Genetic evaluation of milking speed for Slovenian Holstein cattle regarding to different scoring approaches
The objective of this research was to determine differences between estimated variance components and heritability of milking speed for Slovenian Holstein cattle regarding to different scoring approaches. Milking speed was scored by two different scoring approaches. From year 1989 to 2004, milking speed was scored on scale of 1–3, while from year 2004, scale of 1–5 was applied in scoring of milking speed. For analysis, from both approaches, 71.757 records were available. For genetic evaluation of milking speed univariate model and multi-trait model was used. In univariate model milking speed data on scale of 1–3 was evaluated, while in multi-trait model, both, milking speed data on scale of 1–3 as one trait, and milking speed data on scale of 1–5 as second trait, was evaluated. Herd and residual variances were lower in multi-trait model in comparison with variances in univariate model, while genetic variance was higher in multi-trait model. Variances for all random effects in multi-trait model were higher for new trait (MS 5) than for old trait (MS 3). Heritability for MS 5 was considerably higher than heritability for MS 3 estimated from both models. Breeding values for MS 5 had almost three time greater standard deviation in relation to breeding values for MS 3 in multi-trait. Appliance of new scoring approach resulted in genetic variance increase, which finally resulted in higher heritability value, which would enable faster selection response. Further investigation based on revalorisation of economic value for milking speed in calculation of Total Merit Index is needed.