Feeding Horses that Tie-Up - Haylage can help
Tying up is a painful muscle condition that presents a major problem for working horses and affects a horses performance, health and wellbeing. There are several forms of tying up that a horse can be affected by, but the two most common are polysaccharide storage myopathy (PSSM) and recurrent exertional rhabdomyolysis (RER). PSSM most commonly affects quarter horses, draft horses, warmbloods and some arabians and their crosses while RER is most commonly seen in thoroughbreds as well as some standardbreds and arabians.
Because of the varying forms of tying up there was much confusion for years as to how it should be managed. Now with a better understanding of the varying underlying conditions we have a better understanding of how management can reduce the incidence and severity of the disease in affected horses. Providing a suitable diet for affected horses plays a pivotal role in their effective management. We will look at the best dietary strategies for the management of PSSM and RER but first let’s take a quick look at what causes these conditions.
Polysaccharide Storage Myoptahy (PSSM) – In normal skeletal muscle, glycogen (a polysaccharide or sugar made up of multiple glucose molecules), is stored for the muscles to use as a source of energy during exercise. In horses with PSSM the muscles store abnormally high amounts of glycogen PLUS they accumulate some ‘abnormal sugars’ (polysaccharides) in specific muscle fibres. PSSM horses appear to be particularly sensitive to insulin (the hormone that instructs muscles to take up glucose and store it as glycogen) which is thought to contribute to the higher than normal glycogen accumulation in their muscles. Interestingly PSSM horses are able to utilise glycogen in the same way unaffected horses use it during exercise so glycogen utilisation isn’t part of the problem.
Recurrent Exertional Rhabdomyolysis (RER) – Horses with RER have a defect in calcium regulation inside their muscle cells that results in excessive muscle contraction and muscle damage. Stress appears to increase the risk of an episode of tying up occurring with nervous fillies often reported as the horses most frequently affected.
Symptoms of tying up will vary depending on how severe the episode of tying up is. In mild cases, horses may simply seem lazy or tired. They may appear to have a lameness that is hard to pinpoint and may have some evidence of tense muscles. In more severe cases, a horses heart and respiratory rate may be elevated, they may sweat profusely and be reluctant or completely refuse to move, show signs of tremors around the flank, have tense or hard muscles especially over the hindquarter and display distressed behaviours including pawing the ground and rolling. If left undiagnosed long term, tying up can lead to muscle wastage, muscle weakness, back pain and gait abnormalities.
On blood testing, affected horses will have increased levels of the muscle enzymes creatine kinase (CK) and aspartate transaminase (AST). These enzymes are normally contained within the muscle cells, but when muscles cells are damaged during tying up these muscle enzymes are allowed to leak out into the bloodstream. Dr Stephanie Valberg (University of Minnesota) suggests that a serum CK concentration of 800 U/L or greater 4 hours after exercise indicates probable tying up.
Both forms of tying up respond well to dietary changes that reduce the intake of starch and sugars and increase the intake of digestible oils. While dietary changes for PSSM and RER horses are similar, the changes to diets for PSSM horses need to be a little more aggressive so we will look at them individually:
The key to managing horses with PSSM is to remove as much starch and sugar from the diet as possible to reduce the amount of glucose available to the muscles to accumulate glycogen. To do this, all cereal grain and cereal grain based feeds (so all feeds containing oats, corn, barley, wheat, rice, bran, pollard, mill run or any sort of cereal grain or cereal grain by-product) should be removed from the diet. Low sugar and starch (collectively known as non-structural carbohydrates or NSC) forages should also be selected and high NSC pasture, hay and chaff (including ryegrass, oaten and wheaten pasture, hay or chaff) should be avoided.
For horses in light work, low NSC forage, fed with an appropriate vitamin and mineral supplement may be all that is required. Horses in moderate to heavy work will however struggle to meet their daily energy requirements on a low NSC forage only diet. In this situation it is recommended that oil is used to meet up to 20% of the horse’s daily energy requirement (equivalent to approximately 3 cups of oil per day for a 500 kg horse in heavy work). Low NSC, high energy feed ingredients like sugarbeet pulp, soybean hulls, lupin hulls and copra meal can be also be used.
Horses with RER appear to still tolerate some degree of starch and sugar in their diet so the dietary restrictions aren’t as tight as they are for horses with PSSM. Current recommendations suggest that the amount of energy provided in the diet by high starch feeds (ie cereal grain and cereal grain based feeds) should be limited to 20% or less (approximately 2 to 2.5 kg/day for a 500 kg horse in heavy work) with the remainder of the diet being composed of forage and low NSC, high energy feedstuffs like sugarbeet pulp, soybean hulls, lupin hulls and copra meal.
Horses in light work that suffer from the RER form of tying up would again likely do best on a diet of low NSC forage with an appropriate vitamin and mineral supplement. Horses in moderate to heavy work can have oil (up to 20% of their daily energy requirement), grain based feeds and high energy, low NSC feedstuffs added to their diet as needed to meet requirements.
The diets for horses with both forms of tying up need to be carefully formulated to ensure the requirements for vitamins and minerals including antioxidants and electrolytes are met.
A note about oils – just adding oil to the diet of a horse that ties up won’t help reduce symptoms. Oils should ONLY be added to the diet of a horse with tying up where additional energy is needed in the diet. Only enough oil to meet energy requirements should be added. Adding oil just for the sake of adding oil or adding an amount of oil that exceeds digestible energy requirements will just lead to weight gain and obesity.
The amount of sugar and starch fed to horses that tie up, and particularly those with PSSM should be limited. Haylage® contains just 2.5% NSC on an as fed basis making it a perfect choice as a low NSC forage to use in the diet of horses prone to both the PSSM and RER forms of tying up.
Feeding low NSC forages like Haylage® reduces both the amount of glucose available for glycogen synthesis in the muscles and the post feeding insulin response (Borgia et al 2011) which should help to reduce glucose uptake by skeletal muscles. Both of the factors will help to control the formation of muscle glycogen in PSSM affected horses and therefore reduce the incidence and severity of tying up.
The low NSC forages that diets for horses that tie up should be based on are typically low in energy, which often makes it difficult to meet the daily energy needs for these horses.
University studies (Moore-Colyer and Longland 2000) show that the nutrients in haylage (like Haylage®) are more digestible than those in equivalent hay, making haylage higher in digestible energy. Using Haylage as part of the low NSC forage base of the diet allows you to meet digestible energy requirements in the overall diet more easily without having to rely so heavily on other feed ingredients that may be unpalatable or unsuitable.
It is important to keep all horses well hydrated but it may be of particular importance in horses that tie up. Dehydration has been implicated in endurance horses that have tied up and it is particularly important for a horse that has tied up to remain hydrated so it can clear the by-products of muscle damage through the kidneys without actually damaging the kidneys themselves.
Haylage® is a high moisture forage and may help to keep horses hydrated, particularly if they are away from home at competitions, in pain due to a recent bout of tying up or just not very good at drinking enough water to stay fully hydrated.
While modifying the diet plays a huge role in managing tying up, dietary changes need to be made in conjunction with changes in overall management. Dr Stephanie Valberg reports that if only diet is changed in horses with PSSM 50% will show signs of improvement. But if both diet and exercise/management are changed 90% will improve.
Horses with both forms of tying up need to be managed closely to reduce stress, increase turnout time, reduce or preferably eliminate periods of confinement without exercise and to provide exercise that allows them to steadily build and maintain fitness. Overexertion must be avoided at all costs.
With close attention to diet and overall management horses that are prone to tying up can lead normal lives and are able to perform at the highest level.
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