Quantitative trait loci underlying milk production traits in sheep

Abstract

Improvement of milk production traits in dairy sheep is required to increase the competitiveness of the industry and to maintain the production of high quality cheese in regions of Mediterranean countries with less favourable conditions. Additional improvement over classical selection could be reached if genes with significant effects on the relevant traits were specifically targeted by selection. However, so far, few studies have been undertaken to detect quantitative trait loci (QTL) in dairy sheep. In this study, we present a complete genome scan performed in a commercial population of Spanish Churra sheep to identify chromosomal regions associated with phenotypic variation observed in milk production traits. Eleven half-sib families, including a total of 1213 ewes, were analysed following a daughter design. Genome-wise multi-marker regression analysis revealed a genome-wise significant QTL for milk protein percentage on chromosome 3. Eight other regions, localized on chromosomes 1, 2, 20, 23 and 25, showed suggestive significant linkage associations with some of the analysed traits. To our knowledge, this study represents the first complete genome scan for milk production traits reported in dairy sheep. The experiment described here shows that analysis of commercial dairy sheep populations has the potential to increase our understanding of the genetic determinants of complex production-related traits.

Disentangling Prenatal and Postnatal Maternal Genetic Effects Reveals Persistent Prenatal Effects on Offspring Growth in Mice

“…Although this pleiotropic link between maternal and offspring traits must exist at some level (i.e., maternal effects must ultimately be caused by some feature of the mothers), we know very little about the connection from maternal loci to offspring trait variation through a set of known maternal traits. Maternal traits like milk quality characteristics, which may be largely responsible for maternal effects on offspring growth traits in livestock species (Meyer et al 1994), have been successfully mapped in various livestock species (e.g., Gutierrez-Gil et al 2009;Jiang et al 2010), making such loci candidates for maternal effects on offspring developmental traits. However, searches for candidate genes associated with obvious maternal traits, such as lactation, nursing, or nesting traits, in the intervals around the maternal-effect loci we identified did not yield any specific candidate genes, which is perhaps not surprising since these traits have few identified candidates in the genome (Blake et al 2011).…”

Detection of QTL Underlying Milk Traits in Sheep: An Update

“…This analysis method is the one followed for milk traits QTL mapping in the commercial sheep populations previously described. The analyses performed in Spanish Churra sheep were performed using HSQM (Coppieters et al, 1998) which implements the multimarker regression method described by Knott et al (1996) (Díez-Tascón et al, 2001;Gutiérrez-Gil et al, 2007, 2009a. In the Lacaune and Manech French populations, the QTL detection was carried out according to the methodology proposed by Knott et al (1996) and Elsen et al (1999) by within-sire linear regression .…”

“…Based on the same design a genome scan included in the framework of the European funded GeneSheepSafety project was planned to scan the 26 ovine autosomes. A total of 1421 ewes sired by 11 IA rams and distributed among 17 different flocks were used in this project for detection of QTL underlying classical milk traits (Gutiérrez-Gil et al, 2009a). Other traits of interest in dairy sheep production such as morphology traits (Gutiérrez-Gil et al, 2008; and resistance to mastitis and nematode gastrointestinal infections (Gutiérrez-Gil et al, 2007;2009b) were also recorded in the commercial population genotyped.…”

“…YDs are weighted averages of ewe's lactation yields minus solutions for management group, herd-sire, and permanent environmental effects (VanRaden & Wiggans, 1991). These are the quantitative measures that have been used in the QTL mapping experiments performed in Churra sheep (Díez-Tascón et al, 2001;Gutiérrez-Gil et al, 2007;2009a). Because rams do not have yield deviations, DYD, which are adjusted for mates´ merit, can provide a usefull, unregressed measure of daughter performance to use in grand-daughter designs (VanRaden & Wiggans, 1991).…”

“…From the initial studies on milk protein polymorphisms (Reviewed by Barillet et al, 2005), and the first description of a QTL in a dairy sheep breed (Diez-Tascón et al, 2001), some few reports of genome scans to identify QTL influencing milk production traits in this species can be found (Gutiérrez-Gil et al, 2009a;). The lower number of projects searching milk-related QTL in sheep when compared with the number of studies carried out in dairy cattle can be partially explained by the funding limitations that exist, for example, to establish a sheep experimental population as has been done in cattle in several occasions (Gutiérrez-Gil et al, 2009c;Eberlein et al, 2009).…”