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 t raits. Eight half-sib families were genotyped for 11 microsatellites and ma rker-QTL effects analysed using yield deviations (YD) as quantitative measu rements for the following traits: milk yield, protein yield, and protein pe rcentage. QTL analysis was performed by interval mapping based on multimark er 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 r esults, the first ones reported for QTL affecting milk traits in sheep, are discussed in relation to data available for cattle, a closely related spec ies.