Mapping quantitative trait loci for milk production traits on ovine chromosome 6

Spanish Churra sheep were studied in a daughter design for the presence on chromosome 6 of quantitative trait loci (QTL) influencing milk production traits. Eight half-sib families were genotyped for 11 microsatellites and marker-QTL effects analysed using yield deviations (YD) as quantitative measurements for the following traits: milk yield, protein yield, and protein percentage. QTL analysis was performed by interval mapping based on multimarker regression principles. Significance thresholds were estimated through a permutation test followed by a correction for multiple testing. The results suggest a region on ovine chromosome 6, close to the casein cluster, with an influence on milk traits and particularly on protein percentage. These results, the first ones reported for QTL affecting milk traits in sheep, are discussed in relation to data available for cattle, a closely related species.