Abstract
BackgroundMastitis is the most prevalent disease in dairy sheep with major economic, hygienic and welfare implications. The disease persists in all dairy sheep production systems despite the implementation of improved management practises. Selective breeding for enhanced mastitis resistance may provide the means to further control the disease. In the present study, we investigated the genetic architecture of four mastitis traits in dairy sheep. Individual animal records for clinical mastitis occurrence and three mastitis indicator traits (milk somatic cell count, total viable bacterial count in milk and the California mastitis test) were collected monthly throughout lactation for 609 ewes of the Greek Chios breed. All animals were genotyped with a custom-made 960-single nucleotide polymorphism (SNP) DNA array based on markers located in quantitative trait loci (QTL) regions for mastitis resistance previously detected in three other distinct dairy sheep populations.ResultsHeritable variation and strong positive genetic correlations were estimated for clinical mastitis occurrence and the three mastitis indicator traits. SNP markers significantly associated with these mastitis traits were confirmed on chromosomes 2, 3, 5, 16 and 19. We identified pathways, molecular interaction networks and functional gene clusters for mastitis resistance. Candidate genes within the detected regions were identified based upon analysis of an ovine transcriptional atlas and transcriptome data derived from milk somatic cells. Relevant candidate genes implicated in innate immunity included SOCS2, CTLA4, C6, C7, C9, PTGER4, DAB2, CARD6, OSMR, PLXNC1, IDH1, ICOS, FYB, and LYFR.ConclusionsThe results confirmed the presence of animal genetic variability in mastitis resistance and identified genomic regions associated with specific mastitis traits in the Chios sheep. The conserved genetic architecture of mastitis resistance between distinct dairy sheep breeds suggests that across-breed selection programmes would be feasible.
Highlights
Mastitis is the most prevalent disease in dairy sheep with major economic, hygienic and welfare implications
Principal component analysis French Lacaune, Spanish Churra, Italian Sarda and Greek Chios were among the sheep breeds analysed within the framework of the sheep HapMap project [20]
Principal component analysis (PCA) was performed to examine the relatedness among these dairy breeds using genotypes obtained with the Illumina OvineSNP50 Beadchip within the HapMap project
Summary
Mastitis is the most prevalent disease in dairy sheep with major economic, hygienic and welfare implications. All animals were genotyped with a custom-made 960-single nucleotide polymorphism (SNP) DNA array based on markers located in quantitative trait loci (QTL) regions for mastitis resistance previously detected in three other distinct dairy sheep populations. Mastitis is an inflammation of the mammary gland usually caused by pathogens, mainly bacteria, developed in the gland cistern after penetration through the teat canal. It is the most prevalent and costly disease in the dairy industry due to reduced and discarded milk, early involuntary culling, veterinary service and labour costs [1, 2]. Marker assisted selection or genomic selection based on genotyping of single nucleotide polymorphism (SNP) markers could enhance and expedite the efforts for genetic improvement
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