CYTOGENETIC STUDY OF EARLY CHICKEN EMBRYOS - EFFECT OF NAKED NECK GENE AND HIGH AMBIENT-TEMPERATURE

High ambient temperature (>30 C) decreases fertility of breeder hens, but this effect has been shown to be greatly reduced in females carryi ng the naked neck gene (Na). Sixty-four females each of the three diff erent genotypes, Na/Na (homozygous naked neck), Na/na+ (heterozygous), and na+/na+ (normally feathered), were equally distributed in two cli mate control rooms with individual cages, at a constant temperature of either 22 C or 31 C. Five hundred and seventy-six embryos were examin ed after 16 to 18 h of incubation for karyological analyses. Abnormali ties consisted of diploid-haploid and diploid-triploid chimeras. The f requency of chimeric embryos was significantly affected by dam genotyp e. Naked neck females showed a much lower proportion of abnormal embry os than normally feathered females whatever the temperature. The highe st proportion of chimeras was observed for the na+/na+ dams maintained at 31 C. However, the effect of temperature was not generally signifi cant.