BREEDING FOR EGG PRODUCTION tl 



correlation between days broody and egg production in the pullet \ear is — .5630 

 ±.0097 in the station flock. 



Broodiness is inherited on a two-factor basis according to Goodale, Sanborn 

 and White (1920). Two dominant complementary genes, A and C, are necessary 

 to produce broodiness. There is no evidence of sex linkage, and non-broody 

 birds are of three general classes: (1) those lacking both A and C; (2) those 

 carrying A and lacking C; (3) those carrying C and lacking A. Classes 2 and 3 

 are very troublesome to the breeder because such females, though not exhibiting 

 broodiness, will produce broody offspring if mated with males carrying the gene 

 that they lack. This is one of the chief reasons why broodiness has never been 

 completeh" eliminated from any flock. Another obstacle in eliminating broodi- 

 ness lies in the problem of deferred broodiness. In such cases the instinct may 

 not appear in many females during the first or second laying years. This fact 

 renders an accurate progeny test of males almost impossible with the American 

 breeds. 



A constructi\e breeding program calls for the constant use of non-broody 

 hens for breeding and the use of progeny-tested males to the greatest extent 

 possible. 



Persistency 



Persistency- at the close of the pullet laying year has been shown by Hays and 

 Sanborn (1927b) to be the most important inherited character affecting annual 

 egg production. The net correlation between length of la\ing year and annual 

 production is -(-.7501 +.0063. This fact indicates that more than 56 per cent 

 of the variation in annual egg records is due to differences in persistency. Hays 

 and Sanborn (1933) have pointed out further that persistency higher than 365 

 days is desirable in breeders from the standpoint both of increasing egg production 

 and of reducing mortality in daughters. 



Hays (1927) has presented some evidence concerning the mode of inheritance 

 of high persistency. His data indicate that high persistency depends upon one 

 dominant autosomal gene, P. According to this report the dividing point 

 between birds genetically high and low in persistency lies at about 315 days from 

 the first pullet egg. In breeding for persistency, no females laying for a shorter 

 period than 315 days should be used for mating, and male breeders should carry 

 an equally good or superior inheritance for persistency. 



The Hatchability Problem 



Extensive experimental observations by many investigators indicate a wide 

 range in percentage of fertile eggs hatched b\' different birds. Experience also 

 furnishes evidence that constant selection for high hatchabilit\' is necessar\' in 

 improved flocks in order that hatchability may not decline. Experimental 

 workers are agreed that hatchability is an individual trait depending upon both 

 inheritance and environment. 



Egg size does not affect hatchability as Jull (1932) shows from his own studies 

 as well as from the work of other investigators. The physical characters of eggs 

 such as shape and shell texture do not influence hatchability if the eggs are nor- 

 mal. On the basis of these facts, the selection of hatching eggs for size and 

 physical characters does not seem to have any significant effect on hatchability. 



