174 MASS. EXPERIMENT STATION BULLETIN 242 



Another very significant fact is hrouglit to light in taljle 13, namely, that 

 the percentage of families of perfect livability in chicks is greater from hen 

 mothers than from piilllet mothers but the percentage of perfect livability of 

 daughters in the laying houses is greater from pullet mothers. It seems prob- 

 able, therefore, that chick mortality removes a greater proportion of low 

 vigor chicks from pullet mothers than from hen mothers. Chicks from liens 

 are probably equipped with a larger supply of food nutrients from the egg 

 than are chicks from pullet mothers and for this reason the weaker individu- 

 als may survive longer only to succmub later to the severe strain of heavy 

 egg laying. These data illustrate the metiiod of securing higher vigor by 

 constantly using stock from low mortality families for breeding purposes. 



Summary and Conclusion 



Mortality in ciiicks to eight weeks of age is not a reliable index of vigor 

 because it bears little relation to mortality rates in the same families after 

 surviving daughters are placed in the laying houses. 



Hen mothers give more vigorous chicks to eight weeks of age than do pullet 

 mothers, but there is not a significant difference in the vigor of pullets from 

 hen mothers over pullet mothers after the pullets are confined to the laying 

 quarters. 



Hens showed higher hatciiability than pullets, and high hatchability shows 

 something of a tendency to be associated with low mortality in the laying 

 houses. High hatchaliility may therefore be used as one criterion of superior 

 vigor in resulting offspring. 



Late hatching decreases vigor in chicks to some extent, but has no effect on 

 vigor of pullets in the laying houses. 



Age at first egg does not affect vigor of pullets. 



Genetic early maturity has no relation to vigor of pullets. 



Weight at first egg is not a measure of vigor. 



Winter pause shows no relation to vigor as measured by mortality rates for 

 pullets in the laying houses. 



Intensity of laying does not affect vigor in pullets. 



The occurrence of broodiness before July first of the pullet laying year 

 appears to indicate superior vigor in the strain of birds studied. Non-broody 

 birds exhibit a higher mortality rate in the laying houses than do broody birds. 



There is no evidence of a relation between persistency and vigor in the data 

 presented. 



Winter egg production in low vigor l>irds is more varialile than in tiiose of 

 high vigor, but there is no difference in the number of eggs laid to March 

 first by vigorous and non-vigorous pullets. Winter egg record is not an indi- 

 cation of vigor, and no evidence is available that would indicate that heavy 

 winter laying reduces vigor. 



Four of the important heritable characteristics necessary for high e^g pro- 

 duction are independent of vigor; therefore, fixing early maturity, high in- 

 tensity, non-pause and high persistency does not decrease vigor. Tiie data 

 presented, however, indicate that eliminating l)roodiness in Rhode Island Reds 

 may reduce vigor. 



