Effect of body weight on uniformity, livability, and skeletal development and strength of broiler breeder females

An experiment was conducted with broiler breeder females (up to 30 wks of age) to study the effect of body weight (BW) at 5 wks on BW uniformity, livability, and skeletal development and strength. At 5 wks of age, 160 females were randomly selected within a flock of 1,988, and they were reared without grading. Among these 160 females, the 40 with the lowest BW (Light Non-Graded, LNG) and the 40 with the highest BW (Heavy Non-Graded, HNG) were studied. LNG females, compared to HNG, had a higher BW coefficient of variation (CV) from 10 to 25 wks (P ≤ 0.05). At 25 wks, mortality of the LNG females was higher (20.0% vs. 2.5%, P = 0.027); they had shorter tibias (P ≤ 0.05), and a tendency to lower-tibia breaking strength (P = 0.085) and elastic modulus (P = 0.072). At 5 wks, their alkaline phosphatase was lower (2781 UI vs. 3839 UI, P = 0.023), and taking together 5 and 10 wks their osteocalcin was also lower (976 ng vs. 1239 ng, P = 0.029). Results indicate that without grading in rearing, light females had lower BW uniformity, lower livability, shorter and less resistant tibias than heavy females.