488 TYPES AND MARKET CLASSES OF LIVE STOCK 



the bone in turn is supported by the flexor tendon of the foot. 

 (See Fig. 115.) Such defects as an insufficient plantar cushion, 

 a small frog, and contracted feet predispose the horse to navicu- 

 lar disease. In this way the disease may be hereditary, as these 

 predisposing causes may be transmitted to offspring. High 

 knee action, fast work, and hard pavements also endanger a 

 horse from this disease. Dry stables, heavy pulling, and bad 

 shoeing also tend toward the development of this trouble. In 

 the early stages of navicular disease, the animal at rest points 

 the affected foot forward and rests it on the toe, with the fetlock 

 and knee flexed. In the lameness which develops, the affected 

 leg takes a short stride, and the toe strikes the ground first. 

 The disease is progressive and incurable, rendering the animal 

 practically valueless, but not entirely useless on soft ground. 

 To relieve the pain, neurotomy may be performed, an operation 

 in which the sense of feeling is destroyed in the foot by cutting 

 out pieces of the nerve at the fetlock. Navicular disease is one 

 of the most serious unsoundnesses. 



Periodic ophthalmia or moon blindness. This is a disease 

 affecting the eyes of horses, probably caused by a germ. It is 

 quite commonly called moonblindness, because it was thought 

 at one time that the moon had some influence on the cause of 

 the disease. There is undoubtedly an hereditary predisposition 

 to the disease, but there are few cases to indicate that the disease 

 itself is transmitted from parent to offspring, but rather the foal 

 is born with a weakness of the eyes, transmitted by the stallion 

 or dam. Other predisposing factors are low, swampy pastures, 

 poorly ventilated or insufficiently lighted stables, over-feeding, 

 etc. 



The disease comes on with an inflammation usually of one 

 eye. The transparent portion of the eyeball becomes bluish 

 or white in color, most noticeable in the lower part. The eye 

 is kept half closed on account of pain produced by light. Often 

 this is associated by a swelling of the eyelids and reddening of 

 the membrane lining them, with a discharge of tears over the 

 face. There is no indication of an injury or more severe in- 

 flammation at one point than at another. In one to two weeks 

 these .symptoms disappear and the eye may be practically nor- 

 mal to all general appearances for a period of usually one to 

 three months, when another attack occurs more severe than 

 the first. After a few attacks have come and gone, the eye has 

 a bluish appearance, looks cloudy instead of clear, the eyeball is 



