TELLTALE EVIDENCE:
White hairs over the wither area indicate previous damage.
The horse's withers are a vulnerable area for development of pressure
sores. The presence of white hairs, as shown in the photo above, is
evidence of previous damage to the hair follicles in the deeper layers
of the skin. Readers are, I'm sure, well aware of the importance of
saddle fit over the withers and the need to ensure that neither the
saddle nor the saddle pad puts pressure on this area. But did you know
that blankets can also put pressure on the withers? Especially
considering that horses may wear blankets for many hours at a time,
blanket fit can have a decided effect on a horse's comfort and welfare.
This article describes a study of how the style of a blanket affects the
way it fits and the pressure it exerts on the withers. |
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Pressure Sores
Pressure sores develop when sufficient pressure is applied to the skin to
impede blood flow in the small capillaries. The tissues supplied by the
occluded capillaries are deprived of oxygen, and nutrients and waste
products accumulate. Over time, the affected tissues deteriorate and die,
and a sore develops. The risk of developing a pressure sore depends on both
the amount of pressure and the length of time for which it is present. Even
a small amount of pressure, if applied for long enough, may incite an injury
of equal severity to that produced by high pressure, albeit in a shorter
time. Modern horse-blanket materials and their insulation are light in
weight, thereby producing a relatively small amount of pressure on the
horse's back; but even a lightweight blanket can cause a pressure sore if it
is worn for long enough. In colder parts of the country, it is not unusual
for horses to wear two or even three layers of blankets. With a total weight
of 20 kilograms (44 pounds) or even more, multiple blankets greatly increase
the risk of a horse's developing pressure sores.
The Delicate Withers
The withers are formed by the dorsal spinous processes of the first few
thoracic vertebrae. If you run your hand over the top of your horse's
withers, you can feel the prominences of the individual thoracic spines
beneath his skin. With no muscle or fat to cushion the bone, the withers are
particularly vulnerable to the development of pressure sores. This is why
horsemen must be vigilant in ensuring that tack and equipment do not put
direct pressure on the withers.
Blanket Styles and Wither Pressure
Horse-blanket manufacturers offer a range of styles, some of which include
modifications intended to relieve pressure on the withers. The goal of our
research study was to measure and compare pressure on the withers produced
by three styles of waterproof turnout blankets: V-free insert, cutback
withers, and straight-cut. The V-free insert style has a seam along the
center of the back and darts over the haunches so it fits the shape of the
horse's topline. A V-shaped insert on each side of the withers raises the
front of the blanket to accommodate the prominence of the withers.
The blanket with cutback withers is fitted to the shape of the horse's back
and croup. A U-shaped cut-out removes pressure from the most prominent part
of the withers, and the blanket used in this study also had sheepskin edging
to provide cushioning around the cut-out. This design completely alleviates
pressure on top of the withers but may result in a focal concentration of
pressure on the back part of the withers. The straight-cut blanket has no
seams over the horse's back, meaning that it is not fitted to the horse's
contours. The advantage to the straight-cut design is that, because there
are no seams, it offers maximal protection against moisture penetration.
For our study, we used an electronic pressure mat to measure the pressure on
the dorsal spinous processes of the withers in a group of twelve horses.
Each horse wore three blankets: a straight-cut blanket weighing 3.7 kg (8.2
lb), a blanket with cutback withers weighing 3.9 kg (8.6 lb), and a blanket
with a V-free insert at the withers weighing 4.5 kg (10 lb). We measured the
pressure from the base of the neck, just in front of the withers; to the
lowest part of the back, just behind the withers. The pressure mat has a
series of sensors, each represented by a rectangle. We inserted the mat
between the withers and the blanket, then walked the horse for five minutes
before taking measurements of blanket pressure on the withers with the horse
standing and walking.
Our Findings
In analyzing the data, we calculated the total force applied over the
withers, the maximal force applied to one sensor,and the area that was under
sufficient pressure to result in a pressure sore over time. The pressure
maps are typical of the patterns seen with the three blanket styles that we
tested.
The straight-cut blanket produced the highest total force summed over all
the sensors and the largest area of high pressure. With the straight-cut
style, the greatest pressure was located over the highest part of the
withers. The blanket with the V-free insert had the lowest total force and
the smallest area of high pressure while both standing and walking, despite
the fact that it was the heaviest blanket tested. Maximal pressure was
recorded at the back of the withers, around the area where the V-free insert
was attached.
The blanket with cutback withers produced force and pressure readings midway
between those of the other two styles, but the pressure was concentrated at
the back of the withers, as indicated by the arrow in. All three blankets
exerted higher pressures during walking than when the horses were standing
still. This effect was especially marked for the straight-cut blanket.
The Role of Conformation
We wondered whether conformation might have an effect on the pressure
patterns and best choice of blanket, so we measured the slope of each
horse's scapula as a simple indicator of shoulder conformation. Horses with
a more upright shoulder experienced higher forces on their withers,
especially with the straight-cut blanket.
Avoiding Pressure Sores
This research has confirmed that even lightweight blankets that are the
correct size for the horse can exert sufficient pressure on the withers to
induce the formation of pressure sores, especially if the blanket is left on
for long periods of time or if the horse has an upright shoulder
conformation. The style of blanket affects the amount and distribution of
pressure.
It is sometimes suggested that blankets be removed or reset frequently to
prevent pressure sores from forming. However, this practice carries a risk
of reperfusion injury when blood flow is restored in capillaries that have
been occluded by pressure. In some cases, the return of blood flow is
associated with inflammation and oxidative damage rather than restoration of
normal function. Therefore, prevention is the best option: Select a blanket
that provides relief of pressure over the withers. In the blankets we
tested, the presence of a V-free insert at the withers appeared beneficial
in reducing wither pressure.
In your own horse, you can assess wither pressure both visually and
manually. It is best to perform a manual evaluation when the blanket has
been on the horse for some time and therefore has settled into place.
Without disturbing the blanket's position, slide your hand underneath it on
one side of the withers; then move your fingers up and over the spinous
processes. Ideally, there should be space for your fingers to fit
comfortably over the entire length of the withers. If the blanket squeezes
your fingers, it is probably putting too much pressure on the withers. Next,
remove the blanket and look at the hair and skin over the withers. If the
hair pattern is disturbed and the hairs are damaged or broken, or if the
skin is thickened and crusty, these may be signs of uncomfortable pressure
from the blanket.
Meet the Expert
Hilary Clayton, BVMS, PhD, MRCVS, is a
world-renowned expert on equine biomechanics and conditioning. Since 1997,
she has held the Mary Anne McPhail Dressage Chair in Equine Sports Medicine
at Michigan State University's College of Veterinary Medicine, East Lansing.
The position focuses on dressage- and sport-horse-focused research. |
