4 MASS. EXPERIMENT STATION BULLETIN 344 



The behavior of egg weight after the first year is of considerable importance 

 to the breeder as well as economically. Hadley and Caldwell (1920) reported 

 maximum egg weight during the second laying year with a gradual decline in 

 later years. Atwood (1926) noted that White Leghorns almost attained maxi- 

 mum egg size in the second laying year. Hays (1929) showed that Rhode Is- 

 land Reds reached maximum egg weight in the second year. In general there 

 is not likely to be much change in egg weight after the second laying year. 

 On the average, the egg weight of the second year will range from 7 to 10 

 percent greater than during the first year. 



A considerable group of factors are known to affect egg weight. A number 

 of workers including Parkhurst (1933) have shown that deficient or inadequate 

 rations tend to reduce egg size. Parkhurst reported the following factors as 

 partly responsible for reduced egg size: Lack of vitamin D, grain and mash 

 as compared with an all-mash ration, lack of green food and oyster shell, and 

 the substitution of either soybean or meat meal for fish meal. Bennion and 

 Warren (1933) showed that temperatures above 85 degrees reduced egg size 

 from 15 to 20 percent. 



A number of inherited characters are known to affect egg weight. Among 

 the most important of these is body weight, according to the work of Atwood, 

 Jull, Robertson, Pearl, Funk and Kempster and others. Age at sexual maturity 

 also greatly affects egg weight according to Atwood, Jul], Funk and Kempster, 

 Hays, and others. Intensity significantly affects egg size according to studies 

 of Atwood, Funk and Kempster and Hays. Broodiness probably reduces egg 

 size according to Hays (1934). High persistency increased egg size in Hays' 

 (1934) studies. 



There are probably several Mendelian factors that directly control egg size. 

 Small egg size was found to be dominant by Benjamin (1920), Hurst (1921), 

 Kopec (1924), and Hays (1929). Waters and Weldin (1929), on the other hand, 

 suggested that large egg size may be dominant. 



Egg shape and shell texture have been very little studied from the genetic 

 standpoint. Both Benjamin (1920) and Kopec (1924) have stated that egg 

 shape is inherited, but no genetic analysis was reported. Shell texture has 

 been studied largely from the nutrition standpoint and in its relation to hatch- 

 ability. There are no reports concerning the behavior of shell texture in 

 inheritance. 



The mode of inheritance of shell color has been studied by a number of 

 workers. Hurst (1905) and Benjamin (1920) obtained an intermediate color 

 in F x by crossing brown-shelled and white-shelled breeds of fowl. Punnett and 

 Bailey (1920) believe that there is a major gene for brown shell color and several 

 minor genes. Intermediate shades depend on the presence of one or more minor 

 genes and white color upon the absence of major and minor genes. Kopec 

 (1927) reported that shell color depends upon several factors, each of equal 

 importance. In general it is probable that egg-shell color depends on multiple 

 factors and that first-generation crosses between brown and white races would 

 be expected to give intermediate shell color. 



