VIGOR IN PRODUCTION-BRED FLOCKS 175 



The most potent cause of deaths in the laying houses falls in the unclassi- 

 fied group which may be considered lack of vigor. Roup and "going light" 

 are the most important disorders in the flocks studied. 



In improving a flock for vigor, the most feasible practice consists in breed- 

 ing exclusively from those families showing the very lowest mortality of 

 pullets in the laying houses. 



References 



Bittenbender, H. A. 1922. Breeding Rhode Island Reds for type and egg pro- 

 duction. Iowa Agr. Expt. Sta. Bui. 202. 



Dryden, J. 1921. Egg-laying characteristics of the hen. Oreg. Agr. Expt. Sta. 

 Bui. 180. 



Dunn, L. C. 1922. The relationship between the weight and the hatching qual- 

 ity of eggs. Conn. (Storrs) Agr. Expt. Sta. Bui. 109. 



Dunn, L. C. 1922a. Hatchability and chick mortality. Poultry Sci. I. No. 2. 



Halbersleben, D. L., and F. E. Mussehl. 1922. Relation of egg weight to chick 

 weight at hatching. Poultry Sci. I. No. 4. 



Harris, J. A. 1926. The monthly egg records of birds which die during the 

 first laying year. Poultry Sci. VI. No. 1. 



Harris, J. A. 1927. Further studies of the monthly egg records of birds which 

 die during the first laying year. Poultry Sci. VI. No. 5. 



Hays, F. A. 1924. Inbreeding the Rhode Island Red fow*! with special refer- 

 ence to winter egg production. Amer. Nat. 58:43-59. 



Hays, F. A., Ruby Sanborn and L. L. James. 1924. Correlation studies on 

 winter fecundity. Mass. Agr. Expt. Sta. Bui. 220. 



Hays, F. A., and Ruby Sanborn. 1926a. Broodiness in relation to fecundity in 

 the domestic fowl. Mass. Agr. Expt. Sta. Tech. Bui. 7. 



Hays, F. A., and Ruby Sanborn. 1926b. Annual persistency in relation to 

 winter and annual egg production. Mass. Agr. Expt. Sta. Tech. Bui. 9. 



Hays, F. A., and Ruby Sanborn. 1927. Intensity or rate of laying in relation 

 to fecimdity. Mass. Agr. Expt. Sta. Tech. Bui. 11. 



Hays, F. A., and A. H. Sumbardo. 1927. Physical Character of eggs in rela- 

 tion to 'hatchability. Poultry Sci. VI. No. 4. 



Hays, F. A. 1927. The inheritance of persistency and its relation to fecundity. 

 Proc. World's Poultry Congress. 



Jull, M. A., and S. Haynes. 1925. Shape and weight of eggs in relation to 

 their hatching quality. Jour. Agr. Research XXXI. No. 7. 



Lippincott, W. A. 1921. Poultry production. New York: Lea and Febiger. 



Pearl, R. 1911. Breeding poultry for egg production. Maine Agr. Expt. Sta. 

 Bui. 192. 



Rice, J. E., and H. E. Botsford. 1925. Practical poultry management. New 

 York: John Wiley & Sons, Inc. 



Stewart, J. H., and Horace Atwood. 1909. Some factors influencing the vigor 

 of incubator chickens. W. Va. Agr. Expt. Sta. Bui. 124. > 



\ 



3500-^4-'28. No. 2109 



