INCUBATION 
ject to no greater death rate than adult chickens. By the liv- 
ability of eggs, we mean the product of these two factors, i. e.: 
the percentage of chicks at four weeks of age based upon the 
total number of eggs set. 
As before mentioned, the fertility of eggs bears fairly defi- 
nite relation to the hatchability, so likewise the hatchability 
bears a relation to the livability of chicks. When poor hatches 
occur because of weak germs, as because of faulty incubation, 
this same injury to the chick’s organism is carried over and 
causes a larger death among the hatched chicks. 
Moreover, the relation between the two is not the same with 
all classes of hatches, but as hatches get poorer the mortality 
among the chicks increases at an accelerating rate. The fol- 
lowing table gives a rough approximation of these ratios: 
Per cent. of Per cent. of chick Per cent. of egg 
Hatchability. Livability. Livability. 
100 100 100 
90 95 85 
80 88 70 
70 84 50 
60 72 43 
50 55 27 
40 40 16 
30 24 7 
20 10 2 
10 2 1 
These figures are based on incubator data. Eggs set under 
hens usually give a hatchability of 50 per cent. to 65 per cent., 
and livability of 70 per cent. to 80 per cent. The reason for 
the greater livability is that the real hatchability of the eggs 
is 70 per cent. to 75 per cent., and is reduced by mechanical 
breakage. The hatchability of eggs varies with the season. 
This variation is commonly ascribed to nature, it being stated 
that springtime is the natural breeding season, and therefore 
eggs are of greater fertility. 
While there may be a little foundation for this idea, the 
chief cause is to be found in the manner of artificial incuba- 
tion, as will be discussed in a later section of this chapter. 
The following table is given as the seasonable hatchability 
for northern states. This is based on May hatch of 50 per 
cent: 
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