Also known as Monday Morning Sickness, azoturia, set fast, and exertional rhabdomyolysis, tying-up is a common name for muscle metabolism disorders in horses. The clinical signs include muscle stiffness, sweating, firm painful muscles, elevated respiratory rate, and reluctance to move. Severe episodes of tying-up can also result in reddish-brown urine due to the presence of myoglobin (a protein found in muscle tissue) which is known as myoglobinuria.
Types of tying-up
Scientific research over the past centuries has significantly improved our understanding of tying-up in horses. Initial studies were limited because researchers were trying to identify a singular cause of muscle pain and cramping, while tying-up is actually a complex, multifactorial issue.
Whether your horse suffers from mild or severe tying-up, it has a significant impact on their well-being and will limit their performance. The more you reduce the frequency and severity of the episodes, the better your horse’s performance and health will be. It’s good to understand the basics, such as the different types of tying-up.
Sporadic (Acute) tying-up
Usually, a horse is presumed to have sporadic tying-up the first time it has an episode. Some horses are healthy athletes and tie up sporadically due to exercising in excess of their training level, electrolyte depletion, or dietary imbalances. When a horse has a repeated bout after being rested and gradually returned to exercise, an investigation of an inherent form of tying-up will likely be indicated.
Chronic tying-up
Many horses with intrinsic muscle defects will have repeated episodes of tying-up with minimal exercise even when following dietary and training recommendations. There are two types of chronic tying-up: Polysaccharide Storage Myopathy (PSSM) and Recurrent Exertional Rhabdomyolysis (RER). This article will focus on the causes and management of RER in racing Thoroughbreds and Standardbreds.
Recurrent Exertional Rhabdomyolysis (RER)
Causes
RER was initially believed to be a result from lactic acidosis, but research has showed an inherited abnormality in the way muscle contraction is regulated in the horse. The disease may lie dormant unless specific factors trigger the calcium regulatory system to malfunction. These factors include stress, excitement, lameness, dietary starch, and exercise at submaximal speeds.
Temperament has a strong effect on the expression of RER in both Thoroughbreds and Standardbreds. Nervous horses have a higher chance of RER than calm horses. Young fillies are more likely to have a nervous temperament than mares or male horses, and therefore are most commonly affected. Diet also has an impact, with Thoroughbreds fed more than 2.5kg of grain per day being more likely to show signs of RER.
As previously mentioned, there is no basis for the association between RER and lactic acidosis. Thoroughbreds and Standardbreds rarely develop tying-up during maximal exercise when lactate levels are high. In susceptible Standardbreds, tying-up commonly begins after 15 to 30 minutes of jogging, although clinical signs may not be apparent until after exercise. In susceptible Thoroughbreds exercising on the treadmill, an episode most commonly develops with intervals of walk, trot, and canter, and is less common if horses are allowed to gallop. At the racetrack, tying-up commonly occurs when RER horses are held back to a paced gallop.
Not managing the cause of the tying-up episode might eventually be career ending as the horse will continually become stiff after exercise, not want to move, produce more sweat, and sometimes have an increased respiratory rate.
Many performance horses can still live up to their athletic potential if the condition is managed properly.
Management
Prevention of tying-up in horses susceptible to RER is complex and multiple factors must be changed to decrease episodes. These are some of the things you can do:
- Reduce excitement and nervousness: Many stressed RER-susceptible horses respond to a regular routine and housing in a calmer environment with fewer horses and compatible companions.
- Daily exercise: Exercise in the form of turnout, lungeing or riding is very beneficial for RER horses and may help to reduce anxiety.
- Training adjustments: Thoroughbreds may benefit from more fast work than slow work. Interval training and reduction of jog miles to no more than 15 minutes per session will benefit Standardbreds.
- Diet: A nutritionally-balanced diet with appropriate caloric intake and adequate vitamins and minerals is the core element of managing RER. The challenge with hard-working racehorses is supplying enough calories in a highly palatable form to meet their daily energy requirements. Research suggests that less than 20% of digestive energy (DE) be supplied by non-structural carbohydrates (NSC = starch and sugar, e.g. cereal grains) and at least 20 – 25% of DE be supplied by fat (e.g. vegetable oil or rice bran).
- Supplements: Ensure your horse is receiving adequate sodium and chloride (salt) on a daily basis, and supplement with an electrolyte replacer like Kelato’s KelatoLYTE. Antioxidants are also beneficial for hard-working racehorses. Kelato’s LoosenUP contains a blend of vitamin E, vitamin C, selenium, magnesium, and chromium to aid in reducing the risk of mild exercise-induced muscle damage, soreness, and stiffness.
To effectively manage muscle problems in horses, it is important to identify the specific cause of tying-up. If repeated episodes occur, it is best to consult with your veterinarian and arrange diagnostic testing. Implementing an appropriate feeding, exercise and management program is essential to reduce the reoccurrence and severity of future bouts of tying-up.
Want to find out more? Get in touch on 1800 KELATO or email technical@kelato.com.au.
