BREEDING FOR EGG PRODUCTION 9 



the mean production about 25 eggs, so that the group having all five desirable 

 characters averaged to lay 252 eggs a year. 



The rate of progress in establishing these characters in the flock during the last 

 five \ ears is rather definitely indicated by the percentage of birds in the different 

 groups. The classes showing three and four of the desirable characters make up 

 59.34 per cent of the entire population. The classes having two of the characters 

 and those hav-ing all of the characters are equally represented with about 16 

 per cent. Theoretically the flock is improved only to the extent of about one- 

 sixth of what may be anticipated, for there is no known reason why 100 per cent 

 of the birds cannot carry all five desirable characters. There are at present 

 65,496 geneticalh' different classes of birds in the flock with respect to the five 

 characters considered. This fact shows why progress is slow in establishing char- 

 acters in a small flock, and it is very evident that little progress can be made in 

 flocks consisting of fewer than 500 individuals. 



Early Sexual Maturity 



Unpublished data show that the regression of annual egg production on age at 

 first egg is not strictly linear and that the correlation ratio shows a value of .6056 ± 

 .0112. Hays and Sanborn (1927b) have shown, however, that the net correlation 

 between age at first egg and annual egg production is insignificant and that early- 

 maturing birds generally lay more eggs only because they tend to be more intense 

 la\ ers and are generally more persistent. 



Even though early sexual maturity' in itself is not essential to high annual 

 production, its association with other essential characters gives it a high value 

 as a selection unit in production breeding. This character was the first to be 

 selected for in this experiment, was reasonably well established first in the flock 

 hatched in 1917, and has behaved with a high degree of constancy up to the 

 present time. 



Early maturit\- behaves in inheritance as a dominant to late maturity as Hays 

 (1924) showed. Two independent dominant genes, 2 E and E', are concerned, 

 either of which will enable pullets to begin la\ing at 215 days or less. Gene E 

 is sex-linked and is transmitted by males to both sons and daughters and by 

 females to their sons alone. Gene E' is autosomal and is transmitted equally 

 b>- both parents. No cumulati\e eff^ect has been discovered for these genes. . 



High Intensity 



High winter intensity (large clutch size) is an inherited character that has a 

 very significant effect on annual egg production. Winter clutch size was shown 

 by Hays and Sanborn (1927a) to be significantly correlated with production, 

 giving a value of -|-. 3544 + .0117. The same workers (1932) showed that the 

 regression of annual production on winter clutch size is non-linear, giving a 

 correlation ratio of .4214. Ha}S and Sanborn (1927b) found the net correlation 

 between winter clutch size and annual egg production to be +-4944 + .0101 

 which shows clearly that high intensity is essential to maximum egg production. 



2In genetic terminology capital letters stand for dominant genes and small letters for recessive 

 genes. Individuals are said to be homozygous for a gene when they carry two doses as HH or hh 

 and heterozygous when they carry two different genes as Hh. The first class of individuals breeds 

 true for the character in question — they are prepotent. The second class gives two types of off- 

 spring, one carrying H and one carrying h, in equal proportions. The same general principles 

 apply to other genes discussed in this report. 



