Racing Greyhounds in Hot Weather
Heat related illnesses occur when the body’s cooling mechanisms are overwhelmed, causing the body temperature to reach a level that disturbs the normal cell function. This results in the release of chemical and toxins from cells, damaging organs (especially the brain, heart and kidneys), and can result in death.
The body’s cooling mechanisms can be challenged in two ways, exposure to a high environmental temperature (hot weather or hot car) or when the body accumulates heat due to strenuous exercise, known as exertional hyperthermia or exertional heat stroke [1].
In June 2020, a study into pet dogs admitted to veterinary practices in the UK for heat related illness, showed that greyhounds were the 5th most common breed admitted, four times more likely than most breeds[2]. This is because greyhounds, even though they have little fat and a thin coat, have high lean muscle mass – 60% of their bodyweight [3], and muscle produces heat when active (have you ever felt the warmth coming off greyhounds at rest?).
Greyhounds following even short periods of strenuous exercise, commonly exhibit significant symptoms of exertional hyperthermia, such as cramps and fatigue [4], as greyhounds expend almost as much energy in the first 7.5 s of a race as in the subsequent 22 s [5].
A high body temperature, either from exercise or the environment, and strenuous exercise alone all cause muscle fibres to break down (rhabdomyolysis) which causes the rapid release of chemical from the muscle cells as well as myoglobin, a protein that damages the kidney as it is cleared from the body, potentially resulting in acute kidney failure and death [6].
It could therefore be expected that greyhounds undertaking strenuous exercise in hot conditions would be at increased risk of developing rhabdomyolysis and myoglobinuria.
Unless myoglobin is measured in the urine, the kidney damage can go unnoticed, except in severe cases when the urine turns brown, and each exposure to myoglobin from racing or hot weather could damage the kidneys further.
The normal temperature of a greyhound is 37.5oC – 39.2 oC, the critical temperature for severe heat stroke when brain and organ damage occur is 41.5 oC.
An in-depth study into racing greyhounds in hot weather in South Australia, was published in 2016 – reference 7. It showed an average rise in greyhound rectal temperature of 2.1 oC after racing. If raced at temperatures above 31.2 oC the increase in body temperature was more than 2 oC and the study showed a significant increase in the number of greyhounds whose temperature equalled or passed the critical 41.5 oC. At 38 oC, 39% of greyhounds had temperatures above 41.5 oC.
Here is a telling quote from this Australian study:
“ …(there is) a common perception amongst trainers of greyhounds that, at ambient temperatures >30°C, the animals show signs of thermal stress such as panting, which concurs with evidence from experimental settings. However, as in South Australia there are more than 80 days in summer with maximum daily temperature >30°C (51), setting 31°C as a threshold for cancelling race meetings would represent major disruption to the industry.”
As the quote above and the graph of the temperature in Adelaide below show, greyhounds in South Australia are used to and acclimatised to running in temperatures of 30°C, yet they started to show signs of significant rises in body temperature at 31.2°C
The summer temperature in Great Britain is significantly lower than that of Australia, see chart below. Southend, Essex was taken as the reference point for Great Britain as it is close to several southern tracks which experience the higher temperatures in summer. The graph illustrates that the temperature in Southend is rarely above 25°C in the summer, implying this is the upper limit greyhounds in Great Britain are acclimatised to running in.
Every year most dog and animal welfare organisations warn against the potential danger of hot weather causing heat related illnesses (heat stroke/stress) in dogs, usually once temperatures reach 25oC, with extreme caution being advised at 28oC.
In 2018 the Society for Greyhound Veterinarians in Great Britain, released a statement:
“We would suggest that if the ambient temperature is in the region of 28oC-30oC serious consideration should be given to suspending racing and that racing should not take place in environmental temperatures in excess of 30oC.” [8]
Yet the Greyhound Board of Great Britain’s Hot Weather Policy advises that racing should be postponed at 33 oC [9] Note that the Hot Weather Policy is not part of the regulations, therefore there are no consequences from breaking it.
In most research, the thermalneutral zone/thermoregulation zone (the range of ambient temperature that energy usage is at a minimum and temperature regulation is achieved by non-evaporative processes[10]) is taken as 16-24 oC for greyhounds, at 25 oC greyhounds have to expend energy, pant, to cool down and maintain their normal temperature. The Greyhound Board of Great Britain use a thermal neutral zone range of 10 oC – 26 oC with no evidence or reference stated. The thermal neutral zone is more relevant to kennelling and travelling.
Factors that increase the risk of heat related illness: dehydration, high humidity, poor ventilation, stress of travelling, muzzling, antihistamines and anxiety[12]. All of which greyhounds can be exposed to before and after racing.
An important risk factor for heat related illness is the rapid change in ambient temperature – lack of acclimatization. Dogs begin acclimatization after around 4 days, but it may require up to 20 days to complete[12].
The table below listing the days when the temperature at Southend was above 28oC, (taken from information on Weather Spark) shows how little exposure and acclimatisation greyhounds in Great Britain get to temperatures above 28oC.
Without a study similar to that in Australia, it is not known at what temperature greyhounds in Great Britain start to increase their body temperature significantly to put them at risk of heat stroke.
| Temperature Range | Number of Days 2018 | Number of Days 2019 | Number of Days 2020 |
| 28o – 30oC | 14 | 3 | 9 |
| 30oC – 33oC | 3 | 5 | 1 |
| Above 33oC | 0 | 1 | 2 |
This table also shows how few races would have to be cancelled if the advice from the Society of Greyhound Veterinarians to postpone racing at 30oC was followed.
References
1. Medical progress – heat stroke. Bouchama, Knochel. N Engl J Med (2002)
2. Incidence and risk factors for heat-related illness (heatstroke) in UK dogs under primary veterinary care in 2016. Hall, Carter & O’Neill – Scientific Reports (June 2020)
https://www.nature.com/articles/s41598-020-66015-8
3. The proportions of muscle, bone and fat in two different types of dog. Gunn – Res Vet Sci (1978)
4. Metabolic Disorders of Racing Greyhounds. Blythe, Gannon, Craig – Care of the Racing Greyhound. Portland, Oregon, USA: American Greyhound Council (1994).
5. The Exercise Physiology of the Racing Greyhound. Thesis by Ross Staaden, Murdoch University (1984)
https://researchrepository.murdoch.edu.au/id/eprint/321/2/02Whole.pdf
6. Genitourinary Diseases in the Canine Athlete. Ferguson, Boemo – Canine Sports Medicine and Surgery. Philadelphia: Saunders (1998)
7. Influence of the Environment on Body Temperature of Racing Greyhounds. McNicholl, Howarth, Hazel – Front. Vet. Sci. (30 June 2016)
https://doi.org/10.3389/fvets.2016.00053
8. Greyhound Star — July 30, 2018
http://greyhoundstar.co.uk/greyhound-vets-definitive-hot-weather-advice/
9. Greyhound Board of Great Britain Hot Weather Policy 2020
10. . (Bligh 1973).
11. (Hales and Hutchins 1971)
12. Hyperthermia and Heatstroke in the Working Canine. Lori E. Gordon – Urban Search and Rescue Veterinary Group, Massachusetts