MORTALITY STUDIES IN R. I. REDS II 3 



In general, the data show a significant difference in mortality rates between 

 the high and the low line. There was also a significant increase in mortality in 

 both the high and the low lines through three generations. In the second and 

 third generations mortality was significantly higher in the low line than in the 

 controls. This fact suggests a lack of progressive reduction in mortality in the 

 low line. The line selectively bred for low mortality was not equal to the con- 

 trols after the first generation. 



From Eight Weeks to Six Months of Age 



During this period the sexes were carried separately on good grass range. 

 Complete families of males and females were retained in the high and low lines. 

 In the control line, complete families of females were retained but only partial 

 families of males. 



In the high line, mortality among the males amounted to 44.1 percent in the 

 first generation, increased to 62.9 percent in the second generation, and fell to 

 20.0 percent in the third. There was a highly significant difference in mortality 

 rates between the high and low lines. Males in the low line compared favorably 

 with the controls in the three generations. A lack of progressive decrease in mor- 

 tality was noted in the low line. 



Females of all three lines had a very low mortality rate in the first generation. 

 In the second generation female mortality rose to 52.5 percent in the high line 

 but remained low in both other lines. In the third generation mortalky remained 

 high in the high line, and showed an increase in the control and low lines. There 

 appeared to be a significant difference in mortality of females in the high and the 

 low lines. 



From Six to Eighteen Months of Age 



During the period of one year in the laying houses, males of the high and low 

 lines exhibited a significant difference in mortality rates. Mortality in the low 

 line was higher than in the controls. For the three generations there was no 

 increase in mortality in the control line. 



For the first year in the laying houses, pullets of the high and low lines were 

 not consistently different in mortality rate. This variability may have been due 

 in part to small numbers. Neither of the selected lines was as good as the con- 

 trols. Small numbers of both males and females in the two selected lines were 

 caused by low hatchability and high mortality up to the age of six months. 



The means of three generations, given at the bottom of the table, appear to 

 suggest two possibilities: first, that selective breeding for high and low mortality 

 does result in a very significant difference in mortality in the two lines; and second, 

 that selective breeding for low mortality did not produce a line superior to the 

 controls, which were bred for high fecundity characters. 



The annual egg records are given in the last column of Table 1. The small 

 number of normal egg records for the high-mortality line is very evident. There 

 was a pronounced decline in annual egg production during the three generations. 

 The low-mortality line, however, did not decline in egg production after the first 

 generation, but the limited data indicate that they failed to maintain a satis- 

 factory production level. The control line maintained a high level of production 

 throughout the experimental period. 



