Quantitative Trait Loci Affecting Milk Production Traits on BTA 14 in Iranian Holstein Dairy Cattle: A Confirmation

The aim of this study was to refine the position of previously detected quantitative trait loci (QTL) on bovine chromosome 14 affecting milk production traits, using both linkage analysis (LA) and combined disequilibrium and linkage analysis (LDLA) methods, in Iranian Holstein dairy cattle. Analysis data was LRT (likelihood ratio test) and computed using the DMU (estimate the (co)variance components based on the average information of restricted maximum likelihood) and the results were compared with chi-square test and finally, the most likely location of QTLs was identified (P<0.05). A daughter design with 232 daughters from 10 sire families were considered and 10 microsatellite markers with a map distance of 0 to 63 cM located between markers ILSTS039 and DIK4361 (ILSTS011, DIK2598, DIK4884, DIK5080, CBDIKM002, ILSTS039, BM1508, CSSM066, CBDIKM004, and DIK4361) were genotyped. For milk and fat yield traits, the two mapping methods revealed a highly significant QTL was located within 20 to 60 and 54 to 60 cM interval (using LA) and within 12 to 60 and 60 cM interval (using LDLA), respectively. For fat percentage, a highly significant QTL was detected within 3, 12, 20, 36, 44 and 50 cM (using LA), but for LDLA, no significant location was detected. These results confirmed the findings of suggestive QTLs affecting milk production traits in the previous studies. Besides, the identified QTL in this study could be considered for marker-assisted evaluation and also for the selection of a refined set of candidate genes affecting the economic traits in Iranian dairy cattle breeding schemes.