At the end of January, the first South African equine endurance congress was held. Attended by veterinarians and many others with a special interest in endurance riding, the congress was a great success, and the first of many to come.

The main speaker was the world-­renowned equine physiologist, Dr David Marlin. In one of his many interesting presentations, Dr Marlin addressed the topic of exertional rhabdomyolysis ("Monday Morning Disease").

Exertional rhabdomyolysis (ER) describes a syndrome in which muscle cells are severely damaged, resulting in the release of enzymes, and in severe cases myoglobin, into the circulation, and may occur in any type of horse after exercise. It may also occur following transport or general anaesthesia, particularly if this was for a prolonged period.

"ER is a common occurrence in ­endurance horses, and there are two main ­presentations," Marlin continued. "The first is the form of ER that occurs early on in a ride, often before the horse reaches the first vetgate. The second presentation is a form of ER occurring later in the ride, ­usually after half the distance in a 160 km ride."

The clinical signs vary, and can be as ­non-specific as an elevated heart rate to ­recumbency, although this is not common. ­Other signs include varying levels of pain, ­swollen muscles, being reluctant to move, have stiff gait, may walk but refuse to trot, be lame, exhibit a shortened stride, show ­reaction when muscles are palpated and signs of ­myoglobinuria (shown as red to brown coloured urine).

Treat them in time

Immediate treatment is essential, especially when myoglobinuria is present. Intravenous fluid administration at a rate of 15-23 litres/hour, at least until the horse passes urine, but preferably until the urine is clear, is essential. Painkillers should be used as required.

Extreme care must be exercised when using drugs such as Finadyne©, and these should not be used before the horse is rehydrated. With early and aggressive treatment the prognosis is generally good, once again depending on the severity of the attack.

The prognosis, as well as recovery from a bout of ER, will depend on the severity. In mild attacks the horse could be back in work after 1-2 weeks. Keep in mind that, although muscle tissue has a high capacity to regenerate and repair, this process may take several months in severe cases.

A number of contributing factors and/or causes of ER have been proposed, including electrolyte deficiency and/or imbalance, abnormalities in calcium metabolism, vitamin E and selenium deficiency, hypothyroidism, stress, over-exertion in animals not sufficiently fit for exercise, infection, heat exhaustion and genetic abnormalities such as polysaccharide storage myopathy.

Marlin added that, in his personal experience, horses that start rides with ­abnormal blood biochemistry, are at greater risk of developing severe early ­onset ER. There is also clear evidence that the ­elimination rate, especially as a result of metabolic conditions (of which ER forms part), increases with increasing environmental thermal stress (high temperature and humidity).

At the end of January, the first South African equine endurance congress was held. Attended by veterinarians and many others with a special interest in endurance riding, the congress was a great success, and the first of many to come.

The main speaker was the world-­renowned equine physiologist, Dr David Marlin. In one of his many interesting presentations, Dr Marlin addressed the topic of exertional rhabdomyolysis ("Monday Morning Disease").

Exertional rhabdomyolysis (ER) describes a syndrome in which muscle cells are severely damaged, resulting in the release of enzymes, and in severe cases myoglobin, into the circulation, and may occur in any type of horse after exercise. It may also occur following transport or general anaesthesia, particularly if this was for a prolonged period.

"ER is a common occurrence in ­endurance horses, and there are two main ­presentations," Marlin continued. "The first is the form of ER that occurs early on in a ride, often before the horse reaches the first vetgate. The second presentation is a form of ER occurring later in the ride, ­usually after half the distance in a 160 km ride."

The clinical signs vary, and can be as ­non-specific as an elevated heart rate to ­recumbency, although this is not common. ­Other signs include varying levels of pain, ­swollen muscles, being reluctant to move, have stiff gait, may walk but refuse to trot, be lame, exhibit a shortened stride, show ­reaction when muscles are palpated and signs of ­myoglobinuria (shown as red to brown coloured urine).

Managing recurrence

For horses with recurrent ER, changes in management are often successful. Regular daily exercise is essential (with no rest days). Changes in the diet, supplying a significant proportion of the energy requirement in the form of oil, with reduced grain intake. The electrolyte status also has to be investigated, and if at all possible, the electrolyte content of the feed should be analysed.

As excitement can play a role, it might be beneficial to use a low dose of acetylpromazine (ACP) 30-40 minutes before exercise, especially if the horse is to be exposed to something new or novel. Keep in mind that this cannot be used before a ride, as it is a prohibited substance. Other drugs are also available, but expensive if used in the long term.