Horse racing inherently poses significant risks to animal welfare. Racing horses in very hot weather places them at significant risk of dehydration and heat stress. However, there are no consistent rules that prohibit horse racing in Australia above a specific temperature.
Horses are particularly prone to heat stress due to their large body size, high proportion of active muscle and reliance upon evaporation to cool down through profuse sweating. These factors result in a rapid increase in core body temperature to critical levels during exercise and is further exacerbated during hot conditions . For Thoroughbred racehorses, the syndrome has been referred to as exertional heat illness (EHI) rather than heat exhaustion, with different factors involved therefore requiring different treatment methods, including sedation and anti-inflammatory drugs .
During a race, animals will exert considerable energy, thereby increasing their core body temperature due to the heat generated by working muscles with this eventually leading to fatigue. When the air temperature is high, the risk of heat stress is greatly increased. Prolonged and untreated heat stress can lead to dehydration, collapse and death. Horses can also suffer colic and kidney failure. Individual animals will respond to excess heat differently, but on very hot days most animals will be affected in some way. When horses overheat their bodies will attempt to reduce body temperature as quickly as possible by sweating.
Generally speaking, it is up to individual racing clubs to decide if races should be cancelled or rescheduled during very hot weather to minimise the risk of heat stress. Some state racing bodies have developed ‘heat’ policies which provide guidance on the factors that should be considered when deciding to cancel races or race meetings, but they do not prescribe a maximum temperature at which to cancel races.
It is noted that several racing clubs have cancelled or postponed races in recent years due to very high predicted temperatures. However, this action is not consistent across all clubs or states. RSPCA Australia supports the development of mandatory welfare standards for all racing codes which include provisions to cancel races in weather above a specific temperature. Addressing this issue requires urgent attention given climate change predictions that hot weather events will become more frequent in the future.
 Lindinger MI (1999) Exercise in the heat: thermoregulatory limitations to performance in humans and horses. Canadian Journal of Applied Physiology 24:135–146.
 Brownlow MA, Dart AJ and Jeffcott LB (2016) Exertional heat illness: a review of the syndrome affecting racing Thoroughbreds in hot and humid climates. Australian Veterinary Journal 94(7):240-247.