or the presence of spavin in a large percentage of
the progeny of sires so affected. This fact has been repeatedly
demonstrated in this country as well as elsewhere according to Quitman,
Dalrymple and Merillat.[51] A number of states have passed stallion
inspection laws stipulating that animals having such exostoses as spavin
and ringbone cannot be registered except as "unsound."

Asymmetrical conformation, particularly where the hock is obviously
small and weak as compared with other parts of the leg, constitutes a
noteworthy predisposing cause.

Peters' theory is plausible that the screw-like joint between the tibia
and the tibial tarsal (astragulus) bones causes these structures to
functionate in a manner not in harmony with the provisions allowed by
the collateral ligaments of the tarsus, permitting movement only in a
direction parallel with the long axis of the body.

Because of the quality of their temperaments, nervous animals possessing
no particular congenital structural defects of the hock and having no
history of spavined progenitors, are subject to spavin when kept at work
likely to produce tarsal sprain. Spavin usually develops early in such
subjects and examples of this kind may be frequently observed in
agricultural sections of the country. Where spavin develops in unshod
colts at three and four years of age, shoeing is not an influencing
agency when animals are not worked on pavements.

Exciting causes of spavin are sprain and concussion. Various hypotheses
are recorded as to how sprains are influenced and among others may be
mentioned that of McDonough[52], which is that the foot is robbed of its
normal manner of support by the ordinary three-calked shoe. With such a
shoe, little support is given the sides of the foot; hence, undue strain
is put upon the collateral ligaments of the tarsus. Moreover, the shoe
with its calks increases the length of the leg and adds to the leverage
on the hock, by virtue of such added length. This makes for greater
strain upon the mesial or lateral tarsal ligaments whenever the foot
bears upon a sloping ground surface, so that one side (inner or outer)
is higher or lower than the other. But according to McDonough's theory
(a good one concerning horses that work on pavements), the chief error
in shoeing lies in that the foot is deprived of its normal base or
support on the sides--the three-calked shoe being an unstable
support--and that this manner of shoeing city horses