Quantitative Trait Loci Affecting Milk Production Traits in Finnish Ayrshire Dairy Cattle

Abstract

A whole genome scan of Finnish Ayrshire was conducted to map quantitative trait loci (QTL) affecting milk production. The analysis included 12 half-sib families containing a total of 494 bulls in a granddaughter design. The families were genotyped with 150 markers to construct a 2764 cM (Haldane) male linkage map. In this study interval mapping with multiple-marker regression approach was extended to analyse multiple chromosomes simultaneously. The method uses identified QTL on other chromosomes as cofactors to increase mapping power. The existence of multiple QTL on the same linkage group was also analyzed by fitting a two-QTL model to the analysis. Empirical values for chromosome-wise significance thresholds were determined using a permutation test. Two genome-wise significant QTL were identified when chromosomes were analyzed individually, one affecting fat percentage on chromosome (BTA) 14 and another affecting fat yield on BTA12. The cofactor analysis revealed in total 31 genome-wise significant QTL. The result of two-QTL analysis suggests the existence of two QTL for fat percentage on BTA3. In general, most of the identified QTL confirm results from previous studies of Holstein-Friesian cattle. A new QTL for all yield components was identified on BTA12 in Finnish Ayrshire. (Key words: cofactor, dairy cattle, interval mapping, quantitative trait) Abbreviation key: BTA = Bos taurus chromosome, DYD = daughter yield deviations, FY = fat yield, F% = fat percentage, MY = milk yield, PIC = polymorphic information content, PY = protein yield, P% = protein percentage.

Quantitative trait loci for fertility traits in Finnish Ayrshire cattle

“…IV). On these chromosomes, fertility QTL were detected in the single trait regression analysis close to milk QTL [46] detected earlier and some of them had QTL regions affecting two different fertility traits. The analysed traits were DO, FT, CM, NRR, MY, PY, and FY.…”

“…When comparing the fertility QTL with the positions of the milk trait QTL detected in an earlier study in the same families [46], several milk and fertility QTL were found on the same chromosomes. For example, on BTA25, where QTL were detected for DO and FT at the end of the chromosome, QTL for milk yield and protein yield were also detected.…”

“…QTL analyses consisted of the following steps: (1) a genome scan was carried out using multiple linear regression for four fertility related traits; (2) the significant QTL detected from (1) and milk production QTL detected by Viitala et al [46] that overlapped with the fertility QTL were reanalysed with the variance component method using a single-trait model (STVC); (3) multitrait pleiotropic (MT P ) and linked (MT L ) QTL models were analysed when QTL for two fertility traits or one fertility trait and one milk yield trait [46] were detected on the same chromosome.…”

“…This was done because QTL for milk production were reported on these chromosomes by Viitala et al [46] in the same families. The STVC analyses detected QTL for MY on BTA1; for MY and PY on BTA5; MY, PY, and FY on BTA12; FY on BTA14 (Tab.…”

“…Multi-trait QTL analyses were carried out on eight chromosomes, which harbour QTL for more than one fertility trait or at least one fertility related trait and one milk production trait identified earlier by Viitala et al [46] in the same population. We selected the chromosomes based on the significance of the QTL in the regression analysis.…”