unthinkingly returning such birds without determining their health status. 

 Some breeders follow the preferred policy of not returning such birds to the 

 flock, in order to avoid the possibility of introducing diseases into the flock. 

 In Flock 5 the explanation for infection might be the introduction of males 

 from an unknown source. However, it is questionable whether or not infected 

 males could bring about 11.65 percent infection in a flock. It is likely that 

 some other factors also were operative in bringing about infection. 



While the percentage (2.94) of "breaks" may appear small, it nevertheless 

 constitutes a problem to the poultry industry. This is especially true as long 

 as poultrymen are willing to tolerate the existence of scattered foci of infection 

 within the State, to permit the importation of infected stock, and to neglect 

 to carry out effective preventive measures against the introduction of the 

 disease into the flock. 



Table 3. Appearance of Infection in Flocks Previously Negative 



1936-37 Season 



11.65 Introduced males fr 



known source 



6,214 6,214 0.40 No definite source 



6,214 *2,736 0.00 



* Represents retests. 

 ** Reactors the previous season but cleaned up infection by retesting. 



Non-Reacting and Positive Flocks Classified by Counties 



Table 4 shows that during the 1936-37 testing season, 281 non-reacting 

 flocks, representing 424,431 birds, were detected. The number of birds in 

 the non-reacting flocks represented 94.6 percent of the total birds tested. 

 The number of 100 percent tested, non-reacting flocks was 233. The number 

 of birds. in these flocks, representing 84.4 percent of the total tested, was 

 378,563. Norfolk, Middlesex and Worcester Counties have the largest number 

 of birds in non-reacting flocks. 



Twenty-six flocks, representing 24,088 birds, were classified as infected. 

 Only 5.4 percent of the total birds tested were in positive flocks. 



The data in Table 4 show that Massachusetts is constantly progressing in 

 establishing and maintaining pullorum-clean flocks. The industry should rec- 

 ognize its puUorum-disease-free flocks and utilize these sources to a greater 



(6) 



