EFFECTS OF INBREEDING ON FECUNDITY 5 



percentage of inbred mothers that met the standard for early maturity fell as 

 low as 53.85 per cent in 1932. When inbred lines were crossed, all of the mothers 

 selected were genetically early maturing. The check mothers showed early 

 maturity consistently throughout the period. 



Weight at first egg is almost entirely dependent upon age at first egg in Rhode 

 Island Reds, as Hays (1933a) has shown. This relation apparently did not hold 

 true when inbreeding was practiced, using 5 pounds as a minimum weight. For 

 example, all the inbred mothers used in 1932 qualified, while in 1933 only one- 

 third of the mothers attained a 5-pound weight at first egg, which indicates that 

 inbreeding did tend to decrease body weight. Crossing inbred lines A and C 

 resulted in a return to satisfactory body weight. The check group of mothers 

 showed satisfactory body weight throughout the experiment. 



A cessation of egg production exceeding four days between November 1 and 

 March 1 was considered a winter pause. The data show no consistent relation 

 between inbreeding and the percentage of birds with winter pause. The check 

 group of mothers was more satisfactory than the inbreds, but these failed to 

 qualify as a whole for absence of pause in three years of the experiment. In 

 general, inbreeding did not appear to greatly affect the proportion of birds with 

 winter pause. 



Highly intense birds will show a mean winter clutch size of 2.6 or more, accord- 

 ing to previous studies on this flock (Hays and Sanborn 1927). The data presented 

 in Table 1 show a progressive decrease in intensity of the inbred mothers through- 

 out the experiment, while the intensity of the check mothers remained at a 

 rather constant level. Crossing inbred lines A and C restored intensity to the 

 original level of the foundation females. These results indicate clearly that 

 inbreeding does reduce intensity of laying. 



The failure of the broody instinct to appear during the first laying year in- 

 dicates a low degree of broodiness, but is not a safe criterion of its absence, as 

 Hays (1933b) showed. Since most of the birds in this experiment were retained 

 for only one laying year, it was possible to employ only this partial criterion of 

 the presence or absence of the broody instinct. Individuals that went broody 

 the first year were known to carry the two complementary genes for broodiness 

 and were selected against. The standard called for no broodiness in the pullet 

 year, and the character of both the inbred and the check mothers remained 

 rather stable in this respect throughout the experiment. 



The proportion of highly persistent mothers had a marked falling off toward 

 the end of the experiment in the inbred lines. Crossing two inbred lines failed 

 to restore persistency to the level of the foundation females. The check females 

 were satisfactory through the five years, except in the concluding year. There 

 is no explanation for the inferior character of the check females of the last genera- 

 tion, other than mere chance. The data in general show a downward trend of 

 persistency following inbreeding. 



The hatchability of the foundation inbred females was unsatisfactory, since 

 only 11.11 per cent gave a record of 85 per cent or more of fertile eggs hatched. 

 This was followed by a still further decline as might be anticipated. In 1931 

 and 1933 none of the breeders qualified in hatchability. Crossing inbred lines 

 did improve the hatchability. The check females were also an inferior lot from 

 the standpoint of hatchability, but there was no significant decline throughout 

 the experiment. There is, in general, a downward trend in hatchability of the 

 inbred females used. 



