INBREEDING IN RELATION TO EGG PRODUCTION 301 



The mortality records by families of daughters in the laying houses are pre- 

 sented graphically in chart 10. The mortahty for the inbreds was 50 per cent 

 in 1923, 71 per cent in 1924, and 21 per cent in 1925. For the check group, the 

 figures were 48 per cent in 1923, 49 per cent in 1924, and per cent in 1925. 

 There has been a higher death rate in the inbred group for the three-year period; 

 and in 1925, 21 per cent of the inbred daughters died while no check daughters 

 were lost. The absolute mortality rate for the three years showed wide varia- 

 bility, but the close parallelism of the rates for inbreds and checks should be 

 stressed as the only significant item to indicate lower vigor in the inbreds. 



Inbred lines when crossed showed a constant laying-house mortality of 20 to 

 22 per cent. Check groups when inbred showed a mortahty of 45 and 31 per 

 cent for the two years recorded. Since laying-house mortality is one of the 

 most exacting measures of vigor (Hays and Sanborn, 1928), it seems apparent 

 that inbreeding does reduce vigor. 



Summary 



A study of the effects of heterosis over a two-year experimental period is 

 reported. 



The only desirable effect of heterosis observed from the standpoint of fecundity 

 was greater body weight at a given age. The very great danger of failure from 

 the standpoint of high fecundity when outside stock is introduced is clearly 

 illustrated. 



Inbreeding data are presented on mothers and offspring covering a six-year 

 period. The check group was made up from a more diverse ancestry than the 

 inbreds. 



The foundation females in the inbred group consisted of one hen and her daugh- 

 ters. The males used were also related to these females. 



During the first three years of the experiment check groups were made up of 

 different types of outbred and straight Station-bred stock. 



In the first three years the inbred groups represented different degrees of 

 relationship, such as full brother-sister, sire on daughter, mother and son, half 

 brother and sister. 



In the last three years of the experiment, the check groups were closely inbred 

 and the available inbred strains were intercrossed. 



Inbreeding the check groups during the last three years gave results superior 

 to those obtained with the original inbreds during the first three years. This 

 would suggest that birds from a more diverse ancestry may be closely bred with 

 greater safety than those from a very restricted ancestry. 



The data presented do not indicate that sexual maturity was consistently and 

 regularly retarded by inbreeding. 



Body weight at first egg was not affected by inbreeding. 



Winter pause, low intensity and low persistency were probably concomitants 

 of inbreeding. 



Inbreeding tended to lower production. 



Inbreeding decreased fertility. 



Inbreeding probably decreased hatchability. 



Inbreeding tended to lower the sex ratio. 



Inbreeding reduced chick vigor as well as vigor of pullets during their first 

 laying year. 



Uniformity in characteristics affecting fecundity was Uttle affected in the inbred 

 groups from restricted ancestry, but the check birds from more diverse ancestry 

 became more uniform in these characteristics when inbred. 



Inbred strains when intercrossed gave progeny superior to those from the second 

 and third years of inbreeding, but not equal to the foundation stock. 



