INBREEDING IN RELATION TO EGG PRODUCTION 299 



In chart 7 the inbred mothers having daughters were superior in annual egg 

 production to the check mothers. Original inbred mothers showed a mean an- 

 nual egg record of 238, compared with the original check mothers whose average 

 was 194 eggs. The same relationship holds for the two groups up to 1928 when 

 the mean egg record for inbred mothers was 201 and for check mothers 203. 



The first group of inbred daughters hatched in 1923 showed a mean record of 

 219 eggs. Inbred daughters of 1924 gave a mean egg record of 170, and the in- 

 bred daughters of 1925 laid 159 eggs. Check daughters of 1923 averaged 146 

 eggs, those of 1924 averaged 204 eggs, while those of 1925 fell to 159 eggs. Com- 

 pared with the check groups, inbreeding did not affect annual egg yield. On 

 the basis of absolute values, however, the inbred daughters exhibited a marked 

 and consistent decline as inbreeding progressed. On the other hand, the check 

 daughters exhibited an upward trend in egg yield as the experiment progressed. 

 On the whole, the data show that fecundity, as measured by annual egg yield, 

 decHned consistently in the three years of inbreeding. 



For 1926 and 1927 when checks were inbred and inbred lines were crossed, 

 the check daughters showed no significant change in annual production over the 

 previous three years. Inbred daughters in these two years exhibited an increased 

 production over the previous two years of inbreeding, but did not attain a pro- 

 duction equal to that of the initial flock of inbred daughters. Intercrossing in- 

 bred lines has increased production over that of the second and third years of 

 inbreeding, but the daughters failed to attain the level exhibited by either the 

 foundation females or the first generation of inbred daughters. 



192U 1925 



JIATINO YEARS 

 CHART 8. — Effect of Inbreeding on Hatchability (Per Cent) 



192s 



Chart 8 shows the mean hatchabiUty of dams with daughters throughout the 

 experiment. It will be observed that the mean hatchability of the inbred dams 

 in 1923 was 79 per cent. In 1924 the mean fell to 62 per cent, and in 1925 rose 

 again to 77 per cent. Check mothers showed a mean hatchability of 72 per cent 

 in 1923, 36 per cent in 1924 and 67 per cent in 1925. Inbreeding has apparently 

 not affected hatchability the first three years. 



Inbred strains when crossbred in 1926 gave the same mean hatchability, 

 namely, 78 per cent, that was obtained during the last year of inbreeding, but 

 the figure dropped to 50 per cent in 1927. In 1928, the mean hatchabihty of 

 inbreds closely approached the original level of 79 per cent. Check females 

 exhibited no change in hatching record in 1926 when inbred, and their hatchability 

 slowly increased later to the same figure as shown by the inbreds, namely, 77 



