Associated effects and utilization of major genes other than these reducing body size in the fowl

Abstract

Besides genes influencing body size, the associated effect and possible usefulness of other identified genes of the domestic fowl were investigated. Several sex-linked genes (plumage color, feathering) allow visual sexing of day-old chicks, which represented the first practical application of Mendelian factors in poultry production. The pea-comb gene lowers heat dissipation through naked head appendages, reduces feed consumption of layers and improves their feed conversion rate by 2 %. Several genes suppressing pigment in the plumage have similar effects, i.e. slight depression of body weight and improvement of feed efficiency for egg production, better plumage condition toward the end of the laying year. The sex-linked albino allele, besides allowing day-old sexing in appropriate crosses, was found superior to the S colored gene for egg production with controlled lighting intensity (low during rearing, high during production). The naked neck gene, which suppresses 30 to 40 % of the plumage, has positive effects on meat yield ; by increasing heat dissipation it causes a poor feed efficiency at low or moderate ambient temperatures (20&dquo;C or below) but above 25°C and mainly above 30°C it has a beneficial effect on growth rate, viability (especially during heat stress), egg weight and female reproductive performance. Its incorporation in crosses for production in hot climates could be justified. The Frizzle gene, which also is likely to increase the heat exchange of the bird, does not have such marked effects on production traits. A slow feathering sex-linked allele, used for sexing, has been found linked with a « viral gene » in the Leghorn breed, hence a higher risk of leukosis infection through the egg of dams having this gene. For the Major Histocompatility Complex (B-locus), particular genotypes are associated with resistance or susceptibility to Marek’s disease, against which vaccines are not 100 % successful. The question may be raised of the choice of specified alleles in this perspective. Finally a single gene is responsible for a fishy egg taint in some brown-egg type laying stocks when rapeseed meal is incorporated into feeds. Its eradication in these populations was suggested. The utilization of Mendelian factors in selection programmes may concern particular traits for which direct selection is difficult or costly, or environments which are difficult to realize for the breeder. When a new major gene is introduced, the optimal conditions for its use are to be looked for, as it may be necessary to correct for some of its effects.