MORTALITY STUDIES IN RHODE ISLAND REDS IP 



By F. A. Hays 

 Research Professor of Poultry Husbandry 



Many attempts have been made to study the part played by heredity in con- 

 trolling the mortality rate in chickens. Most studies have suggested that selective 

 breeding offers possibilities for reducing mortality rate from all causes at dif- 

 ferent ages. A review of previous work was included in the first report of this 

 series and need not be repeated.^ 



From an economic standpoint, mortality rate is very important. With con- 

 stantly improved methods of feeding and management, heavy losses still persist 

 in many flocks and the gross losses from all causes are enormous. Genetic prin- 

 ciples are being applied more and more in poultry breeding, and the accomplish- 

 ment as far as fecundity is concerned is very gratifying. Any information that 

 the science of genetics may furnish with regard to the mortality problem will 

 be highly valuable. 



MATERIALS AND METHODS 



The plan of matings was changed in 1943 so that three generations from 1943 

 to 1945 were produced largely by half-brother-sister matings and a few full- 

 brother-sister matings. The low-mortality line was reproduced by yearling sires 

 and dams and the high-mortality line from cockerels and pullets only. All birds 

 were Rhode Island Reds, and the sole basis of selecting breeders was the family 

 mortality rate. All offspring was carried until eighteen months of age and mor- 

 tality rates from all causes were recorded for three periods: the first eight weeks, 

 from tight weeks to six months, and a full year in the laying houses. The control 

 line was bred especially' for high fecundity without inbreeding and with some 

 attention given to mortality rate. Stock of all lines was reared and housed to- 

 gether. 



Consideration is given first to mortality rates in the three lines for the different 

 periods. This is followed by a study of the causes of mortality as determined 

 through the cooperation of the Department of Veterinary Science. 



MORTALITY RATES 

 The First Eight Weeks 



Since the sexes were not separated until the birds were eight weeks old, the 

 mortality rates for this period include both sexes. In the first generation the 

 mortality rate for the low-mortality line was extremely small, being less than 1 

 percent. At the same time mortality rate in the high line was 36.5 percent, and 

 in the controls 7.4 percent. 



In the second generation there was very high mortality in the high line, and 

 the low line showed a death rate almost double that of the controls. 



The third generation exhibited a mortality rate of 50 percent for the high line. 

 The low line increased to 16.7 percent mortality, which was nearly double the 

 rate for the controls. 



^This is a cooperative project financed in part by the Regional Poultry Laboratory. 

 ^Hays, F. A., 1944. Mortality studies in Rhode Island Reds. Mass. Agr. Expt. Sta. Bui. 420 



