Page 1078 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Nervous system 1053

VetBooks.ir exaggerated movement or range of motion, is recog- abnormal positions when asked to stop quickly after
a few circles in walk.
nised as over-reaching and is prominent in cerebellar
disease. After the horse has been examined walking
At the walk, the horse should be asked to under-
in a straight line, additional more challenging tasks take a number of tasks including walking backwards,
can be introduced. First, the horse should be walked in a tight serpentine and up and down a kerb-stone.
in a straight line with the head elevated. Sometimes A normal horse should be capable of backing-up
horses with proprioceptive deficits will ‘float’ their easily and moving diagonal fore- and hindlimbs
forelimbs at the end of the protracted phase of the together in a rhythmical way, and without making
stride. Next, pulling on the tail while the horse is a mistake or tripping on themselves. Horses with
moving assesses UMN integrity (Fig. 10.11). If the substantial proprioceptive deficits will not be able to
horse can be pulled to one side it suggests that the protract either hindlimb when asked to back-up, and
appropriate extensor muscles have not been initi- may even collapse. Asking a horse to walk in a tight
ated to counteract the pull on the tail. This could be serpentine may show an abnormal sway of the pelvis,
due to a lesion between the UMN cell bodies in the or the horse may step on themselves in an unpre-
brainstem and the LMN supplying the hindlimbs. dictable way, both of which are signs of hindlimb
Horses with weakness due to LMN lesions such as proprioceptive deficits. Similarly, horses with these
botulism may have a weak tail pull response, but deficits may also stumble up and down kerb-stones.
not usually to the degree of a horse with a recent Repeating walking exercises while the horse is
compressive spinal cord lesion. Botulism cases will blindfolded can help to exacerbate low-grade neuro-
usually have other signs of generalised weakness in logical deficits. Some horses with general proprio-
addition to a weak tail pull response. ceptive deficits may be markedly abnormal without
Next the horse is turned in small circles: the han- visual clues, and the handler should always be pre-
dler leaves the horse’s head on a relatively free rein pared to remove the blindfold if the horse appears
and walks towards the pelvis, encouraging the horse
to turn tightly with them. A lack of general proprio-
ception results in poor coordination during move- 10.12
ment. This shows up as wide circumduction of the
outside hindlimb when turned in a circle. A horse
with forelimb proprioceptive deficits may pivot on
the forelimb when turning tightly, rather than step-
ping over and crossing the forelimbs (Fig. 10.12).
Additionally, ataxic horses may leave limbs in

10.11

Fig. 10.12 Ataxia
secondary to proprio-
ceptive deficits in both
forelimbs. This animal
was diagnosed with
Fig. 10.11 Tail pull to assess weakness in the cervical vertebral com-
hindlimbs. pressive myelopathy.