PARASITES AXD PARASITIC DISEASES OF HORSES 



43 



As the average period of incubation on the animal is about 4 days, 

 and the average period after hatching until egg laying begins is 11 

 days, a new generation of mites may be produced in about 15 days. 

 If the first treatment or dipping could be depended on to kill all the 

 mites on the animal the time for the second treatment could be calcu- 

 lated accurately. Unfortunately; the first treatment usually does not 

 kill all the sarcoptic mites on the animal because of the difficulty of 



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-*_-_ __.!_• 



Figure 28. — Sarcoptic mange. Head, neck, and shoulders involved. 



getting the dip or other insecticidal substances into the burrows and 

 in contact with the mites. Practical experience has shown that the 

 interval between treatments or dippings should be from 5 to 7 days. 



Symptoms. — In the early stages of sarcoptic mange in horses the 

 first visible lesions usually occur on the neck or shoulders or around 

 the head, but the disease may start on the breast, flanks, sides, or other 

 parts of the trunk. From these parts the disease spreads until the 

 entire surface of the body may become involved. 



The mites penetrate the upper layer of the skin, each female making 

 a separate burrow or gallery, which usually extends to the sensitive 

 tissues or "quick." The presence and activities of the mites on the 

 sensitive tissues cause great irritation and itching, and the skin be- 

 comes inflamed and swollen, so that small nodules are formed over and 

 around the burrows. As the disease develops vesicles are formed 

 which break and discharge serum. As the serum dries, small scabs 



