It is practically impossible to increase egg production beyond a certain point in any flock of chickens without proper regard to mating and breeding. The old adage that it is impossible to squeeze blood out of a turnip also holds true in poultry keeping for, no matter how much care is given the birds, they cannot lay eggs beyond their HEREDITARY capacity.
As with egg production, hatchability, egg size and body weight cannot be increased beyond certain limits unless some constructive breeding program is followed. Altho this bulletin will deal with linebreeding for higher egg production, the same principles will apply for increasing hatchability, egg size and body weight.
Knox, C. W.
"A simple linebreeding program for poultry breeders,"
Bulletin: Vol. 22
, Article 1.
Available at: https://lib.dr.iastate.edu/bulletin/vol22/iss258/1