Stress and its Effecton Horses

Sources of Stress
The performance horse has many possible sources of physical and psychological stress to
contend with, including these:
• intense or prolonged exercise (whether in training or competition)
• adverse environmental conditions, particularly high heat and humidity, but also dust
and very cold or windy weather
• long-distance transport to and from shows (i.e. trips lasting longer than 6–8 hours)
• insufficient rest between athletic events or after long-distance transport
• lack of sleep at shows (e.g. late night events or activity in the boarding barn, stall too
small for the horse to lie down and rest comfortably)
• new experiences during training or competition
• confinement
• removal from familiar environment and social group
• changes in daily routine when traveling and at shows
• strange environment (e.g. boarding at shows)
• presence and activity of strange horses and people at shows
• increased stress levels in the handlers and rider
With repeated exposure, many horses become accustomed to most of these stressors, and
these activities or situations cease to be a significant source of stress. However, it takes
only one new or worrisome thing to stress a horse. And, as mentioned earlier, some
horses never quite adjust to all the extra stimulation associated with training, showing,

Effects on the horses health
The Stress Response
Regardless of the source of stress, the response by the horse’s (or the person’s) body is
the same. The stress response is a physiological, protective response to an event that
poses a threat (whether real or perceived) to the horse’s well-being. Physiologists
describe this response as readying the body for "fight or flight," although that phrase
implies a rather dramatic and immediate reaction to imminent danger. In less extreme
circumstances, the stress response is more subtle in its effects.
One of the key events in the stress response is the release of cortisol by the adrenal
glands. Cortisol is a hormone with wide-ranging effects on tissues throughout the body.
One effect, in particular, has important implications in athletic horses: cortisol decreases
the movement of glucose from the bloodstream into muscle cells (and several other types
of cells). This is meant to be a protective response, in that it conserves blood glucose for
essential functions, such as brain activity. However, in an exercising horse it decreases
the availability of this important energy source to the working muscles. As a result,
athletic performance is lower than expected for the stage of training.
Chronic cortisol release (i.e. chronic stress) also suppresses immune function, impairs
tissue healing, and causes a loss of muscle mass as amino acids from muscle proteins are
used to produce glucose. Thus, chronically stressed horses lose their “bloom” and
vitality; they look a little dull and they lack that spark which distinguishes winners from
the “also ran”s.
In addition, chronically stressed horses are more susceptible to infections. That includes
the contagious respiratory diseases (e.g. influenza, rhinopneumonitis [“rhino”], strangles)
as well as shipping fever (bacterial pleuropneumonia as a consequence of long-distance
transport). Recurrence of latent EPM (equine protozoal myeloencephalitis) or herpes
virus infection also is more likely when a horse is chronically stressed. Furthermore,
stressed horses are slower to recover from illness and from injuries (to which they, too,
are more susceptible).
One other common effect of chronic stress is gastric ulceration (stomach ulcers). Gastric
ulcer disease in horses is multifactorial. Stress (and the consequent cortisol release) is
only one of several factors involved; however, it’s a biggie. In survey studies of
performance horses, gastric ulcers were found on endoscopic examination of the stomach
in about 60% of show horses and over 80% of horses performing more intense athletic
activities.
It’s worth noting that in those studies only a small percentage of affected horses showed
obvious physical or behavioral signs of having gastric ulcers. What this indicates is that a
horse can be under sufficient stress to develop gastric ulcers without us being aware of it.
A study of cortisol levels in show jumpers illustrates this same point in a slightly
different way. In this study blood cortisol levels in three groups of show jumpers—
schooling level (least experienced), intermediate level, and open competition (most
experienced)—were compared, both at the home farm and at a show. As you might
expect, cortisol levels were higher in the schooling horses than in the more experienced
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horses, and they were higher at a show than at the home farm. But even in the seasoned
show jumpers, competition caused an increase in blood cortisol.