Quantitative trait loci for resistance to trichostrongylid infection in Spanish Churra sheep

Abstract

BackgroundFor ruminants reared on grazing systems, gastrointestinal nematode (GIN) parasite infections represent the class of diseases with the greatest impact on animal health and productivity. Among the many possible strategies for controlling GIN infection, the enhancement of host resistance through the selection of resistant animals has been suggested by many authors. Because of the difficulty of routinely collecting phenotypic indicators of parasite resistance, information derived from molecular markers may be used to improve the efficiency of classical genetic breeding.MethodsA total of 181 microsatellite markers evenly distributed along the 26 sheep autosomes were used in a genome scan analysis performed in a commercial population of Spanish Churra sheep to detect chromosomal regions associated with parasite resistance. Following a daughter design, we analysed 322 ewes distributed in eight half-sib families. The phenotypes studied included two faecal egg counts (LFEC0 and LFEC1), anti-Teladorsagia circumcincta LIV IgA levels (IgA) and serum pepsinogen levels (Peps).ResultsThe regression analysis revealed one QTL at the 5% genome-wise significance level on chromosome 6 for LFEC1 within the marker interval BM4621-CSN3. This QTL was found to be segregating in three out of the eight families analysed. Four other QTL were identified at the 5% chromosome-wise level on chromosomes 1, 10 and 14. Three of these QTL influenced faecal egg count, and the other one had an effect on IgA levels.ConclusionThis study has successfully identified segregating QTL for parasite resistance traits in a commercial population. For some of the QTL detected, we have identified interesting coincidences with QTL previously reported in sheep, although most of those studies have been focused on young animals. Some of these coincidences might indicate that some common underlying loci affect parasite resistance traits in different sheep breeds. The identification of new QTL may suggest the existence of complex host-parasite relationships that have unique features depending on the host-parasite combination, perhaps due to the different mechanisms underlying resistance in adult sheep (hypersensitivity reactions) and lambs (immunity). The most significant QTL identified on chromosome 6 for LFEC1 may be the target for future fine-mapping research efforts.

Possibilities to breed for resistance to nematode parasite infections in small ruminants in tropical production systems

“…Quantitative trait loci (QTL) studies for nematode resistance, using microsatellite markers, have now been undertaken in many countries (Paterson et al, 1999;Beh et al, 2002;Diez-Tascon et al, 2002;Cockett et al, 2005;Davies et al, 2006;Moreno et al, 2006;Gutié rrez-Gil et al, 2009;Marshall et al, 2009). A conclusion from these published results is that most significant QTL effects tend to be scattered throughout the genome.…”

Confirmation of two quantitative trait loci regions for nematode resistance in commercial British terminal sire breeds

“…Although no causative mutation has been identified for the FEC OAR3 QTL, the effect is often presumed to be mediated through INFG in sheep (Stear et al, 2009). Two QTL studies have reported an OAR14 FEC QTL, one in Blackface sheep (Davies et al, 2006) and the other in lactating Spanish milk sheep (Gutierrez-Gil et al, 2009), but the QTL positions were different in these two studies and neither study suggested any possible candidate genes underlying the QTL. Recently, however, in a comparative genomics study of TLR signalling in five species, Jann et al (2009) assigned IRF3 using both in silico and radiation hybrid mapping to OAR14, within the region covered by our markers.…”

“…Furthermore, these regions contain plausible candidate genes, namely, interferon-g (IFNG) and possibly genes located in the major histocompatibility complex, respectively. The region on OAR14 has only been observed in Blackface sheep (Davies et al, 2006), although another OAR14 FEC QTL was reported in Spanish milk sheep (Gutierrez-Gil et al, 2009). The region described by Davies et al (2006) contains interferon regulatory factor (IRF3), a toll-like receptor (TLR)-related gene.…”

Detection of QTL Underlying Milk Traits in Sheep: An Update

“…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. The average family size in this daughter design was around 110, ranging from 47 to 223 daughters per sire.…”

“…Because of the low to moderate heritability estimated for indicator traits in adult dairy sheep and the difficulties of routine collection of phenotypic indicators detection of genetic markers associated with these traits could be use to improve the efficiency of classical breeding. In Churra Spanish sheep, the genome scan reported by Gutiérrez-Gil et al (2009b) describes a genome-wise significant QTL on OAR6 influencing faecal egg count. Four other chromosome-wise significant QTL were found for faecal egg count and anti-Teladorsagia circumcincta Larvae IV IgA levels.…”