Muscle Myopathies : Mfm

Healthy muscles allow the horse to move and perform comfortably and efficiently, however there are a number of conditions which can cause dysfunction. The most familiar muscle myopathy is Polysaccharide Storage Myopathy (PSSM), where glycogen is stored abnormally in the muscle cells. A new development in the diagnosis of muscle issues is a condition now referred to as Myofibrillar Myopathy (MFM), which shares similar characteristics to PSSM, however the cause and management is novel.

In contrast to PSSM, MFM occurs when the alignment of myofibrils becomes disrupted. In normal muscle cells, a protein called desmin stabilises other proteins (actin and myosin), which are responsible for contraction, in order to create an orderly alignment within the muscle fibres. Muscle biopsies of horses with MFM found that the alignment of these contractual proteins is disrupted or broken, and desmin in turn then accumulates in these areas. Definitive diagnosis can therefore only be determined following muscle biopsy. MFM is found more typically in Arabian or Warmblood horses, first presenting between 6-8 years of age where CK or AST levels were normal following blood tests.

Signs and symptoms :

• Exercise intolerance or a general decline in performance
• Muscle soreness / stiffness
• Struggling to build or maintain topline
• Difficulty engaging and collecting
• Reluctance to move forward
• Dragging of the hind limbs
• Tying up (but rare)

Dietary Management

As with all muscle myopathies, diet and management plays a crucial role in maintaining the horses health and well being. As MFM is not a glycogen storage issue, the diet should not be focused on limiting muscle glycogen, and low starch, high fat diets are not required. Instead, supplying adequate levels of quality protein and increasing muscle protein turnover and strength is crucial.

Forage

As with any horse, horses with MFM should always receive a minimum of 1.5-2% of their body weight in forage on a dry matter basis per day. Having the forage analysed can be beneficial in determining the quantity of protein being supplied, however a forage with a high quantity of protein does not always mean that it has a high quality of protein.

Concentrates

The first priority when formulating a ration for a horse diagnosed with MFM should be that they are receiving a balanced ration which supplies all of the vitamins, minerals and quality protein that is not supplied by forage alone. It is important to ensure you are feeding the recommended intake of a fortified feed or nutritional supplement, and so the feed label should always be checked for recommended feeding guidelines.

Unlike horses with PSSM, horses with MFM tolerate moderate levels of non-structural carbohydrates (20-30%), with lower fat levels (4-8%) and higher crude protein levels (10-17%). As mentioned before, the quality of the protein is crucial, and ensuring that adequate amino acids are being provided, including essential amino acids such as lysine, methionine and threonine.

Supplementation

Nutritional supplementation is often key for horses diagnosed with a myopathy. All seem to benefit from antioxidant supplementation in the form of natural-source vitamin E and from omega-3 fatty acid supplementation in the form of a marine-derived oil. As performance horses sweat frequently, a research-proven electrolyte or salt should be offered daily.

Exercise

As well as nutritional management, exercise is of equal importance to managing a horse diagnosed with MFM. Surveys of owners with horses diagnosed with MFM suggest that horses with MFM benefit from days off of training to recover. The owners found that 3 days of exercise followed by 2 rest days (ideally with turnout) was the most successful training schedule. For some horses, exercising more than 3 days in a row meant an increase in stiffness in the following ride.

Warm-up routines were also investigated, and horses that were given 10-15 minutes on the lunge was found to be of great benefit. Working in a 'long and low frame' where the neck was released and the back was lifted was most beneficial, and engaging the hindquarters was not the intention. When under saddle, a similar long and low warm up before attempting any collected work, with rest periods to allow the horse to relax and stretch was also suggested. The duration of the ride was recommended to not exceed more than 45 minutes in more established horses.

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If you would like any further information, please feel free to contact our nutritional team on 01622 718487 or email info@saracenhorsefeeds.co.uk