Relationships among egg characteristics, chick measurements, and early growth traits in ten broiler breeder strains

This study evaluated egg traits, yolk utilization, chick conformation, and early growth rate in 10 broiler breeder strains. The strains included pure-, specialized- and commercial-line products. The 210 eggs/strain were weighed and randomly designated to 1 of 3 experimental determinations: 8 eggs for measurement of eggshell conductance, 52 eggs for determination of egg characteristics, and 150 eggs for incubation and chick traits. Egg characteristics included egg weight, specific gravity, yolk weight, albumen weight, albumen height, eggshell weight, and eggshell thickness. Chick traits included navel condition, hock color, chick length, shank length, and abdomen score by manual palpation. At hatch, half the birds per strain were dissected to assess the weight of the yolk sac, heart, liver, and breast muscle. The remaining chicks were randomly distributed into 4 rearing pens for a 14-d assessment of growth rate. There was a 3-g range in egg weight among the strains. Eggs from a pure line had the greatest amount of yolk (22.6 g), with yolk weight ranging to a low of 20.9 g in 2 other strains. The male line strain and 2 female line strains had the highest hatching weights (46.3, 46.5, and 45.4 g, respectively), whereas a commercial strain had the lowest hatching weight (43.1 g). Egg size affected chick weight more than did yolk size. The residual yolk mass at hatch ranged from 5.50 g (in the male line) to 3.70 g in the commercial strains. Residual yolk mass accounted for approximately 10 to 14% of chick BW at hatch. The abdominal palpation score correlated with actual hatch residual yolk weight (r = 0.50; P < 0.0001). At hatch, differences in breast muscle and internal organ weight were present. Shank length at hatch correlated more strongly with 14-d BW (r = 0.39; P < 0.0001) than did hatch weight and 14-d BW (r = 0.35; P < 0.0001). The results of this trial demonstrated significant strain variation in internal organ weight, residual yolk sac mass, and chick carcass reserves, which, when added together, resulted in observable differences in chick weights across strains.