(Co)variance components were estimated for a multi-trait sire and maternal grandsire (MGS) threshold model where first and later parity calving ease effects were analysed as correlated traits using Holstein data from the USA. Scores were on a 1 to 5 scale from easy or unobserved to extreme difficulty. Five samples of approximately 250 000 calvings were selected. Estimation was by AIREML and Gibbs sampling. Correlations from Gibbs averaged 0.93 for sire and 0.80 for MGS between first and later parity. AIREML gave similar correlations. Variances for the later parity group were less than for first parity, particularly for MGS. Evaluations, particularly for MGS, can be improved by treating first and later parities as correlated traits.

G. R Wiggans, C. P van Tassell, J. B Cole, L. LM Thornton

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume , , 01.92, 2006
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