HOW-TO SESSION: FEEDING FOR FITNESS MFM in Arabians


Arabian endurance horses diagnosed with MFM usually have a history of intermittent elevations in serum CK activity after endurance rides (10,000 U/L) or during exercise that follows a week or more of rest.5 Horses do not always show the same de- gree of pain, sweating, and reluctance to move, as is frequently seen in other forms of acute ER. Myo- globinuria can be observed in horses with only mild muscle stiffness. Between episodes, the heart rate, lactate, CK, and AST responses to exercise are nor- mal. The basis forMFMin Arabian horses appears to be related to a need for enhanced cysteine synthe- sis, decreased cysteine-based antioxidants, and oxi- dative stress.31


3. Management of Chronic Exertional Muscle Disorders


Altering diet and exercise regimes to compensate for underlying defects is often the best available strategy to assist horses with exertional myopa- thies. Identifying and eliminating any known factors that trigger ER are also important in pre- venting further episodes. Controlled treatment trials have been performed to validate management strategies for RER and PSSM1.26,32,33 Less evi- denced-based information is available with regard to management of PSSM2 and MFM, and recommenda- tions are based largely on retrospective studies or clinical impressions.17,34


4. Feeding Programs for Horses with Myopathies


A nutritionally balanced diet with appropriate ca- loric intake and adequate protein, vitamins, and minerals is a core element in treating all forms of exertional myopathies. As with all classes of horses, the development of a ration for these horses includes a series of steps.


1. Determine daily nutrient requirements. A horse’s nutrient requirements depend on age, breed, body size, growth rate, level of exercise, and other considerations. The Na- tional Research Council last published its rec- ommendations for horses in 2007.35 National Research Council requirements are often con- sidered minimums for many nutrients. Rec- ommendations that are more commonly used in practice are also available in commercially available softwarea,b.


2. Select type and intake of forage. Forage should be the foundation of every equine feed- ing program, so it is important to establish both the type and expected intake of forage before choosing concentrates or supplements.


3. Select energy sources in concentrate. One of the keys to managing exertional myop- athies is controlling the source of energy in a ration. Energy requirements in the US are expressed in terms of megacalories (Mcal) of


68 2020  Vol. 66  AAEP PROCEEDINGS


digestible energy (DE). DE can be supplied from nonstructural carbohydrates (NSCs), fat, structural carbohydrates (fiber), and pro- tein. NSC is the sum of water-soluble carbo- hydrates (WSCs) (sugars) and starch. Most concentrates fed to ER horses are low in NSC and high in fat. Unfortunately, determining the NSC content of commercial concentrates is not easy since these nutrients rarely appear as guarantees on feed tags or bags. Although the American Association of Feed Control Officials currently suggests that commercial feed products that bear labeling claims re- lated to carbohydrate content should include max sugar (ESC) and max starch in the guar- anteed analysis, there is not an agreed-upon method for measuring ESC and starch. There- fore, many state regulatory agencies do not al- low these nutrients to appear with other nutrient analyses such as protein, fat, or crude fiber. Feed manufacturers often sup- ply this information in supporting literature or on the internet, but these figures are not regulated by any governmental agency. Most feed manufacturers use Equi-Analytical in Ithaca, NYc to determine WSC and starch val- ues in feeds, and horse owners and veterinar- ians can also send feeds and forages to this lab for analysis.


4. Calculate intake of concentrate to meet energy requirement. The quantity of con- centrate required by a horse equals the DE requirement of the horse minus the DE supplied by forage. The DE requirement is dependent upon the activity level and the cur- rent energy status of the horse. DE require- ments will vary depending on whether the horse needs to lose, gain, or maintain its body weight.


5. Calculate intake of other nutrients (pro- tein, minerals, vitamins) provided from forage and concentrate. Most commercial concentrates are formulated to meet nearly all of the protein, mineral, and vitamin require- ments of the horse if fed at a typical level of intake as recommended on the feed bag. Of- ten, a horse will be fed below this expected range of intake and additional fortification will be required. This is particularly true when horses are fed high-quality forage or if they need to lose weight.


6. Supplement-required nutrients not pro- vided by forage and concentrate. Sup- plements are often necessary to provide nutrients not found in the forage and concen- trate, either because of low concentrate in- takes or to supply levels of nutrients that are greater than typically added to commercial feeds. Electrolytes, amino acids, vitamin E, and other antioxidants fall into this category for horses suffering from myopathies.


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