I . mproved Egg Size high heritability of egg weight gives rapid response to selective breeding

Breeding for egg size differs in several important respects from other problems of poultry breeders. In the improvement of egg number, livability, hatchability and many other economically important characters, the breeder always selects in one direction. His goal is to have the birds in his flock lay the largest possible number of eggs, live as long as possible, at least until he i s ready to dispose of them, and produce fertile eggs all of which would hatch when incubated. Egg size is a trait where the most profitable type is not the extreme one: eggs can be too small to be of great economic value, and they can be too large for maximum net returns to occur. The most desirable egg size is an intermediate one; the most profitable range of egg weights being 24 to 26 ounces to the dozen. Although substandard egg sizes are more frequent than overly large ones, especially in flocks of high egg production, there are instances where breeders have had to reverse the direction of selection. A breeder may have started with a flock characterized by too small eggs. After several generations of selection for larger size, he may have found that too many of his birds were laying jumbo-sized eggs. Under such circumstances the breeder would be forced to reverse his standards of selection for egg size. The fact that the optimum condition is the intermediate one is only one of the reasons why such reversals of selection goals can occur. Another reason that is no less important is that of all economic traits in poultry, egg weight probably responds to selection most rapidly-the trait of egg weight shows extremely high heritability.