Genet. Sel. Evol. 35 (2003) 219-238
DOI: 10.1051/gse:2003005

Estimation of genetic variability and selection response for clutch length in dwarf brown-egg layers carrying or not the naked neck gene

Chih-Feng Chen^{a, b} and Michèle Tixier-Boichard<sup>a

a</sup>  Laboratoire de génétique factorielle, Département de génétique animale, Institut national de la recherche agronomique, 78352 Jouy-en-Josas Cedex, France
^b  Department of Animal Science, National Chung-Hsing University, Taichung, Taiwan

(Received 13 May 2002; accepted 12 August 2002)

Abstract
In order to investigate the possibility of using the dwarf gene for egg production, two dwarf brown-egg laying lines were selected for 16 generations on average clutch length; one line (L1) was normally feathered and the other (L2) was homozygous for the naked neck gene NA. A control line from the same base population, dwarf and segregating for the NA gene, was maintained during the selection experiment under random mating. The average clutch length was normalized using a Box-Cox transformation. Genetic variability and selection response were estimated either with the mixed model methodology, or with the classical methods for calculating genetic gain, as the deviation from the control line, and the realized heritability, as the ratio of the selection response on cumulative selection differentials. Heritability of average clutch length was estimated to be , with a multiple trait animal model, whereas the estimates of the realized heritability were lower, being 0.28 and 0.22 in lines L1 and L2, respectively. REML estimates of heritability were found to decline with generations of selection, suggesting a departure from the infinitesimal model, either because a limited number of genes was involved, or their frequencies were changed. The yearly genetic gains in average clutch length, after normalization, were estimated to be and with the classical methods, and with animal model methodology, for lines L1 and L2 respectively, which represented about 30% of the genetic standard deviation on the transformed scale. Selection response appeared to be faster in line L2, homozygous for the NA gene, but the final cumulated selection response for clutch length was not different between the L1 and L2 lines at generation 16.

Key words: dwarf chicken / naked neck gene / clutch length / genetic variability / selection response

Correspondence and reprints: M. Tixier-Boichard
    e-mail: boichard@jouy.inra.fr

© INRA, EDP Sciences 2003