Tip of The Day - October 11, 2016

Photo by Tom Semadeni

Bee's work

1988 Heterogeneity of Variances

Peter Sullivan et al.

Data on yield traits from a minimum of 147,316 to a maximum of 292,236 dairy records, across four regions of Canada were used in the study. The statistical model included relationships with male ancestors, and proven sires were treated as fixed effects if their contemporaries did not have daughter records in the data. Otherwise the model was identical to that in national sire evaluation.

For milk and fat yields, estimates of genetic variance and heritability differed from region to region, ranging from 0.31 to 0.48 for milk yield, and 0.31 to 0.54 for fat yield. Substantial differences were observed in an individual sire's proof, depending upon the region in which it was evaluated. Accounting for regional heterogeneity of variances seemed to have little effect on these differences. Re-ranking of sires was also minor after accounting for heterogeneous variances.

Conformation records are also to be analyzed ranging from 68,224 to 165,747 records.

Photo by Tom Semadeni