Although muscle cramping is a relatively common problem in racing greyhounds, the 
more severe form, described as Exertional Rhabdomyolysis (ER) is a rare, but potentially life threatening condition, commonly referred to a ‘muscle meltdown’.
The symptoms of rapid loss of weight, dehydration and wasting of backline and hindquarter muscles usually develop within 12-24 hours after a very stressful race, often under hot summer conditions.
Once you have seen a greyhound with the condition, you will not easily forget the extreme stress, pain and rapid deterioration that occurs, which if not promptly treated, can result in death within 48 hours.
Underlying Cause
Racing an unfit, dehydrated or overly stressed greyhound under hot conditions is often the major cause of the progressive cascade of weight loss and muscle wastage associated with ER.
Often the stressful over-exertion occurs when a lure chaser, or even a coursing greyhound, over-exerts when already dehydrated from hot conditions, travel or has an underlying electrolyte imbal-ance due to panting, barking or excitement prior to galloping.
One of the most common reasons leading to over-exertion, is the often extreme metabolic and physical stress imposed upona greyhound that misses being caught after a normal race and gallops another lap of the track under hot, humid conditions.
These conditions can also trigger a hyperthermia state with an acute, life-threatening elevation of body temperature above 41-42°C, with collapse and death within minutes to a few hours.
I will update you on this condition in the next article in the Star.
Typical Signs
Although the history of severe physical and metabolic stress gives an important clue to reason for the severe cramping, followed by weight loss and virtual muscle meltdown, the condition can have both a severe (hyperacute) and less severe form (acute).
The less severe form has symptoms that suggest a more acute form of cramping with stiffness when walking and a painful reaction when the backline and croup muscles are examined.
However, if this less obvious form is not recognised or dismissed as no more serious than a ‘bad cramping’ episode, if it is not managed promptly and expertly, the extreme stress can develop into a metabolic toxic reaction and the more serious or hyperacute form of ER.
In the initial reaction to the acute cramping of ER, the affected muscles swell rapidly due to the accumulation of high levels of lactic acid that is trapped in the cramped muscles.
The high level of lactic acid attracts water into the muscle tissue, causing them to ‘blow up’ with pain and inability to walk, as well as resulting in a relative dehydration in the blood and other body systems.
The problem is made more significant because of the bulk or volume of the muscle mass that is cramped and undergoing rapid internal structural breakdown due to the trapped lactic acid and low oxygen levels in the damaged muscle tissue.
The condition used to be referred to as hypoxic (low oxygen) rhabdomyolysis(HRM), but because it is associated with exercise and a severe metabolic cascade, the ER term is probably more appropriate.
The severe muscle meltdown or “lysis” and excruciating pain reduces the ability of the greyhound to walk, sit or lie down comfortably, with the initial muscle ‘blow-up’ virtually “dissolving” as the muscle tissue wastes away and the greyhound rapidly loses weight.
I have treated greyhounds that had lost up to 2-3kg within 24 hours after a hard race and have to be carried into the clinic because they are too weak and unable to support their own weight as the muscles are stripped away.
In the less severe form, greyhounds can walk, but dehydration and a high body temperature due to toxic shock can still result in toxic shock and muscle meltdown.
Dark Coloured Urine
One consistent sign is the passing of dark, port wine coloured urine within 2-3 hours after an ER episode, resulting from the leakage of myoglobin pigment from the large bulk of millions of muscle cells that are undergoing physical and metabolic breakdown as the muscles “melt down”.
The sheer volume of protein loss, enzyme escape into the blood and associated dehydration, if not recognised early and managed correctly, can lead to kidney failure within 48-72 hours after the initial severe cramping episode.
First Aid
First aid must be prompt and carefully carried out. The greyhound must be kept as quiet and as comfortable as possible.
If it is unable to sit up or walk, it should be allowed to lie down but turned over every 10 minutes to relieve the pressure and assist oxygenation of the underside muscles, to avoid even more rapid dissolution.
A small sling placed under the chest will help to take the weight off the limbs and pressure off the muscles.
If the greyhound has an elevated temperature, the muscles and body should be swabbed down with cold water to remove accumulated heat, but avoid excessive chilling.
The greyhound should be offered electrolyte boosted lukewarm water to drink, but in severe cases, most will refuse to drink because of metabolic stress, even when they are severely dehydrated with dry mouth membranes.
The first aid measures have only a supportive function to reduce stress and overheating prior to the greyhound being transported to a veterinary clinic.
Management
ER is a medical emergency! The animal should receive intravenous fluids under veterinary supervision to restore its blood volume and counteract the fluid loss and reduce the risk of kidney damage.
As less severe forms can develop into the hyperacute form with a risk of death, even mild cases should be put onto a drip and monitored over the following 24-36 hour period.
In fact, this supervision is similar to critical or intensive care given to sick or severely injured humans.
Injections of low doses of cortisone may be warranted in severe cases to prevent complete adrenal collapse which adds to the catastrophic nature of the severe form of ER.
A promptly treated greyhound will live to regain some of its muscle mass, but in my experience, it is best to retire the animal as its speed and form is often decreased.
Providing a well balanced diet, with adequate electrolytes and supplementation with a slow release potassium (600mg daily) tablet and Vitamin E (150iu daily) is a helpful aid to recovery and helps reduce the risk of a further episode, if a greyhound with the less severe form is deemed fit to return to racing.
Maintaining adequate fluid intake by soaking dry foods prior to feeding and ensuring a greyhound is fit and well hydrated prior to racing is an important safeguard against ER.
And, of course, being able to promptly catch a greyhound after a course or race, especially under hot conditions, is also an important measure to prevent ER in an otherwise fit and well prepared animal.
