ESTIMATION OF GENOTYPE EFFECTS FOR MILK-PROTEINS WITH ANIMAL AND SIRETRANSMITTING ABILITY MODELS

The objective of this work was to estimate the contribution of milk pr otein genotype to production traits of Holstein cattle. Two approaches were employed. The first was based on an animal model analysis of mil k records in which cows were genotyped for milk protein variants. The second approach was the analysis of PTA of sires in which the sires we re genotyped for their milk protein variants. Results of the animal mo del analysis agreed qualitatively with previously published analyses o f cow records, indicating only a minor contribution of milk protein ge notype to production traits. Qualitative similarity was also found bet ween the analysis of sire transmitting abilities and the animal model. Algebraic results suggested, however, that an indirect analysis of pu blished sire transmitting abilities does not provide unbiased estimate s of differences in milk protein genotypes. Although analysis of PTA i s simple, only a direct analysis of genotyped cows with an animal mode l provides unbiased estimates of genotype differences.