LENGTH OF BIOLOGICAL LAYING YEAR 9 



of 315 to 365 days. Daughters from dams with a biological year greater than 365 

 days show a significantly higher mean annual persistency than do daughters with 

 a shorter biological year. Mean annual first-year egg records of daughters from 

 the three presistency classes of dams increase with the persistency of the dams. 



These data indicate the general superiority of birds with a long biological year 

 over birds with a shorter biological year in breeding for high fecundity. 



The mortality in the laying houses is distinctly higher for the daughters from 

 dams with persistency records below 315 days. The mortality of daughters from 

 dams with persistency between 3L5 and 365 days and from dams with a persis- 

 tency greater than 365 days is essentially the same. These facts indicate that high 

 persistency is a partial measure of vigor which is one of the vital essentials in suc- 

 cessful breeding. 



Progress Throughout the Experiment 

 Chart 1 presents graphically the mean annual persistency of daughters by gener- 

 ations throughout the experiment. Class 1 represents the daughters from dams 

 with a biological year under 315 days; Class 2, the daughters from dams with a 

 biological year of from 315 to 365 days; and Class 3, the daughters from dams with 

 a biological year greater than 365 days. Data are not available for the hatching 

 year of 1919 and 1920. 



■^ 340 



§ 330 



Dame' Biological Class 



Clees 1 



Class 2 



Class 3 



•18 '19 '20 '21 '22 '23 '24 '25 '26 '27 '28 '29 '30 '31 



YEAR HATCHED 



Chart 1. Annual Persistency of Daughters by Years. 



In general, there is a progressive increase in the annual persistency of daughters 

 from year to year. For the most part the daughters from the two classes of dams 

 with superior length of biological \ear excel the daughters from dams with a biolog- 

 ical year under 315 days. There is an apparent advantage from the standnoint 

 of annual persistency in selecting female breeders whose biological year exceeds 

 365 days. The high trend in the solid line in 1928 and 1929 has little significance 

 because it represents the daughters from but four dams in 1928 and one dam in 

 1929. 



Chart 2 presents the mean year'y egg records of daughters from the three classes 

 of dams with respect to length of biological year. Here again there is progressive 

 increase throughout the experiment in daughters of dams that belonged to the 



