LECTURE XXIX 

 NODULE DISEASE OF SHEEP 



General history. — The history of outbreaks is often as fol- 

 lows: Sheep have access during the summer and fall to low 

 pastures or pond or well water that receives drainage from a 

 sheep yard or pasture. Perhaps the grass was short and the flock 

 was compelled to graze very close. During the winter the flock 

 becomes unthrifty; some individuals grow thinner and weaker 

 and a number die. A dead sheep is opened and the intestines 

 show on the surface a large number of nodules about the size 

 of garden peas, which are most common on the large intestine. 

 As soon as grass comes and the sheep are turned out they begin 

 to do better, and the disease seems to disappear. 



Cause. — The disease is caused by a minute roundworm. Sheep 

 are affected by two species but Oesophagostomum columbiamim 

 is the common species. 1 The adult worms are about three quar- 

 ters of an inch in length and inhabit the intestines. The imma- 

 ture forms vary from one hundredth to one sixth of an inch in 

 length, depending on development, and exist inside of the little 

 nodules which constitute the most prominent features of the 

 disease as seen on examination post mortem. 



There is some question concerning the life history, but the 

 eggs are apparently laid by the adult female in the intestine 

 and as eggs or embryos pass out with manure, hatch outside, 

 and gain entrance as embryos. The embryo worms find their 

 way through the internal lining of the intestine, and locate in 

 the bowel wall. 2 Here they give rise as foreign bodies to the 

 little tumors or nodules, about the size of a pea, which nature 

 throws around them, evidently in an attempt to fence them in. 

 They cause irritation as foreign bodies, and this irritation will 

 account for the little tumors which are found on the side of the 



1 Cattle and hogs have each one species of nodule worm which does not 

 affect sheep. In these the loss is unimportant. 



2 Dimock has found evidence which indicates that the eggs may be de- 

 posited within the intestinal mucous membrane and there hatch the em- 

 bryo worms. 



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