Quantitative trait loci affecting clinical mastitis and somatic cell countin dairy cattle

Norway has a field recording system for dairy cattle that includes recordin g of all veterinary treatments on an individual animal basis from 1978 onwa rds. Application of these data in a genome search for quantitative trait lo ci (QTL) verified genome-wise significant QTL affecting clinical mastitis o n Chromosome (Chr) 6. Additional putative QTL for clinical mastitis were lo calized to Chrs. 3, 4, 14, and 27. The comprehensive field recording system includes information on somatic cell count as well. This trait is often us ed in selection against mastitis when direct information on clinical mastit is is not available. The absence of common QTL positions for the two traits in our study indicates that the use of somatic cell count data in QTL stud ies aimed for reducing the incidence of mastitis should be carefully evalua ted.