Potential benefits from multitrait evaluation - an example in selection for mastitis resistance based on somatic cell score and udder conformation. A simulation study

Multitrait evaluation methods have potential benefits when used to select for mastitis resistance. Six alternatives were simulated where 1000 sires having 10 different grand sires had 50 (27) or 100 (55) daughters for somatic cell scores (figures for udder conformation), with a distribution expressed as standard deviation of 0 (0), 10 (5) and 20 (10) (figures for udder conformation). Indirect evaluation methods for not observed mastitis resistance using a multitrait method were always better than indirect evaluation methods based on genetic regression on somatic cell scores, fore udder attachment and udder depth. Evaluations were nearly as accurate as direct evaluation using single trait evaluation of mastitis resistance, especially for low numbers of daughters per sire. Correlations between true breeding values and estimates were between 0.55 and 0.71 for direct and 0.52 and 0.62 for indirect selection using the multitrait method. Combined evaluation, grouping direct information on mastitis resistance and indirect through somatic cell score and udder conformation, consistently gave higher correlations between true and estimated breeding values for mastitis resistance relative to evaluation from direct recording only, with values between 0.65 and 0.77.