Tying up, exertional rhabdomyolysis, or azoturia are terms used to describe muscle disorders in horses that result in massive contraction of the muscle groups along the rump and back of the horse. The condition is extremely painful and the horse may also sweat and have an elevated respiratory rate. Its onset is usually during or following exercise. In severe cases, the horse may pass a reddish brown urine caused by the presence of myoglobin, which is a muscle protein that leaks into the blood stream as muscles become damaged and is transported by the blood to the kidneys where it is excreted in the urine.
Tying up has been known to exist since the days when horses worked for a living. For instance, draft horses that worked all week and were rested on Sundays without having their grain ration cut back, developed signs of typing up on a Monday morning when returning back to work, hence the name “Monday Morning Disease”. Carlstrom, who studied the disease in 1932, concluded that draft horses given high amounts of non structural carbohydrates (NSC) such as molasses, were more likely to develop muscle damage with exercise, as were horses with a nervous disposition.
Horses prone to tying up can be sensitive to a number of different things, and what triggers an attack in one horse may not necessarily do the same in another and horses sometime tie up for what appears to be no reason at all.
Possible Causes of Tying Up Genetics and Type Certain blood lines are known to be more prone to tying up as are certain breeds and young thoroughbred fillies in hard training and racing for instance have a higher incidence of tying up.
Soluble carbohydrates (cereal grains) are normally digested in the horse’s small intestine by natural enzymes, and if not properly digested there, result in undigested starches flooding the hind gut or large intestine where they are not wanted. The microbes that are present in the hind gut then undergo a “population explosion” as they feed on these undigested starches, and one of the products they produce is lactic acid. This causes a drop in the pH level of the hind gut, creating an environment not suited to the microbes. As a result, these microbes begin to die and release andotoxins in the blood stream. These circulating andotoxins most probably contribute to tying up as well as being the most noted cause of laminitis.
These undesirable, undigested starches in the hind gut also cause fluctuations in the blood glucose levels and circulating hormone levels such as insulin, as well as increasing the heat of digestion.
Performance horses that are prone to tying up greatly benefit from having the level of starch in their diet reduced, or enhancing the digestibility of these starches by processing first (micronization for example) before feeding as energy sources.
As the horse has evolved, continuously feeding on high fibre food sources, tying up is also greatly reduced by introducing into the diet, highly digestible fibre sources such as sugar beet, soya hulls, or lucerne and adding oil or fat to the diet if higher energy feed sources or better conditioning is required.
Balanced vitamin and mineral levels, especially Vitamin E and Selenium
During exercise, free radicals (highly reactive forms of oxygen which destroys cells in the body) are produced by the body. In the process of breaking down (oxidizing), carbon containing compounds (carbohydrates, protein and fat which are fed as energy sources), oxygen is used and carbon dioxide and water are produced. When water is formed from oxygen, a free radical is produced, which if not destroyed, can damage living cells. Antioxidants are present within the body to destroy these free radicals before they damage the cell, and Vitamin E and Selenium are two very important antioxidants.
Performance horses require large amounts of energy to perform to their best. They therefore produce far more free radicals compared to horses doing light work, and therefore require a higher level of antioxidants in their diets, which is probably why horses who are prone to tying up seem to benefit from Vitamin E and Selenium supplementation.
Electrolytes are an essential part of all body functions and maintain a sensitive electrical balance across muscle cell membranes. When muscles contract during exercise, nerve impulses stimulate a change in the chemical gradient and these electrolytes move across the cell membranes. The five important electrolytes in a horse (sodium, chloride, potassium, magnesium and calcium) must be present in specific ratios. As performance horses can lose large amounts of these electrolytes in their sweat and because of the important role that these electrolytes play in maintaining muscle cell integrity, it is imperative that lost electrolytes are replaced in the correct balance to prevent an episode of tying up.
Blood Analysis as a Diagnosis of Tying Up
Diagnosis of tying up can be confirmed by elevated serum levels of creatine kinase (CK or CPK) and aspartate amino transferase (AST or SGOT) in the blood. CK and AST are muscle proteins that are released into the blood stream when muscle cells are damaged. CPK levels rise rapidly with muscle damage, whereas AST rises more slowly and takes longer to return to normal levels. Horses that tie up should not return to hard work until these enzyme levels are back to normal.
Hints on the Management of Tying Up
Horses prone to tying up should be fed diets that are low in soluble carbohydrates (starch), or if high energy feeds are necessary, the starch sources should be carefully selected.
For example, Cool Time, which is the Capstone feed of choice for such horses, contains a high level of micronized barley which is highly digestible in the small intestine (98%), as compared with feeding raw, crushed barley which has a poor digestibility (28%). The micronized maize contained in Cool Time is also well digested in the small intestine (over 90%), as compared to crushed or milled maize (under 50%).
Capstone Cool Time is the feed of choice for performance horses requiring high energy feeds that have a tendency to tie up. It contains micronized lupins and black sunflower seeds which are low starch, but high energy feed sources.
Increasing the level of fat in the diet is also very advantageous to horses prone to tying up, and the high level of Omega 3 rich oils in Cool Time is an added advantage. Should one require still higher energy levels, more oil (one to two cupfuls per day) can be added as well.
Horses that tie up are sometimes better off with an oat free diet. Cool Time does not contain any oats. Horses prone to tying up require a diet high in digestible fibre and feeds containing the so called super fibres (soya hull, beet pulp and lucerne) or good quality hays are recommended.
Horses prone to tying up should be fed a diet containing a good, broad spectrum vitamin, mineral and trace element supplementation such as the one found in Cool Time, and adding Capstone Excel Feed Supplement which contain high levels of antioxidants, can well be beneficial.
Capstone Electrolytes which have the same composition of as equine sweat are very effective to maintain electrolytes balance integrity within muscle cells and 30 – 60gms of Capstone Electrolytes added to your horses daily feed can be beneficial in preventing tying up.
The level of hard feeds on rest days must be reduced by half. Horses prone to tying up should be turned out daily and given light exercise on rest days wherever possible. Horses prone to tying up should have a period of slow warming up and cooling down respectively, prior to and after work.
An effort to reduce the daily stresses caused by the environment and stable management should be reduced wherever possible.