Genes encoding equine β-lactoglobulin (LGB1 and LGB2): Polymorphism, expression, and impact on milk composition.

Lukasz Wodas,Alicja Borowska,Kamila Puppel,Beata Kuczynska,Mariusz Mackowski,Jakub Cieslak,Cristina Óvilo

doi:10.1371/journal.pone.0232066

Lukasz Wodas, Alicja Borowska + Show 5 more

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https://doi.org/10.1371/journal.pone.0232066

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Abstract

β-lactoglobulin is one of the most abundant milk whey proteins in many mammal species, including the domestic horse. The aim of this study was to screen for polymorphism in the equine LGB1 and LGB2 gene sequences (all exons, introns, and 5’-flanking region) and to assess potential relationship of particular genotypes with gene expression levels (measured in milk somatic cells) and milk composition traits (protein, fat, lactose, and total β-lactoglobulin content). Direct DNA sequencing analysis was performed for twelve horse breeds: Polish Primitive Horse (PPH), Polish Coldblood Horse (PCH), Polish Warmblood Horse (PWH), Silesian, Hucul, Fjording, Haflinger, Shetland Pony, Welsh Pony, Arabian, Thoroughbred, and Percheron—and revealed the presence of 83 polymorphic sites (47 and 36 for LGB1 and LGB2 genes, respectively), including eight that were previously unknown. Association analysis of the selected polymorphisms, gene expression, and milk composition traits (conducted for the PPH, PCH, and PWH breeds) showed several statistically significant relationships; for example, the two linked LGB1 SNPs (rs1143515669 and rs1144647991) were associated with total milk protein content (p < 0.01). Our study also confirmed that horse breed had significant impact on both gene transcript levels (p < 0.01) and on milk LGB content (p < 0.05), whereas an influence of lactation period was seen only for gene relative mRNA abundances (p < 0.01).

Highlights

Ruminants, including cattle, sheep, and goats, are the major source of the milk produced and consumed all over the world
Among them 81 were SNPs and 2 were InDels). Some of these were broadly distributed across the breeds, while some variants were detected in just one horse breed
Despite the great similarity between the composition of mare’s milk and human breast milk, there are several notable differences. One of these is the presence of β-lactoglobulin, which is a very abundant protein in equine milk, yet is totally absent in human breast milk [4]

Summary

Introduction

Ruminants, including cattle, sheep, and goats, are the major source of the milk produced and consumed all over the world. With the promotion of functional foods, there has been increased interest in milk from so-called minor dairy species. Special attention has been paid to mare’s milk, mainly on account of the similarity of its composition to human breast milk, its numerous health-promoting properties, and its low allergenicity. It is estimated that around 30 million people consume mare milk regularly, predominantly in Asia, where the tradition of kumis production continues to this day (such as Mongolia and Kazakhstan), and in some European countries (such as Germany and France) [1].

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