AbstractThe relationships between 12 polymorphic systems and bull fertility were studied in the Swedish Red and White dairy cattle population. The material consisted of 1447 young bulls with non-return rates based on at least 500 inseminations each. A reduced animal model including a full additive relationship matrix was used. Multiple regressions were fitted for the estimation of the average gene substitution effects as well as the gene-frequency-independent effects of additive gene action and dominance. To evaluate the results a multivariate analysis of variance, classical segregation analyses and marker frequency studies were performed. Significant associations were found between the F, B, Tf, S and C systems, and nonreturn rates, but the contribution of the markers to the total variation of non-return rates was small.