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VETERINARY VIEWS
Topline muscles are strengthened when horses use their core abdominal muscles during exercise.
NEUROLOGICAL PROBLEMS
Muscles retain tone and symmetry through a series of neuromuscular responses as well
as muscle development related to activity, exercise, and conditioning. When one muscle group is visibly less developed than another, there could be an underlying pathologic problem such as occurs with invasion of the spinal cord by protozoan parasites, known
as equine protozoal myelitis, or EPM. These protozoa damage the central nervous system to varying degrees; sometimes all that is noticeable is atrophy of one or more muscles, whereas sometimes the horse develops an overt neurologic problem that would be dangerous to ride due to incoordination and instability. Muscle atrophy related to EPM can occur
in the haunches, along the topline, or in the shoulders. The horse may trot crooked or appear slightly unsteady and uncoordinated. In some cases, a horse with EPM may develop other deficits related to the cranial nerves
of the head, including blindness. EPM can
be diagnosed with a cerebral spinal fluid
tap, and medication is available to treat the condition. Some parts of the country have
a higher risk of contracting this disease, especially where opossums are prevalent; the protozoa are ingested by the horse when feed is contaminated with opossum feces.
Another neurologic deficit that causes an alteration in muscle tone and development is caused by mechanical injury to a nerve. In the
old days of draft use of horses, harness collars sometimes fit poorly, causing pinching of a major nerve in the shoulder. The result was sweeney, a neurologic condition that resulted in complete muscle atrophy of the shoulder muscles leading to a profound degree of muscle asymmetry. More commonly these days, a horse that suffers trauma to the shoulder area from a kick or blunt trauma may develop sweeney if there was associated nerve damage. The diagnosis of sweeney is based on a specific physical appearance of withered shoulder muscles, and also with EMG testing that measures the presence of electrical impulses in the muscles.
TOPLINE MUSCLING
When horses use their core abdominal muscles during exercise, they also strengthen the topline muscles. A horse that is allowed to move in a sprawled-out manner does little to build the abdominal and topline musculature and instead often appears rangy with weak muscling. The muscles beneath the neck become hypertrophied (overdeveloped) and the back weakens. This can lead to muscle pain
as well as affecting efficient locomotion and musculoskeletal comfort.
While exercise conditions muscle, it does not make muscle. Muscle synthesis and repair requires the essential amino acids as well as replacement of nutrients a horse uses while working. A well-balanced diet includes added
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SPEEDHORSE
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When harness collars were used and if they fit
poorly, they could cause pinching of a major nerve in the shoulder that led to sweeney, a neurologic condition resulting in complete muscle atrophy of the shoulder muscles. More common today, trauma with nerve damage can cause sweeney.