Originally published as Genetics Published Articles Ahead of Print on August 24, 2007.

Genetics, Vol. 177, 1117-1123, October 2007, Copyright © 2007
doi:10.1534/genetics.107.077784

The Number of Loci That Affect Milk Production Traits in Dairy Cattle

* Animal Genetics and Genomics Platform, Department of Primary Industries Victoria, Attwood, 3049, Victoria, Australia and {dagger} Land and Food Resources, University of Melbourne, Parkville, 3052, Victoria, Australia

1 Corresponding author: Department of Primary Industries Victoria, 475 Mickleham Rd., Attwood, 3049, Victoria, Australia.
E-mail: amanda.chamberlain{at}dpi.vic.gov.au

We have used the results of an experiment mapping quantitative trait loci (QTL) affecting milk yield and composition to estimate the total number of QTL affecting these traits. We did this by estimating the number of segregating QTL within a half-sib daughter design using logic similar to that used to estimate the "false discovery rate" (FDR). In a half-sib daughter design with six sire families we estimate that the average sire was heterozygous for ~5 QTL per trait. Also, in most cases only one sire was heterozygous for any one QTL; therefore at least 30 QTL were likely to be segregating for these milk production traits in this Holstein population.