hereford, Angus) and between 16-27°C for tropical breeds (e.g. Brahman). When temperatures exceed 35°C, cattle may start showing signs of heat stress such as excessive drooling and panting. Severe signs may include lack of coordination and trembling.
For sheep, the thermoneutral zone ranges between 21-31°C. However, the ability of sheep to cope with heat is also influenced by the length of their wool. Shorn sheep must be protected from direct sunlight to prevent sunburn which, when transporting sheep by truck, means that the frequency and length of stops should be kept to a minimum [2, 4].
How to reduce the risk of heat stress during transport
Heat stress is an important welfare concern and it is one of the main causes of mortality during the transport of farm animals [5, 6]. Two key factors – high air temperature and high humidity – increase the risk of heat stress because they reduce the effectiveness of body cooling mechanisms . On a transport vehicle, air temperature and humidity are mainly influenced by weather, stocking density (space allowance per animal) and ventilation. To reduce the risk of heat stress during transport, consideration must be given to:
- Transporting animals early in the morning, or during the coolest parts of the day and taking into account that, for most mammals, their body temperature is lowest in the early morning and highest in the afternoon .
- Reducing stocking density, i.e. providing more space per animal. Studies conducted in sheep  found that a reduced stocking density (0.26 m2/animal) maintains a lower Temperature Humidity Index (THI) in the truck compared to the standard space allowance (0.20 m2/animal). The THI is an important measure used to assess when conditions may cause heat stress for farm animals. For example, values of 80 THI or above indicate moderate to severe thermal stress . Thus, recording and monitoring THI before and during transport respectively is an important tool to help assess whether transporting, or continuing to transport, animals is advisable.
- Increased ventilation and provision of shelter. In Australia, most transport vehicles rely on natural ventilation. Thus, keeping vehicles moving and covering the front of the truck with a tarpaulin or similar are important mitigation strategies [2, 4]. In a study of sheep transport , it was observed that when sheep were transported under moderate ambient temperatures, a 3-hour stop caused severe thermal stress. If stops during the journey cannot be avoided, the duration of the stops should be minimal, and when stationary, vehicles should be positioned to maximise airflow .
- Cooling strategies. For example, to minimise the risk of heat stress in pigs, cooling strategies such as spraying pigs with water immediately after loading is recommended when temperatures exceed 27°C .
- Shortening the transport journey. Planning the journey efficiently and travelling along the most direct route to reach the destination as soon as possible will reduce journey time and the subsequent risk to animal welfare.
Should farm animals be transported during hot weather?
All participants in the transport supply chain, from farm to destination, must be aware of their responsibilities under the Australian Animal Welfare Standards and Guidelines – Land Transport of Livestock , which requires that reasonable steps are taken to minimise the impact of extreme weather on the welfare of animals during the journey and that animals are inspected regularly to ensure their ongoing welfare. Particular attention should be given to the above considerations and that animals have had access to cool, clean water prior to loading as well as immediately upon arriving at their destination.
Participants in the transport supply chain should be required to have standard operating procedures for transporting animals during hot weather and a plan for what is to be done during ‘extreme heat events’, including a decision whether to transport animals at all. Under Australian conditions, it is also relevant to develop clear and easy to follow strategies for exceptional transport during extreme heat, e.g. when needing to remove animals from bushfire threat, or paddocks where they have no protection from the sun. Coordination is required in the supply chain to ensure that the farmer, the transporter and the recipient all understand the risks and, their role and responsibility to help prevent animal suffering.
What is the RSPCA’s view?
Animals must not be transported in conditions that are detrimental to their welfare and place animals at risk of suffering. People responsible for the transport of animals have a duty of care to ensure that animals are not at risk of heat stress during land transport. Animals must be protected from adverse weather conditions during transportation and all journeys must be planned to avoid extreme weather conditions.
 Fisher et al (1999) The effects of long-haul transport on pregnant, non-lactating dairy cows. New Zealand Veterinary Journal 47(5):161–6.
 Fisher et al (2009) The influence of land transport on animal welfare in extensive farming systems. Journal of Veterinary Behavior 4:157–62.
 Fisher et at (2004) The effects of stationary periods and external temperature and humidity on thermal stress conditions within sheep transport vehicles. New Zealand Veterinary Journal 53(1):6–9.
 Caulfield et al (2014) Heat stress: A major contributor to poor animal welfare associated with long-haul live export voyages. Veterinary Journal (199) 223–8.
 Collins et al (2018) A systematic review of heat load in Australian livestock transported by sea. Animals 8, 164.
 Australian Veterinary Association Ltd (2018) A short review of space allocation on live export ships and body temperature regulation in sheep.
 Fisher et al (2002) The effects of stock crate design and stocking density on environmental conditions for lambs on road transport vehicles. New Zealand Veterinary Journal 50(4):148–53.
 Silanikove N (2002) Effects of heat stress on the welfare of extensively managed domestic ruminants. Livestock Production Science 67(1-2):1–18.