156 MASS. EXPERIMENT STATION BULLETIN 242 



Dntii ])resented in table 1 would appear to indicate first, that mortality 

 rate in chicks from pullet mothers tends to be somewhat greater than in chicks 

 from hen mothers. The proibability exists that the nutrient supply in the 

 hen's egg may be somewhat greater than in the pullet's egg because of larger 

 size and less intense production. Second, that there is no consistent or sig- 

 nificant difference in the vigor of laying pullets hatched from hen mothers 

 over those hatched from pullet mothers. 



^. HafchabUity of Mothers hi Relation to Vi(jor of Daucjhters. 



Hfitchability is measured over a period of eight weeks from March 25 to 

 May 15 each year. The percentage of fertile eggs hatched is used as the 

 hatchability index in each individual pullet or hen. 



Egg weight is not a factor in hatchability according to Stewart and Atwood 

 (190.«), Dunn (1922), Halbersleben and Mussehl (1922), Jull (1925), Hays 

 ana Sumbardo (1927) and others; but the weight of chicks at hatching is in- 

 timately correlated with egg weight according to Halbersleben and Mussehl 

 (1922, loc. fit.), Jull (1925 loc. cit.) and others. 



Hatciuibilitj' furnishes a measure of embryonic vigor but there are no pub- 

 lished data on the relation of hatchability in families and mortality rate after 

 surviving daughters are placed in the laying houses. Stewart and Atwood 

 (J 909) do, however, present data on the mortality rate in chicks to three 

 Weeks of age from pullet mothers and from hen mothers. These workers give 

 mortality rate to three weeks on 840 chicks from hens and 591 chicks from 

 pullets of the White Leghorn breed. Mortality rates given are 5 per cent 

 and 14.5 per cent, respectively. Dunn (1922a) has shown that hatching power 

 and mortality rate in chicks to three weeks of age are independent. His data 

 were collected on White Leghorn pullets and hens. The mortality rate for 

 the first three weeks was about 13 per cent of all chicks. 



Tahle 2 shows that the mean percentage of fertile eggs hatched is slightly 

 greater from hen mothers than from pullet mothers on each of the five years 

 reported. The differences are not great hut are probably statistically sig- 

 nificant. The range of variability by years is also greater in the pullet group 

 with a standard deviation of ±3.98 compared with ±1.68 for the hens. 



The mean hatchability of the 248 hens is 76.43±.51 per cent. The mean 

 hatchaibility of the 172 pullets is 70.78±1.20 per cent. The difference in means 

 amounts to 5.65±1.3. This difference is four times as great as its probable 

 error, which means that hens give higher hatchability than pullets in the flock 

 studied. 



Mortality rates in the laying houses are the same as reported in table 1. 

 Pullet mothers show^ greater variability of losses in daughters in the laying 

 houses than do hen mothers. The years 1923 and 1925 mark the lowest mor- 

 tality rate in the laying houses and on these two years the average hatch- 

 ability was highest of the period reported. The year 1924 gave the lowest 

 mean hatchability and by far the greatest mortality in the laying houses. In 

 1926 many of the embryos of the first four hatches died about the tenth day 

 apparently because of lethal effects of a 2 per cent coal tar disinfectant in 

 which the eggs were dipped before being incubated. It may be possible that 

 the sur\ivors of this treatment were a superior lot which would reduce mor- 

 tality in the laying houses to some extent. Tn general, the data on the rela- 

 tion of hatchability to mortality in the laying houses offer slight evidence that 

 high hatchability is associated with superior vigor. 



