INBREEDING IN RELATION TO EGG PRODUCTION 257 



three years. The report is concerned chiefly with characteristics known to 

 affect fecundity. His results indicate that inbreeding did not affect body weight. 

 Both fertility and hatchability showed decUne. There was some evidence of 

 reduced variability in winter egg production under inbreeding. Winter egg 

 production showed a decline after the degree of inbreeding exceeds 25 per cent 

 (Wright, 1922a, Coefficients of inbreeding). 



Goodale (1927) presents data on White Leghorns using brother-sister matings 

 through six generations. His data indicate some retardation in sexual maturity 

 in successive generations. Body weight was not affected. W^inter and annual 

 egg yield also show a very perceptible fall. This investigator suggests the proba- 

 bility that more experience may enable the breeder to maintain brother-sister 

 matings indefinitely. 



Dunn (1927) reports further progress in inbreeding White Leghorns as well 

 as the effects of crossing inbred lines. His results on inbreeding agree with those 

 previously stated. No family has survived beyond the fifth generation of in- 

 breeding. Of the four original families of 1920, only one remained in 1927, and 

 of four families started since 1920 only two now survive. Hatchability declined 

 in six years from 75 per cent to 41.5 per cent for the inbreds, while the controls 

 increased from 49. S per cent to 59.2 per cent. Dunn obtained very marked 

 improvement in hatchability, mortality rate of chicks, body weight and sexual 

 maturity by crossing inbred families. There was also increased winter egg pro- 

 duction over that of inbreds, but these winter egg records were not equal to the 

 records made by the foundation birds when the experiment began. 



Experimental evidence, therefore, does not indicate that close inbreeding of 

 fowls of a pure variety and from a restricted ancestral foundation is to be recom- 

 mended in breeding for egg production. 



Experiment at the Massachusetts Agricultural Experiment Station 



The experiment reported here was begun in 1923 and closed in 1929. The fowls 

 used were Rhode Island Reds bred for high fecundity since 1913. No outside 

 stock was introduced between 1916 and 1923, but the foundation birds of the 

 flock came from several rather diverse sources. Inbreeding was not practiced 

 in developing the flock for high fecundity, but a considerable proportion of com- 

 mon blood had accumulated in the 10-year period so that the flock is rather 

 closely bred. 



Objects of the Experiment 



The chief object of this experiment was to study the effects of different degrees 

 of inbreeding upon characteristics affecting egg production in Rhode Island 

 Reds and to further study the effects of heterosis on fecundity traits. 



Plan of Experime7it 



A group of intensely inbred hens was mated to an outside male of "Standard" 

 breeding to study effects of heterosis. 



The check group included various degrees of heterosis (Group 1, 2 and 3) 

 for the first three years, and for the last three years the checks were inbred. 



Inbred groups began with four different degrees of inbreeding to found groups 

 4, 5, 6 and 7, and the inbred Hnes were crossed during the last three years of the 

 experiment. 



This experiment was planned to demonstrate: First, the effects of crossing a 

 "Standard"-bred male upon intensely inbred hens from the production-bred 

 flock; second, the effects of different degrees of inbreeding upon fecundity traits; 

 third, the effects of inbreeding the outbred check group; fourth, the results from 

 crossing the different inbred lines. 



