In the PAX program, the neck is rated in its length and orientation. If the length is very easy to measure objectively, it is not quite the same for orientation.
The good observation of the natural head position is when the horse is at a standstill, balanced and awakening, and that it is subject to no external stimulus (tissue, whip or bit of plastic at the end of the whip...).
The straight line joining the base of the 7th cervical vertebra at the base of the atlas forms with the horizontal an angle that will be used to determine the orientation of the neck (fig.6).
The length of this segment will be used to determine its size in relation to the rest of the body. Several methods of evaluation of the length of the neck may be offered. We have chosen to keep back the comparison with the length of the thoracolumbar spine, i.e. of the "dorsal segment" that goes from the top of the withers to the croup top (sacroiliac joint) (fig.7)
The objective measurement can be done using a folding ruler and a protractor.
The horse has to be at a standstill, with the front canon bones vertical.
The dimension is measured between the base of the 7th cervical vertebra (an open hand above the tip of the shoulder in the direction of the withers) and neck (the atlas base) and compared, with the distance between the top of the withers to the top of the croup (sacroiliac junction).
The neck plays a role of balance in stretching and in lowering at the time of the bascule of the horse above the fence and rising at the time of landing and the recovery of balance. It is driven by a series of muscles which ensure this role of lever.
The lowering of the neck in the daily training allows elevation of the back and plays an important role in the construction of an appropriate musculature.
Its contraction or his relaxation contributes to facilitate or complicate the interaction between the hand of the rider and the horse's mouth.
Its lateral flexibility is important in the bodybuilding of the back and shoulders and the maintenance of a proper balance on a jumping course.
A long well used neck is an asset in his role as beam but it can become a disability if it is rigid and compromises the dialogue with the horse's mouth.
Conversely a short neck will limit its effectiveness to optimize the trajectory of the jump but less disturb the dialogue with the mouth.
An upward neckline amplifies the role of beam if it is well used but will produce the opposite effect if the rider does not get the horse stretching over the fences and it will then compromise the proper functioning of the back.
A downward neck relieves the back muscles but makes it harder for the rider to get the balance recovery of the horse.
Colonel DESROCHES, Emeritus rider and an admirer of the anglo-arabes said about the neck, that the way in which the horse uses it, is more important than its length or orientation.
We must respect the opinion of this horseman but, so far, avoid extremes.
In terms of length, the best is the enemy of good, and in terms of orientation, the median area is preferred.
We can see again how the quality of a neckline can be rated regarding its interaction with the other parameters of the morphology and locomotion.
A short and horizontal neck makes difficult the correction of the natural balance, especially for horses with a short back, but it becomes less problematic for horses with a good mouth and a good balance.
A long and slightly vertical neck makes difficult to manage the balance of the horse with a long and plunging back, but it can also, if the rider gets the horse to use it properly, compensate for the disadvantages of a short and rigid back.
Other essential interactions between the neck and the other characteristics relate to the form and use of shoulder, the elasticity of the jump and the balance recovery at landing.
Given the important role of the neck and the dangers of the extreme positions, it seems reasonable to recommend to seek to breed horses "in the Middle" with regard to the length and orientation of the neck.
But, not to discourage anyone, think of Baloubet du Rouet and its vertical neck, Uriel offspings and their short necklines of Hickstead and his rather horizontal neckline and agree that again, nothing is absolutely crippling.