SIDEBONE.

Otago Witness, Issue 3003, 4 October 1911, Page 18

SIDEBONE.

A. A. Johnson, F.R.C.V.S., in the Journal of Department of Agriculture. The question o? dealing effectively with the existence of "hereditary unsoundness ; in draught-horse breeding' stock is receiving considerable attention in New Zealand at ; the present time, and necessarily eo. The profitable trad3 in the export of draught horses to Australia which has • undergone so great a development'with;*', the last two years has served" to emphasise the necessity for. dealing with this matter', seeing that the voluntary system of examinapassed as free from hereditary unsoundness established by " the Australian State Governments has rendered the sale of an uncertificated stallion a matter of difficulty. Further, it is necessary that a stallion be passed as free fro- mhereditary unsoundness before he can bo given any prize in the idiow-ringi so far as thdise shows receiving n, Government subsidy axe,concerned. Now, the most noticeable defect in New Zealand horses, and,for which the greatest number have been rejected by the examining veterinarians in this country, ha© been the condition knOwn as "sidebone"; and, as on many farms where horses are. bred I have found very considerable ignorance existing as to the nature of this condition, and inability to detect very obvious sidebones even when complicated with ringbone and causing lameness, I am hoping that this short description of the nature and effects of sidebone may assist some breeders in detecting this condition, and prove of some value to farmers generally. The foot of the horse is beautifully constructed, so as to present the greatest amount of resistance to concussion within .the smallest space, and thus prevent injurious effects resulting through the weight of the horse's 'body suddenly coming upon one limb and' foot; indeed, continuous progression .on hard roads would be next to imEossible if Nature bad not provided the orse with yielding structures such as are contained within the hoof. Within the horny box we call the hoof are exhibited the pedal bone, the navicular bone, and above these the coronet bone, all of which are held in position by one of the large flexor . tendons forming a ' yielding joint that' distributes t*e weight. The pedal bone is also supported by the horny sole, and the sensitive covering of ike bone at the front and'sides is beautifully dovetailed into and between the corresponding leaves of the horny, box or hoof, which number some 500 or 600; this arrangement again giving a union of strength between sensitive and horny leaves or lamina?: also, the fibro fatty frog at the posterior part of the foot again rests upon the horny frog, of an india-rubber-like nature, that again distributes weight and acts as a sort of buffer. Looking at the 'horse's foot and the inflexion of the horn at the heels to form the bars, one can deduce the fact that the prehistoric horse's foot was -a complete ring of horn, but as the evolution of the animal progressed the faster-wearing parts required a further provision against concussion, arid the posterior rim consequently became inflected to form the bars, the frog becoming developed into its present form. Attached to the posterior portion of the pedal bone both inside and outside is a curved plate of cartilage (gristle) known as the lateral cartilage; it is' so extensive that it extends above the margin of. the hoof in art upward direction as far forward as the cornet, and as far back as the heels. There is no other structure to which these cartilages can be compared, and they are quite peculiar to the equine foot; What purpose do they serve? and why is their flexibility so essential? I have previously pointed out that the odd sensitive and horny laminae distribute the weight of the animal. These laminae at the toe are attached to the pedal bone itself, and at Hie heel they cover these cartilages. Half the attachment, roughly speaking, is osseous (bony), and half is cartilaginous (gristly), and the cartilaginous attachment is situated at the posterior portion ef the hoof, the part that comes first to the ground, and is, or should be, a movable, yielding attachment that carries the_ sensitive leaves outwards when the posterior part of the foot descend? under the weight that is placed upon it. They are also an aid to circulation, and act in this wise: they are surrounded by a mass of blood-vessels, a network of veins, and their elasticity and consequent movement assists in forcing along the blood from the valveless veins of the foot towards the limb. There is always some" movement of the horse even when apparently standing motionless, and the slightest change of distribution of weight on the feet, backward or f>wward causes a corresponding tremor of the lateral cartilages, and thereby give assistance to the'-circulation in the coronary vessels of the foot. In a {healthy state the cartilages shciikl be "quite flexible. Pressing on bhen-i with the forefinger or thumb, they shoa'a be capable of distinct ieotc-

] ment, and movable easily under the skin when the foot is held up and the parts I manipulated. When sidebone exists the ! cartilage has become converted into bone, its elasticity is lost,, and it has become .hard, rigid,' and unyielding. Hence, inflexibility of these cartilages, a distinct I hard, bony sensation when pressing on i them just above the hoof towards the back ' of the wall at its upper margin, either j inside or outside, denotes the existence of 1 sidebone, and "when they become bony and | rigid, the -soft, sensitive tissue (the laminae) becomes, as it were, unduly j squeezed at each movement' of progression ! between the horn of the wall of the hoof 1 on the one side and the pedal bone on the ! other,, instead of being prevented from 'suffering undue pressure, as is the case when. the caa-tilages are flexible. Statistics and experience of many years ! recorded m different countries of the world ' have shown that a strong tendency towards this alteration of cartilage into bone is : hereditary. Every breeder, ' - therefore, ' should do- his best to abstain from 'breeding from any mare or stallion that is the subject of sidebone, so that in the course j of time a race of horses may be developed 1 in New Zealand that will be practically exempt from hereditary sidebone, and perhaps on this account alone, other things being equal, be demanded by other less- . favoured countries. I ,