Fig. 3

a–d Pedigrees from four subsets of the larger pedigree (Additional file 2: Figure S1) demonstrating a founder effect of four stallions for the IMM phenotype. Circles = females, squares = males. Open circles = phenotype unknown. Colored circles = IMM-affected with red = G/G genotype, blue = G/A genotype, and gray = A/A phenotype. Two of these founder stallions were traced back to the stallion in family A within one to three generations. For family D, the dam line traced back to the stallion in family A within four generations (Additional file 2: Figure S1)