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Abstract

A total of 7,472 progeny from 4 lines of chickens, a Black Australorp, a New Hampshire and 2 Leghorn lines, their crosses and reciprocal crosses were assessed for their pre- and post-hatching body weights, pre- and post-hatching growth rates and their associated egg weights. The interrelationships of these traits as they influenced growth and 7-week body weight were evaluated. The effects of these relationships were jointly considered as they influenced the genetic variation and subsequent estimates of the heritability (h²) of these traits. The results of the investigation showed that an adverse environmental effect due to hatching was definitely established. It took 2 weeks of growth after hatching for the chicken body weights to attain the same level of association with 7-week body weight that was previously shown in the body weights of 18-day old embryos. Multiple regression analyses showed that 1-week body weight and any subsequent growth periods successfully accounted for variation in 7-week body weight. The h² estimates obtained for all weekly growth rates as well as the 1-3, 3-7, and 1-7 week growth rates strongly indicated a major source of additive genetic variance was available in poultry populations that heretofore has not been directly utilized in body weight selection programs.