Genetic analysis of the growth curve of Rous sarcoma virus-induced tumors in chickens

White Leghorn chicks homozygous for B 1 9 MHC haplotype were selected for 18 generations on tumor regression after inoculation in the wing web with an SR-D strain of Rous sarcoma virus (RSV) at 4 wk of age. Each chick wasassigned a tumor profile index (TPI) based on age at death and size of the tumor. During 18 generations, 2,010 birds were divergently selected on TPI for either progression or regression of the tumor (P and R lines). A Brody growth curve was fitted for each bird. Brody function parameters included the asymptotic tumor volume (A), the factor for increased growth in progression phase (K 1 ), the factor for decreased growth in regression phase (K 2 ), age at maximum volume (T m a x ), and maximum volume of the tumor (V m a x ). Tumor growth curves were found to be different according to line, sex, and restriction fragment pattern Y complex Rfp-Y MHC haplotype (Yw* 1 5 , Yw* 1 6 , and Yw* 1 7 ). Within the P line, birds from the Yw* 1 6 haplotype reached V m a x at an earlier age than Yw* 1 5 and Yw* 1 7 , but with a lower V m a x value. Within the R line, tumor growth curves of birds from Yw* 1 6 and Yw* 1 7 haplotypes were similar. Rank correlations between the different parameters and TPI were low (between -0.26 and 0.36). Heritability estimated by the sire component was high for V m a x (0.73). Heritabilities of T m a x and K 2 were moderate (0.20 to 0.23 for T m a x and 0.18 to 0.21 for K 2 ) allowing these traits to be used as selection criteria. Heritabilities of A and K 1 were lower than 0.12. Modeling the growth curve should contribute to better distinction between progressors and regressors.