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Abstract
1. The inheritance of, and genetic and phenotypic correlations between, plasma insulin‐like growth factor‐I (IGF‐I) and 28‐(28dW) and 56‐d (56dW) body weight, 28‐ to 56‐d body weight gain (BWG), food intake (FI), food conversion ratio (FCR) and abdominal fatness (AF) at 56 d were determined by sib analyses in a population of 327 pedigreed progeny produced by matings between 18 cockerels and 72 pullets from a broiler strain of chickens bred at random for 8 generations.
2. Plasma IGF‐I was measured in fed (IGF‐If) and fasted (IGF‐IS) birds at 42 d.
3. Heritability estimates (sire + dam) were: 28dW 0.35 ± 0.11, 56dW 0.49 ± 0.13, BWG 0.51 ± 0.13, FI 0.55 ± 0.13, FCR 0.73 ± 0.14, AF 0.49 ± 0.13, IGF‐If 0.10 ± 0.08, IGF‐IS 0.08 ± 0.08.
4. The low heritability estimates with their high standard errors for the IGF‐I measures precluded the calculation of meaningful genetic correlations between these and the performance traits. There were moderate to strong positive genetic correlations between 28dW, 56dW, FI and AF.
