Blood grouping was used to investigate 1000 parentage cases in Swedish cattle. The blood samples were tested for 39 antigenic factors belonging to 9 different systems. One of the two possible bulls could be excluded as the sire in about 80% of the complete parentage cases in the Swedish Friesians (SLB) as well as the Swedish Red and White breed (SRB). The additional use of the transferrin systems in 79 of these cases resulted in a considerably increased efficiency. The probability of making exclusions with the aid of the various blood grouping systems was estimated from gene frequency data and showed good agreement with the results actually obtained. In the SRB the combined use of tests for cellular antigens and transferrins is expected to give solutions in about 84% of the complete paternity cases with two possible sires.
The value of using genotypic classifications in the complex blood group systems in parentage tests is discussed. Finally, attention is given to the difficulty encountered in parentage cases involving twin-born animals with erythrocyte admixture.