Many quantitative trait loci for feather growth in an F(2) broiler × layer cross collocate with body weight loci.

1. A genome-wide scan of 467 F(2) progeny of a broiler x layer cross was conducted to identify quantitative trait loci (QTL) affecting the rate of growth of the tail, wing and back feathers, and the width of the breast feather tract, at three weeks of age. 2. Correlations between the traits ranged from 0·36 to 0·61. Males had longer tail and wing feathers and shorter back feathers than females. Breast feather tract width was greater in females than males. 3. QTL effects were generally additive and accounted for 11 to 45% of sex average feather lengths of the breeds, and 100% of the breast feather tract width. Positive and negative alleles were inherited from both lines, whereas the layer allele was larger than the broiler allele after adjusting for body weight. 4. A total of 4 genome-significant and 4 suggestive QTL were detected. At three or 6 weeks of age, 5 of the QTL were located in similar regions as QTL for body weight. 5. Analysis of a model with body weight at three weeks as a covariate identified 5 genome significant and 6 suggestive QTL, of which only two were coincident with body weight QTL. One QTL for feather length at 148 cM on GGA1 was identified at a similar location in the unadjusted analysis. 6. The results suggest that the rate of feather growth is largely controlled by body weight QTL, and that QTL specific for feather growth also exist.

Mapping of quantitative trait loci for body weight at three, six, and nine weeks of age in a broiler layer cross.

An F2 chicken population was established from a cross of a broiler sire-line and an egg laying (White Leghorn) line. There were two males and two females from both lines in the base population. The F1 progeny consisted of 8 males and 32 females. Over 500 F2 offspring from five hatches were reared to slaughter at a live weight of 2 kg at 9 wk of age. Body weights at 3, 6, and 9 wk were recorded. The DNA was extracted from blood samples, and genotypes for 101 microsatellite markers were determined. Data of 466 individuals from 30 families were available for analysis. Interval mapping QTL analyses were carried out. The QTL significant at the genome wide level that affected body weight at two ages were identified on chromosomes 1, 2, 4, 7, and 8 and a QTL on Chromosome 13 influenced body weight at all three ages. Genetic effects were generally additive, and the broiler allele increased body weight in all cases. The effects for significant individual QTL accounted for between 0.2 and 1.0 phenotypic standard deviations and the sum of the additive effects accounted for approximately 0.75 of the line difference in body weight at 6 wk of age. The largest single additive effect was on chromosome 4, and the effect of substituting one copy of the gene was an increase in weight of 249 g. Interactions of the QTL with sex or family were unimportant. There was no evidence for imprinting or of two or more QTL at the same location for any of the traits.