lo May, 1910-] Hereditary Unsoundness in Horses. 329 



Commission on horsebreetlinj,', drew up a list of those diseases " which by hereditv 

 rendered stallions unfit as breeding sires," and that in that last list was sidebone. 

 Sidebones therefore are hereditary. 



Axe {The Horse in Health and Disease — ist edition, vol., 6, page 



387): 



Sidebone is one of the most pronounced of hereditary diseases. Its tendency to 

 arise in the progeny of affected animals is now known to every horsebreeder of 

 experience. 



iNIOLLAR AND DoLLAR {The Practice of Veterinary Surgery, page 

 630) : — 



The causes are (i) congenital predisposition, m heavy coarse-bred horses. 



Other pathological conditions constituting unsoundness which are 

 generally regarded as hereditary, are : — 



Ringbone (Exostosis at the distal extremity of the os suifraginis 



and' on the os corona) ; 

 Bone Spavin (Anchylosis with exostosis of the small bones of 



the tarsus — the cunieform parvurn, medium and magnum; 

 Curb (Sprain of the calcaneo-cuboid ligament) ; 

 Roaring (Paralysis wath atrophy of all the intrinsic muscles of 

 larynx on the left side except the orico-thyroideus). 

 The following are also, but less commonly, classed as hereditary un- 

 soundnesses : — 



Bog Spavin (Bursitis with permanent distension of the synovial 



capsule of the tibio-astragalus articulation or true hock joint) > 



Thoroughpin (Bursitis with permanent distension of the sheath 



of the flexor pedis perforans tendon of the hind limb) ; 

 Navicular Disease (Caries of the bursal surface of the os 



naviculare ; 

 Nasal Disease (Osteo-porosis), and 

 Chorea. (''Shivering" or "Nervy.") 

 The remarks made with regard to the absence of definite observations 

 concerning the hereditary character of Sidebone may be even more forcibly 

 applied to all but one (Roaring) of the above-mentioned unsoundness. Con- 

 cerning the others, no exact evidence has ever been recorded to my know- 

 ledge. The following references from standard authors, relating to the 

 more important of the.se unsoundnesses, indicate the usual attitude adopted 

 when discussing their hereditary character. The tendency is for each 

 author to launch an ipse dixit, rather than to furnish proof or refer to 

 evidence : — 



Ringbone 



Williams {Principles and- Practice of Veterinary Surgery) : — 

 Hereditary predisposition is sufficiently proved and acknowledged. I therefore 

 simply advise breeders of horses never to breed from a sire or dam having ringbones. 



GouBAUX AND Barrier {The Exterior of the Horse-French) : — 



The influence of hereditary has been recognised for a long time. Certain families 

 of horses invariably transmit them to their descendants. 



Axe {The Horse in Health and Disease — vol. 5, page 205) : — 

 Horses with upright pasterns, and animals with pasterns of undue length are 

 specially predisposed to it. 



MoLLAR AND DoLLAR {The Practice of Veterinary Surgery, page 



607) :— ... 



The existence of the disease in two or more feet suggests hereditary predisposition, 

 and mav often be traced to small badly-shaped joints or defects in the formation of 

 the limbs. . . . Such conformation, being perpetuated in the progeny, renders 

 it easy to understand why the disease is often inherited. 



