EFFECTS OF INBREEDING ON FECUNDITY 7 



ment but the second generation was scarcely equal to the inbreds. A high 

 variability in proportion of daughters free from winter pause occurred in the 

 checks, probably due to environmental factors. In general, the proportion of 

 females with winter pause does increase immediately with inbreeding and this 

 increase is maintained by continued inbreeding. 



High intensity showed neither an increase nor decrease under continued in- 

 breeding. As compared with the check group and the first generation of inbred 

 lines crossed, the inbred daughters were significantly lower in intensity. The 

 data show that the first generation of inbred daughters exhibited very low in- 

 tensity which was maintained through four generations. 



There were no recognizable effects of inbreeding on the proportion of non- 

 broody daughters produced, as shown by a comparison of inbreds with checks. 

 This result might have been anticipated in a flock which is made up largely of 

 non-broody individuals. 



A cumulative effect of continued inbreeding on persistency was observed. 

 The first generation inbred daughters showed about 53 per cent genetically 

 highly persistent. In the third generation only 42.5 per cent were persistent. 

 In the third generation only 12.5 per cent were persistent and in the fourth gen- 

 eration all daughters died before completing their laying year. Crossing inbred 

 lines stimulated persistency to some extent. 



Pullet-year hatching records were obtained on part of each generation of 

 daughters, but the data are too inadequate to furnish much evidence on the 

 relation between inbreeding and hatchability. They indicate, however, that 

 inbreeding immediately lowers hatchability and the effect of inbreeding on 

 hatchability appears to be cumulative. Crossing inbred lines resulted in a 

 decided increase in the proportion of pullets hatching 85 per cent or more of 

 fertile eggs. 



Mean egg weight to January 1 tends to run heavier in the inbred daughters 

 than in the checks. This difference is in part genetic and in part due to the 

 greater age of inbreds when they lay their first egg. The first cross of inbred 

 lines gave a still greater increase in egg size. 



The first generation of inbred daughters gave a mean annual egg record of 

 172.29. The second generation showed about the same mean production, but 

 the third generation fell to 154 eggs. In the fourth generation all pullets died 

 before the end of their laying year. The check daughters sired by the same male 

 as the inbred daughters showed a consistent increase in annual production as the 

 experiment progressed, reaching a mean of about 228 eggs in 1931. Daughters 

 from crossing inbred lines A and C gave higher annual egg records than any 

 generation of inbred daughters. In this experiment inbreeding significantly 

 reduced egg production in the first generation and in later generations. 



The coefficients of variation in annual egg production show no reduction in 

 variability that may be credited to inbreeding. No significant differences of 

 variability between checks and inbreds is apparent. The apparent low variability 

 from crossing the inbred lines in 1932 is not significantly lower than the other 

 constants as judged by its probable error, due to small numbers of birds. There 

 is, therefore, no evidence in these studies to indicate that inbreeding is effective 

 in reducing variation in annual egg production. 



The last column of Table 2 records the laying-house mortality of daughters 

 for a 365-day period from date of housing. The mortality rate for inbred daugh- 

 ters had an upward trend during the experiment and all daughters of the last 

 inbred generation died before the end of the year. Mortality rate was also 

 excessive when the inbred lines were crossed. Inbreeding very definitely in- 

 creased the mortality rate in the laying house in this experiment. 



