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

Abstract

Among the major genes reducing body size in the domestic fowl, the sex-linked dwarfing gene dw was the subject of numerous studies and of applications on an industrial scale.Its recessiveness ant the fact that it lowers the body weight of the bird by one third and its feed consumption by 20-25 % led to its utilization in female broiler parental lines, giving normal-sized broilers when crossed with a standard broiler male line. For egg production, the use in the industry is more difficult, due to the fact that in egg production stocks, especially those of smaller body size (leghorns), the introduction of this gene causes a lowering of egg number and mean egg weight. In spite of this, in medium-size brown egg type lines the dw gene improves feed efficiency, avoids feed restriction programs and reduces the frequency of cracked and of softshelled eggs. Hence research work has been done so as to better estimate the optimal conditions for the use of « mini-layers » : preferable incorporation of the gene into mediumsized laying stocks, avoidance of feed underconsumption, utilization in production conditions where feed savings are relatively most important. Another sex-linked mendelian factor from Bantam breeds, lowering body weight by only 10-15 % without any deleterious effect on egg numbers, could be useful in specific crosses.