Selection for Body Weight at Eight Weeks of Age 2. Correlated Responses of Feathering, Body Weights, and Reproductive Characteristics

Heritability, Maternal Effects and Nicking in Relation to Sexual Maturity and Body Weight in White Leghorns

Using adult female chickens fed and managed in a similar manner, Jaap and Thompson (8) ^ demonstrated heritable differences in body shape. The criteria of conformation used were the ratios obtained by dividing length of shank, body depth, and length of keel by the cube root of body weight. Such measures of body conformation in live birds have proved valuable for predicting visual body shape (7) when chickens or turkeys are being prepared for human consumption. The observations reported in earlier papers (7, 8) were made in the latter part of the growth period and at maturity. The present study was planned to determine whether the above measurements may be used to detect heritable differences in body shape of live chickens at an early stage of growth, the so-called ''broiler'' ages. A large proportion of market poultry is killed early in the growth period. In order to reserve for breeders those chickens having superior body conformation, it is important to measure body shape and other characteristics of market quality as early as 8 weeks after the chicks are hatched. In chicks of equal table quality, those whose body weights increase most rapidly during the first 8 to 12 weeks of life are generally considered the most profitable. More food is required for maintenance in the slower growing birds and turn-over of investment is not so rapid when growth is slow. These are probably some of the reasons why periodic increase in body weight is used in so large a number of studies as the measure of economic efficiency in the growth of chickens. It is evident that the most rapidly growing chickens do not, by virtue of their growth rate, necessarily have a body form that is pleasing to the eye.

N. F. Waters

Papers

Body Weight, Egg Weight, Sexual Maturity and Growth Rate in the Domestic Fowl