MORTALITY STUDIES IN R. I. REDS 19 



SUMMARY 



Records on mortality were secured over an eight-year period on 22,175 chicks 

 up to the age of 8 weeks; on 5,067 males and 9,526 females between the ages of 

 8 weeks and 6 months; and on 1,132 males and 5,803 females between the ages 

 of 6 and 18 months. Available morbid and dead birds were examined by pathol- 

 ogists. The following deductions seem to be warranted: 



1. Selective breeding was not effective in reducing the mortality rate between 

 hatching time and the age of 8 weeks, as shown by the insignificant differences 

 between the lines. 



2. There was a significant increase in mortality rates between the ages of 

 8 weeks and 6 months in the control, the high mortality, and the miscellaneous 

 lines. The low mortality line showed no significant decline during the same 

 period, but there was no increase in mortality rate in this line. 



3. Selective breeding was not decidedly effective in reducing mortality from 

 all causes in males and females between the ages of 6 and 18 months. The con- 

 trol line showed no significant change during the period of observation. The 

 rate of change in both the high and the low mortality lines was insignificant. 

 The miscellaneous group was the only one to show a significant Increase in mor- 

 tality rate. 



4. Necropsy- records demonstrated that the avian leukosis complex showed a 

 cyclic behavior in the eight-year period, and indicate that when the avian leukosis 

 complex appeared In a generation, it was likely to be accompanied by a high 

 incidence of other diseases and disorders. 



5. Digestive disorders appeared prominently In birds examined. 



6. Miscellaneous diseases and disorders, including respiratory diseases, were 

 not prominent in the flock. 



7. Cannibalism was variable and generally more destructive In males than 

 in females, when males that died from fighting are included. 



REFERENCES 



Asmundson, V. S., and Jacob Biely. 1932. Inheritance of resistance to fowl 



paralysis. 1. Differences in susceptibility. Canad. Jour. Res. 6:171-176. 

 Bearse, G. R., and C. F. McClary. 1939. The results of eight years' selection 



for disease resistance and susceptibility in White Leghorns. Rpt. 31st Ann. 



Meeting, Poultry Sci. Assoc, p. 1. 

 Biely, Jacob, Elvira Palmer, and V. S. Asmundson. 1932. II. On a significant 



difference in the Incidence of fowl paralysis In two groups of chicks. Canad. 



Jour. Res. 6:374-380. 

 Bostian, C. H., and R. S. Dearstyne. 1944. The Influence of breeding on the 



livability of poultry. N. C. Agr. Expt. Sta. Tech. Bui. 79. 

 Bryant, R. L., and E. P. Johnson. 1944. Incidence of mortality in two strains 



of Single Comb White Leghorn chickens. Poultry Sci. 23 (6):521-524. 

 DeOme, K. B. 1943. Intraperitoneal Injection of lymphomatous nerve tissue 



into resistant and susceptible chickens. Poultry Sci. 22 (5):381-394. 

 Frateur, J. L. 1924. The hereditary resistance of the fowl to the bacillus of 



diphtheria. Proc. Second World's Poultry Cong. Part 2, pp. 68-71. 

 Gowen, J. W., and M. L. Calhoun. 1943. Factors affecting genetic resistance 



of mice to mouse typhoid. Jour. Infect. Dis. 73:40-56. 

 Hetzer, H. O. 1937. The genetic basis for resistance and susceptibility to 



Salmonella aertrycke in mice. Genetics. 22:264-283. 



