6 MASS. EXPERIMENT STATION BULLETIN 312 



In mean egg weight to January 1, there is a significant decline in the inbred 

 females. Crossing two inbred lines restored the winter egg size to its original 

 level. Check females showed an almost constant conformity to the standard 

 for egg size throughout the experiment. Inbreeding seemed to reduce winter 

 egg size in this experiment. 



The annual production of the inbred female breeders began with 231 eggs and 

 showed a consistent decline to 154 eggs. Crossing inbred lines A and C increased 

 the egg production level but not to the original figure. The check female breeders 

 did not decline in production but were rather consistent high producers during 

 the five-year period. Inbreeding did consistently reduce egg production because 

 the selection of breeding females each year was based on anticipated superiority. 



Character of Female Offspring Produced 



All female offspring from the inbred lines, from lines A and C crossed, and 

 from the check matings are classified in Table 2 according to the standard. 

 The three inbred lines are combined. 



The 63 first-generation daughters produced by father x daughter matings 

 showed only about 20 per cent qualifying with a family range mortality to Septem- 

 ber 1 of less than 10 per cent. In the following year the inbred daughters came 

 from half-brother x sister matings in the three lines, and none of these daughters 

 came from families with a range mortality as low as 10 per cent. The third 

 generation of inbred daughters came from one half-brother x sister mating and 

 one full-brother x sister mating. No daughters from the first mating qualified 

 and all daughters from the second mating qualified giving about 35 per cent 

 of all daughters qualifying. The fourth generation of inbred daughters from 

 one brother x sister mating and two half-brother x sister matings all exceeded 

 10 per cent in range mortality. No inbred daughters were retained in the last 

 generation. It is evident that range mortality did increase under inbreeding. 



Check daughters showed a variable percentage qualifying for low range mort- 

 ality. The minimum figure was about 53 per cent and this occurred in 1931 

 Two later generations of check daughters showed 61 and 62 percent qualifying. 



Crossing inbred lines in 1932 gave only daughters with low range mortality , 

 while in 1933 mortality in such daughters rose to a very high figure. 



The age at sexual maturity of the inbred daughters did not change significantly 

 in four generations. Crossing inbred lines in two generations greatly increased 

 the percentage of early maturing daughters as compared with the inbreds. The 

 check daughters showed a higher percentage of early maturing birds than the 

 inbreds in every generation. These data indicate in a rather limited way that 

 inbreeding does immediately retard sexual maturity but that continued inbreed- 

 ing does not increase this effect. 



Inbreeding had little effect on the weight at first egg. The last generation of 

 inbreds shewed only 25 per cent qualifying for the weight standard, but the 

 number of daughters concerned is entirely too small to be conclusive. The 

 first cross of inbred lines gave a high percentage of daughters of satisfactory 

 weight, but this result did not appear in the second generation produced by 

 crossing inbred lines. Uniformly heavy weight was observed in the check 

 daughters. It is evident, therefore, from these data that inbreeding did not 

 greatly influence body weight at sexual maturity. 



The percentage of daughters lacking winter pause did not change perceptibly 

 under continued inbreeding. The first cross of inbred lines gave some improve- 



