BREEDING FOR EGG PRODUCTION 255 
of breed or strain (Fig. 128). Breeding and selection will make it 
possible to reduce the number of weak ones to a minimum. 
Lack of Vigor.—The following are some of the common causes 
of loss or lack of vigor as determined by Rice and Rogers:* 
1. Increased Productiveness.—In its wild life the ancestor of 
the domestic hen laid but few eggs a year, perhaps a dozen. The 
modern hen is expected by good care and management to lay 
from 120 to 160 a year, and, at the same time, these eggs, or some 
& eer” | 
Fie. 128.—Strong and weak males. Contrast the bright protruding eye, erect carriage, 
and short heavy spur in the one and the low tail, sunken eye, long slender spur, and drooping 
carriage in the other. 7 
of them, must be hatched into chicks with as much strength and 
vigor as the parent. It is evident that any increase in the produc- 
tion of eggs must be accomplished by a proportionate increase in 
the physical strength of the bird, to enable her to assimilate the 
increased amount of feed required for this increased production. 
2. In-and-in Breeding Without Regard to Vigor.—Inbreeding 
is often resorted to in order that the high producing qualities may 
be better and more quickly fixed; but, where due consideration is 
not at the same time given tovigor, loss of vitality is bound to follow. 
* Cornell Reading Course (‘‘Constitutional Vigor in Poultry Breeding’’). 
