118 



Hereditary Diseases of Horses^ 



stances, been very evident in the third generation. Some time 

 ago, a friend of my own got from Northumberland two young 

 horses of considerable value. Though perfectly sound at the 

 time of purchase, both soon after became roarers : they had been 

 bought from different breeders, but, on inquiry, it was found 

 that both were got by the same sire, and that many more of his 

 progeny had also become affected by the same disease. 



But roaring may occur independently of hereditary causes. 

 It is occasionally produced by the presence of tumours in the 

 larynx or trachea ; more often by constrained positions of the 

 head and tight reining, and hence frequently occurs in old 

 carriage-horses. It is sometimes met with in crib-biters, from 

 their being made to wear straps buckled too tightly round the 

 throat. It supervenes from bad attacks of bronchitis, especially 

 when of frequent occurrence, and also from phlebitis, being 

 caused in the latter instance by defective nutrition of the 

 muscles of the larynx. But even in cases where roaring is 

 not congenital, but is produced during the lifetime of the 

 animal, and by accidental causes, it may manifest a hereditary 

 tendency. There is, indeed, no accidental defect more com- 

 monly transmitted from parent to offspring than that on which 

 roaring depends. 



Considerable caution is requisite in judging as to the existence 

 of roaring in stallions of the heavier breeds, for three-fourths of 

 these, when briskly exercised, produce a loud roaring noise, which 

 often occurs without any disease of the larynx, trachea, or any 

 part of the respiratory apparatus. It results from the high spirit 

 and condition in which entire horses are usually kept, from the 

 acute angle at which they generally carry the head, the abundant 

 deposition of cellular tissue and fat about the throat, the com- 

 paratively small width between the sides of the lower jaw, the 

 great development of the muscles of the neck, and the thickness 

 of the mucous membrane lining the larynx and contiguous parts. 

 But the noise so produced is somewhat different from that 

 depending upon morbid peculiarities. It is observed during 

 expiration as well as inspiration, and usually disappears when 

 the nose is elevated so as to be placed as much as possible in a 

 line with the neck. When the sound has these distinguishing 

 characters, and occurs in animals of the heavier breeds with 

 well-formed necks and chests, it is not likely to be productive 

 of any bad effects, or to be hereditary. All such sounds occur- 

 ring in the lighter breeds of horses must, howev-er, be regarded 

 with great suspicion. 



There are few diseases in which hereditary tendencies are so 

 manifest as in that variety of deep-seated ophthalmia, or inflam- 

 mation of the eye, recognised by veterinarians under the various 



