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Open Access Methodology

Quantitative trait loci mapping in dairy cattle: review and meta-analysis

Mehar S Khatkar, Peter C Thomson*, Imke Tammen and Herman W Raadsma

Author Affiliations

Centre for Advanced Technologies in Animal Genetics and Reproduction (ReproGen), and Co-operative Research Centre for Innovative Dairy Products, Faculty of Veterinary Science, University of Sydney, PMB 3, Camden NSW 2570, Australia

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Genetics Selection Evolution 2004, 36:163-190  doi:10.1186/1297-9686-36-2-163

The electronic version of this article is the complete one and can be found online at:

Received:4 July 2003
Accepted:29 October 2003
Published:15 March 2004

© 2004 INRA, EDP Sciences


From an extensive review of public domain information on dairy cattle quantitative trait loci (QTL), we have prepared a draft online QTL map for dairy production traits. Most publications (45 out of 55 reviewed) reported QTL for the major milk production traits (milk, fat and protein yield, and fat and protein concentration (%)) and somatic cell score. Relatively few QTL studies have been reported for more complex traits such as mastitis, fertility and health. The collated QTL map shows some chromosomal regions with a high density of QTL, as well as a substantial number of QTL at single chromosomal locations. To extract the most information from these published records, a meta-analysis was conducted to obtain consensus on QTL location and allelic substitution effect of these QTL. This required modification and development of statistical methodologies. The meta-analysis indicated a number of consensus regions, the most striking being two distinct regions affecting milk yield on chromosome 6 at 49 cM and 87 cM explaining 4.2 and 3.6 percent of the genetic variance of milk yield, respectively. The first of these regions (near marker BM143) affects five separate milk production traits (protein yield, protein percent, fat yield, fat percent, as well as milk yield).

quantitative trait loci; dairy cattle; review; meta-analysis


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