392 MANAGEMENT AND FEEDING OF SHEEP 



an emaciated condition, a pale skin, a dry harsh coat, a 

 moping gait and diarrhea. One of the surest evidences, 

 however, when it is present, is the small white worm in 

 the droppings. Usually no positive symptoms occur un- 

 til after the lambs have been affected for some time. 

 When death occurs, it is generally soon after the symp- 

 toms have become prominent. The trouble affects old 

 sheep as well, but they are much less harmed than lambs 

 by the presence of the worms. Death from this source 

 occurs mainly among lambs that have access to pastures 

 at a somewhat early age. 



The life history of the stomach worm is in outline as 

 follows : The worms occur in largest numbers in the 

 fourth stomach of the sheep. In the adult sexual stage 

 they are able to live and carry out their reproductive 

 functions only in the alimentary canal of sheep and some 

 other ruminants. Each female produces thousands of 

 eggs very diminutive in size. They pass out of the in- 

 testines with the feces. In a few hours, days or weeks, 

 according to the temperature, they hatch out, if not killed 

 by drying or freezing. The tiny embryonic worms then 

 develop to what may be termed the final larval or infec- 

 tious stage. This period of development requires days or 

 weeks, according to the temperature. In the infectious 

 stage they can withstand long periods of drought and 

 cold. When in that stage they are most active in the 

 presence of moisture, as during wet weather or when 

 dews and fogs abound they crawl up grass blades and 

 thus readily reach the stomach of sheep and lambs. In 

 some instances they must develop very quickly, as they 

 are found in lambs in immense numbers that are less than 

 three months old. 



This theory of the source and manner of infection 

 finds support in experiments conducted by the author at 

 the Minnesota station. When the lambs were confined 

 to the sheds and fed on soiling foods to supplement the 

 milk of the dams, they were free from attack ; whereas the 



