8 MASS. EXPERIMENT STATION BULLETIN 384 



Body Weight at Sexual Maturity in Pullets 



Body weight at sexual maturity is of considerable importance because sexual 

 maturity marks the onset of the reproductive function. The mean weights of 

 pullets in the different emergent groups are recorded in table 6. The pullets in 

 the last five emergent groups were heavier than those of the two earliest groups, 

 but there was no significant difference in body weight among the last five groups. 



Table 6. — Relation of Length of Incubation Period to Body 

 Weight and Age of Pullets at Sexual Maturity 



Age at Sexual Maturity in Pullets 



The stock used does not vary widely in age at sexual maturity because it 

 closely approaches genetic purity for this character. Variations in age at first 

 egg, when they occur, must therefore be attributed largely to environmental 

 modifiers. For testing possible effects of length of the incubation period on mean 

 age at first egg, the data are summarized in table 6. 



It will be noted that the emergent groups were closely parallel in age at first 



egg and in mean weight at first egg; that is, the pullets from the two very early 



, emerging groups averaged about ten days younger than those from the five 



later groups. These data indicate that age at sexual maturity is afTectly slightly 



by the length of the incubation period. 



Winter and Annual Egg Production 



Winter egg production includes the number of eggs laid from first pullet egg 

 up to March 1. In order to discover whether there is any relation between the 

 length of the incubation period and subsequent winter egg production, the data 

 are summarized in table 7. 



There was a consistent decline in mean winter egg production as the length 

 of the incubation period increased. There was a decline in mean winter egg 

 production of about 30 eggs between the earliest emerging group and the sixth 

 emergent group. These rather limited data indicate that the length of the in- 

 cubation period bears an important relationship to subsequent winter egg pro- 

 duction. 



Annual egg production represents the number of eggs laid from first pullet egg 

 for a period of 365 days. Available data are assembled in table 7 to discover 

 possible relations between length of incubation period and annual egg production. 



