722 
DISEASES OF THE HOCK. 
development of the elements of the joints, especially of its bones and 
ligaments. Working immature animals is also a potent cause. Horses 
which might work quite satisfactorily at five or six years old, not 
unnaturally develop spavin at three or four. 
In considering the question of predisposition, we have to remember 
that the formation of other portions of the limb, and even of the body, 
exercises a considerable influence on the development of the disease. 
Experience shows that uprightness of the fetlock- and stifle- joints 
favours disease, though this formation is often secondary, i.e., a conse¬ 
quence, and not a cause, of the formation of spavin. Kle mm considers 
that animals with cow-hocks, and those which stand with the hind-feet 
far back, are predisposed to the disease, and on this basis explains the 
curative action of shoes with high quarters and deep heels. 
Peters thinks that turned-out hocks are particularly prone to spavin, 
and there is no doubt that this formation interferes with hock action and 
increases the chance of disease. 
Experience also shows that very powerful horses with broad pelves 
and well-developed quarters are particularly liable, the reason being the 
great strain which this formation throws on the hock-joint. The more 
powerful the muscles of the hind-quarter and the freer the movement, 
the greater the strain on the hock. The same is true of over-grown and 
long-backed animals. To produce an equal output of energy, their 
muscles are forced to act more vigorously, and, therefore, greater strain 
is thrown on the hock. For the same reason powerful, spirited horses 
more often suffer than quiet, phlegmatic animals. The fact that spavin 
is commoner in young horses is principally due to the incomplete 
development of then bones and ligaments, and to the existing predis¬ 
position being only brought into play when the young animal is put to 
work ; horses, when once seasoned, not being likely to develop disease 
unless gi eater demands are made on their working powers, or the hock 
is accidentally injured. 
Ihe causa externa is almost exclusively represented by mechanical 
injury. Severe, rapid work, especially under the saddle, or in front of 
heavy loads, often produces slight, frequently repeated strain. Peters 
thinks soft, moist ground and rough pavements particularly injurious, 
because the unavoidable rotary movement of the hoof on the ground is 
interfered witn, and consequently takes place, not at the extremity of 
the limb, but in the joints, especially in the hock-joint. 
Single violent spiains, pioduced, for example, by wheeling round on 
tne hind-quaiteis 01 suddenly throwing the horse on its haunches, may 
determine inflammation of the hock-joint, but this- is far from common. 
Even less frequently is inflammation caused by external injuries, such as 
wounds or bruises. 
