12 



MASS. EXPERIMENT STATION BULLETIN No. 284 



Losses Due to PuUorum Disease 



27. — Do adult flocks suffer a mortality from this disease? Yes. Occa- 

 sionally a hijfh mortality may be experienced when the disease develops into an 

 acute form. Carriers in general do not possess the disease resistance of normal 

 birds; therefore, a higher mortality is observed among carriers than among 

 healthy individuals. 



28. — Is egg production affected? Yes. Investigations have shown that 

 infected birds do not lay as well as non-infected birds. This may be accounted 

 for by the diseased ovary, underdevelopment, and low disease resistance of the 

 bird. 



29. — Are fertility and hatchability affected? \ Cs. The percentages 

 of fertility and hatchability are markedly reduced. 



30. — Do chicks suffer a mortality? Frequently high mortalities, sometimes 

 as high as 100 per cent, are observed among infected chicks and infrequently 

 little if any mortality is observed. Overheating, chilling, overcrowding, and 

 insanitarv conditions markedly influence the mortalitv rates. 



Photograph 11. — Dead Embryos. 

 Pullorum disease affects hatchability. At the end of the incubation period, embryos 

 may either be dead in the shell or be too weak to emerge from the shell. Embryos IV 

 and V were removed from the shell on the twenty-first day of incubation. S. pullorum 

 was isolated from embryos III. IV. and V. Pullorum disease should not, however, be re- 

 garded as the only cause responsible for low hatchability. Refer to question 29. 



