14 FARMERS BULLETIN 713. 



has grown sufficiently to shade the skin and the fleece becomes wet 

 from rain, the disease usually becomes well marked. 



The most important factor in spreading scab infection in the range 

 country is the buck, which is a source of danger too often oA'erlooked. 

 It is the custom in many sections for owners of sheep to put their 

 bucks in a "■ public buck herd." That is, a number of owners all turn 

 their bucks into one herd and a sheep herder takes charge of this 

 community buck herd and iims it on the open range until within a 

 few weeks of the time when the bucfe are to be turned into the ewe 

 flocks. The herd is then split up, each owner taking his bucks home 

 to be fed grain in preparation for the breeding season. These herds 

 usually consist of from 1,200 to 1,500 bucks, representing a large 

 number of owners. Should scab exist in any of the outfits at the 

 time the herd is made up, the entire herd will become infected. In- 

 fection may find its way into the buck herd in a number of different 

 ways, and once introduced the disease will be carried into all of the 

 outfits represented, unless the herd is treated prior to disbandment. 

 It is estimated that more than 90 per cent of the outbreaks of scab 

 in the sheep-growing sections of the West can be traced directly to 

 the public buck herds. All such herds should be dipped just prior 

 to the time the animals are to be distributed to the various owners. 

 This is one of the most important points in eradicating scab from the 

 flocks on the open ranges where this custom prevails. 



One or more attacks of the disease do not confer immunity, and a 

 flock may become infected any number of times. After a flock has 

 been properly treated and the disease cured by dipping, it may be- 

 come reinfected, if exposed by contact with infected animals, bedded 

 down on old infectious bed grounds and corrals, driven on trails or 

 roads over which infected sheep have recently passed, turned on to 

 infectious ranges, pastures, or yards where infected sheep have re- 

 cently been, or in any other manner directly exposed to the infection. 

 As a rule the visible symptoms of reinfection do not appear until 

 after a lapse of 30 days from the date of the last dipping. If condi- 

 tions are favorable and the sheep are thriving, a much longer period 

 may elapse before they show visible symptoms of disease from ex- 

 posure to infection after dipping. The dip that is left in the wool 

 after dipping will often serve, for a limited period of time, as a 

 preventive against reinfection. The length of this period of protec- 

 tion varies with the climatic conditions and the kind of dip used. If 

 the sheep are exposed to frequent, heavy rains after dipping, much 

 of the dip will be washed out of the fleece. A dip containing sulphur 

 acts as the best preventive against reinfection. Tender average con- 

 ditions such a dip will probably afford protection for a period of 

 from 30 to 60 days and, under favorable conditions, for a much 

 longer time. 



