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Joint Analysis of Quantitative Trait Loci for Clinical Mastitis and Somatic Cell Score on Five Chromosomes in Three Nordic Dairy Cattle Breeds

M. S. Lund^*,1, G. Sahana^*, L. Andersson-Eklund, N. Hastings, A. Fernandez, N. Schulman, B. Thomsen^*, S. Viitala, J. L. Williams^,2, A. Sabry^*, H. Viinalass^# and J. Vilkki

^* Department of Genetics and Biotechnology, Faculty of Agricultural Sciences, University of Aarhus, Research Centre Foulum, 8830 Tjele, Denmark
Department of Animal Breeding and Genetics, Swedish University of Agricultural Sciences, S-750 07 Uppsala, Sweden
Roslin Institute, Roslin, Midlothian, EH25 9PS, United Kingdom
MTT, Agrifood Research Finland, Biotechnology and Food Research, FIN-31600 Jokioinen, Finland
^# Institute of Veterinary Medicine and Animal Sciences, EMU, Kreutzwaldi 64, Tartu 51014, Estonia

¹ Corresponding author: Mogens.Lund{at}agrsci.dk

Five chromosomes were selected for joint quantitative trait loci (QTL) analyses for clinical mastitis (CM) and somatic cell score (SCS) in 3 breeds: Finnish Ayrshire (FA), Swedish Red and White (SRB), and Danish Red (DR). In total, 19 grandsires and 672 sons in FA, 19 grandsires and 499 sons in SRB, and 8 grandsires and 258 sons in DR were used in the study. These individuals were genotyped with the 61 microsatellite markers used in any of the previous QTL scans on the selected chromosomes. Within-family QTL analyses based on linear regression models were carried out for CM and SCS to identify the segregating sires for each region. On the segregating families, joint single-trait and 2-trait analyses were performed using variance components models. The analyses confirmed that QTL affecting CM or SCS, or both, segregate on Bos taurus autosomes (BTA) 9, 11, 14, and 18, whereas a QTL on BTA29 could not be confirmed. Our results indicate that there may be at least 2 linked QTL on BTA9, one that primarily affects CM and a second that primarily affects SCS. On chromosomes BTA11, 14, and 18, the joint analyses were only significant for SCS.

Key Words: quantitative trait loci • mastitis • somatic cell score • dairy cattle