154 MASS. EXPERIMENT STATION BULLETIN 242 



Experimental Results 



Mortality rate during the pullet laying year is employed as the measure of 

 vigor in these studies. An outbreak of pox and roup in the flocks hatched in 

 1924 and 1925 has increased the mortality in the laying houses beyond the true 

 figure if no epidemic appeared. During the years 1922, 1923 and 1926 there 

 were no infectious disease outbreaks. 



1. A(je of Mothers in Relation to Vigor of Doatghters. 



Mothers of the pullets housed are divided into two classes; namely, pullet 

 mothers and hen mothers. The latter group includes largely yearlings, a few 

 two-year-olds and a very small number of older hens. The table below gives 

 the detailed figures by hatching years, with calculations made by families: 



Considering first the mortality rate in all chicks for the first eight weeks of 

 life, the fact is noted that losses from pullet mothers were consistently great- 

 er than losses from hen mothers in the last three years reported. The aver- 

 age percentage loss from pullet mothers is 2.78±1.70 per cent less than from 

 hen mothers for the hatching year of 1923. This difference is not significant 

 and is probably due to chance alone. Records of losses to eight weeks are not 

 available on the 1922 flock. 



A wide range in mortality rate from pullet mothers is shown in the four- 

 year period considered. The smallest losses occurred in 1923, with only5.58 

 per cent. In the years that followed the morality rate rose, reaching a maxi- 

 mum of 22.66 per cent in 1925. Losses for the first eight weeks in chicks from 

 hen mothers were lowest in 1924, being 6.06 per cent. The greatest losses 

 occurred in 1925 and amounted to 11.81 per cent. Comparing pullet and hen 

 mothers, the data show that chicks from pullet mothers are more variable in 

 death rate than those from hen mothers. There is also evidence of a greater 

 percentage of poor breeders among the pullets when judged by mortality rate 

 in chicks. 



The grand average for the four years is interesting. The 128 pullet mothers 

 tested gave 2103 chicks, while the 205 hen mothers tested gave 3538 chicks. 

 The grand average mortality rate in chicks for eight weeks is 15.50±2.26 per 

 cent from pullet mothers and 8.88±.69 per cent from hen mothers. The dif- 

 ference amounts to 6.62±2.36. While this difference is relatively large it is 

 less than three times as great as its probable error and offers inconclusive 

 statistical evidence of superiority of hen mothers over pullets in breeding high 

 vigor chicks. 



In table 1, the relation of age of mothers to vigor of offspring measured by 

 mortality rate of daughters in the laying houses may be studied. The mor- 

 tality rate in the laying houses is greater in the daughters of pullet mothers 

 in three out of five years but only for 1922 is the difference significant. For 

 1922 the mortality rate from hen mothers is 13.20±2.89 below that of pullet 

 mothers and its magnitude is more than four times as great as its probable 

 error. In 1923 and 1926 the losses from hen mothers were slightly, though 

 not significantly greater than from pullet mothers. 



Average mortality rate in daughters from 172 pullet mothers in the five- 

 year period is 34.48±3.54 per cent. Average mortality rate in daughters from 

 248 hen mothers in the five-year period is 31.74±2.94 per cent. The difference 

 is 2.74rb4.60 and must be due to random sampling alone and not to inherent 

 causes. 



