Novel Candidate Genes for Somatic Cell Count in Frizarta Dairy Sheep

Antonios Kominakis,Aggeliki Saridaki,George Antonakos

doi:10.11648/j.ijgg.20190704.13

Antonios Kominakis, Aggeliki Saridaki + Show 1 more

Open Access

https://doi.org/10.11648/j.ijgg.20190704.13

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Abstract

Aim of the present study was to identify genomic regions and candidate genes impacting on somatic cell count in the Frizarta dairy sheep. A total number of 482 Frizarta ewes genotyped with the medium density SNP array with available records on milk somatic cell count were used. Associations between genomic markers and the trait under study were detected by application of a multi-locus mixed model treating markers as fixed additive effects. Positional candidate genes identified within 1Mb flanking distances from significant markers were in silico prioritized based on their functional similarity to a training gene list including 1,120 genes associated with the term ‘immunity’. Association analysis pinpointed 4 chromosome-wide significant SNPs dispersed on four autosomes (OAR2, OAR18, OAR19 and OAR22). A total number of 37 positional candidate genes were identified within the searched genomic distances while 13 candidate genes were highly prioritized. Seven highly prioritized genes (NFIB, GFRA1, PSIP1, ARHGAP5, HECTD1, EMX2, STRN3) along with genes FREM1 and GPR33 had evidenced involvement in immune-related processes. Current results extent previous findings by providing novel candidate genes for the somatic cell count phenotype in dairy sheep.

Highlights

Somatic cell count (SCC) in dairy sheep milk is important in many aspects, including health and production
Milk with elevated SCC is usually considered as an indication of intra-mammary infection (IMI) and selection for decreased SCC could lead to reduced susceptibility to mastitis [2]
The percentage of polymorphonuclear neutrophilic leukocytes (PMN) increases to 50% at a SCC of 0.20·106 cells/ml and up to 90% at a SCC over 3·106 cells/ml [3] playing a protective role in the mammary gland [4]

Summary

Introduction

Somatic cell count (SCC) in dairy sheep milk is important in many aspects, including health and production. Mastitis in dairy ewes is associated with increased SCC in milk [1]. Milk with elevated SCC is usually considered as an indication of intra-mammary infection (IMI) and selection for decreased SCC could lead to reduced susceptibility to mastitis [2]. In dairy ewes, SCC can reach highest counts (e.g. 4·106 cells/ml) without mastitis symptoms, with milk still of normal macroscopic appearance [3]. SCC levels between affected and non-affected udders seem to clearly differentiate, with sheep milk from udders free from IMI having an average of 0.185·106 cells/ml when contrasted to an average equal to 1.445·106 cells/ml of infected halves [3]. The percentage of PMN increases to 50% at a SCC of 0.20·106 cells/ml and up to 90% at a SCC over 3·106 cells/ml [3] playing a protective role in the mammary gland [4]

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