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Snug, Warm and Hurting

An ill-fitting blanket can be as bad for your horse as an ill-fitting saddle,  By Hilary M. Clayton, BVMS, PhD, MRCVS

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.
Rub Marks

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.

Summary

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.

 

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