Understanding Equine Muscle Atrophy
Causes, treatment, and prevention of a common muscular problem in horses
Muscle is the tissue that turns a skeleton into a mobile body. Attached to bones via tendons, muscles contract and relax to maneuver that skeleton. Then there’s the smooth muscle that allows all sorts of functions that keep our horses alive and active, from digestion to tissue oxygenation. Muscular activity keeps legs moving, head turning, heart beating, and the lungs breathing. A common skeletal muscle issue is atrophy—the shrinkage or loss of muscle cells called myocytes. Stemming from a wide range of causes and linked to potentially serious diseases, muscle atrophy warrants a deeper look.
A Real Impact on Your Horse’s Health and Performance
With the crucial role musculature plays in every aspect of life, it’s easy to imagine the consequences of faulty, diseased muscles. “If muscle mass is insufficient, which can occur with muscle atrophy, a horse’s welfare can be significantly impaired,” says Alisa Herbst, PhD, postdoctoral associate at Rutgers, The State University of New Jersey, in New Brunswick, who recently developed and evaluated a muscle atrophy scoring system for horses. “For example, that horse might not be able to get up after lying down, or he might be unable to avoid an attacking horse,” she says. “Aside from compromised quality of life, horses with low muscle mass are limited in their ability to perform athletically. Lack of proper muscling increases the risk of injury, especially if high-intensity work or performance is requested.
“The full extent of the impairment on performance depends on the extent of strength lost from muscle loss compared to the amount of strength required for a given type and intensity of work or performance,” she adds.
We can divide the root causes of muscle atrophy into five main categories:
Sarcopenia is the Greek-originating scientific name for “age-related flesh loss.” It refers to a loss of muscle mass, quality, and strength, all of which are common in senior horses. In addition to giving geriatrics a sunken or skinny appearance, with the vertebrae and hip bones protruding, this generalized muscle loss can cause weakness. Some theories suggest sarcopenia is linked to inflamm-aging, a progressive bodywide inflammation affecting older horses and humans (Liang et al., 2022). In people it is also well-established that malnutrition correlates with sarcopenia (Ligthart et al., 2020).
Underuse of muscles leads to atrophy. Senior and retired horses are especially at risk of muscle atrophy because of naturally occurring sarcopenia, their tendency to develop pituitary pars intermedia dysfunction (more on that later), and the sedentary aspect of their lifestyle. Prolonged inactivity causes both atrophy and functional deconditioning of skeletal muscle, meaning muscle function is lost when unemployed. Muscle misuse can cause atrophy, as
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