164 



MASS. EXPERIMENT STATION BULLETIN 242 



Table 5 — Relation of Genetic Early Maturity to Vigor 



The proportion of genetically early-maturing pullets is highest in 1925, 

 lowest in 1923 and equal in 1922, 1924 and 1926. The table indicates no rela- 

 tion between heritable early maturity by years and mortality rate. The total 

 mortality in the early-maturing pullets is 31.08 per cent and the total in late- 

 maturing group is 29.92 per cent. These data indicate that genetic early ma- 

 turity is unrelated to vigor. 



7. Weight at first Egg in Relation to Mortaliti) Rale in the Laying Houses. 



Body weight represents a gross composite of size and is a useful practical 

 measure of rate of food metabolism as well as of meat value. It is import- 

 ant and desirable to know if body weight may be employed as a crude mea- 

 sure of vigor because it is subject to wide variation even when taken for a 

 flock of fowls of uniform age. Hays and Sanborn (1926, loc. cit.) have al- 

 ready shown the standard deviation in weigiit for this flock of birds to be 

 ±.75 pound when weights were taken at first pullet egg. Hays, Sanborn and 

 James (1924) found the standard deviation in weight for this strain to be 

 ±..54 pound when weights were taken at 150 days. That body weight offers 

 a possibility for selection purposes is apparent, but can it be made use of in 

 selecting for vigor? 



No difference in mean weight at first egg is shown between tlie daugiiters 

 of hens and of pullets on any year studied, and the mean weight of daughters 

 from all pullet mothers is 5.46 pounds and from hen mothers, 5.43 pounds. 

 Therefore, age of mothers at breeding time does not affect the weight of 

 daughters when they come into sexual maturity. 



Table 6 gives the mean weight at first egg for the 1923 flock as 5.6 pounds 

 which is about .2 pounds above the mean for five years. This greater weight 

 in 1923 is probably due to the fact that the pullets averaged nine days older 

 at first egg than the mean for the five years given in table 4. Taking the 

 five-year period as a whole, there is no significant change in weight at first 



