The Effect of Selection and Genetic Factors on Resistance to Disease in Fowls—A Review

SummaryNeed for maximum short term improvement of economical efficiency has determined selection principles in commercial programmes which rarely left room for selection of viability. Breeding efforts have been limited to diseases which could not be controlled otherwise (Pullorum disease, Coccidiosis, Marek's disease). Selection for resistance has been quite successful in these cases. Most impressively, differences in resistance to Marek's disease remained unchanged for long periods and under different environments. Generally, the breeding efforts ended when the problem could be resolved by vaccination or medication. More recently, the identification of major genetic factors in disease resistance has revived interest in this area. It was found that resistance to leukosis infection is controlled by single genes and that the B blood-group system represents the major histocompatibility complex of the fowl. The role of these factors for disease resistance is discussed in the light of practical considerations. Simultaneous genetic improvement of resistance to classes of diseases might be a possibiity. Future progress in this area will depend much on an effective multidisciplinary approach in research, involving not only genetics and veterinary medicine but also immunology, biochemistry, ethology and perhaps other disciplines.