Withers

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Wither redirects here. For the comic character, see Wither (comics).

For the family name, see Withers (surname).

Diagram showing the location of the withers.

The withers is the highest point on an animal's back, on the ridge between its shoulder blades. They are made up by the dorsal spinal processes of the first 5 to 9 thoracic vertebrae (every horse has 18 thoracic vertebrae), which are unusually long in this area and are less than 6" in height on the withers of the average horse. The height of the withers on a thoroughbred is 16 hands (5' 4").

[edit] Using the Withers for Measurement

The height of an animal is measured from the ground to the withers because this distance is fairly stable and predictable when the animal is standing still. Unlike humans, whose heads are in a fairly fixed position when standing upright and looking forward, many animals can move their heads easily into a wide range of positions when standing still, which makes the head a poor location for measuring the animal's height. The term is used primarily for four-legged domestic animals, such as dogs and horses. Horses are measured in a unit referred to as a "hand," which is equivalent to four inches.

To get an accurate measurement, the animal should be measured on flat, level ground and should be positioned so that it is standing squarely. In horses, raising of the head tends to lower the withers, and a lowering of the head raises the withers. Therefore, the animal should be measured with its head in a relaxed, "normal" position. Additionally, it is best if the feet are trimmed and shoeless when a horse is measured.

[edit] Conformational Issues

The withers of the horse are considered in evaluating conformation. Generally, withers of medium height are preferred, as high withers make it difficult to fit a saddle and are often associated with a narrow chest, and low withers do not provide a ridge to help keep the saddle in place and also decrease the area that muscles may attach to them.

More importantly, the dorsal spinal processes provide an attachment for the muscles that support the shoulder. Horses do not have a clavicle, so the shoulder can freely rotate backwards. If the vertebrae of the withers are long (front to back), the shoulder is more free to move backwards. This allows for an increase of stride length (and so it can increase the horse's speed). It is also important in jumping, as the shoulder must rotate back for the horse to make his forearm more parallel to the ground, which will then raise the animal's knees upward and get the lower legs out of the way. Therefore, the withers have a direct impact on one of the most important points of conformation: the shoulder.