Selection in Chickens for Retrogression of Tumors Caused by Rous Sarcoma Virus

SEVERAL investigators have conducted selection studies for resistance and susceptibility of chickens to avian leukosis. Hutt et al. (1941, 1945), Taylor et al. (1943), Waters (1945), McClary et al. (1951) and Bearse et al. (1963) all reported varying degrees of success in selecting divergent lines, from the same original stock, for resistance and susceptibility to avian leukosis complex. The duration of these selection experiments ranged from four to twenty-eight generations. The basis of selection most often used was full-sib family selection, while progeny testing was employed in some studies. The criterion of selection was the percentage mortality from all forms of leukosis during the rearing and laying periods. Natural exposure was usually the sole means of challenge. In a few instances, tumor material was placed in the drinking water. Cole (1968) demonstrated rapid progress in selecting two divergent lines for resistance and susceptibility to Marek’s disease. The birds were challenged…