In this work, the genetic variation of milk FA was investigated in three different bovine breeds, the Jersey, the Piedmontese and the Valdostana, and at different lactation stages. All animals were genotyped for 21 Single Nucleotide Polymorphisms located within nine candidate genes involved in lipid synthesis: diacylglycerol acyltransferase 1 and 2 (DGAT1, 2); stearoyl-CoA desaturase (SCD); growth hormone receptor (GHR); fatty acid synthase (FASN); acyl-CoA dehydrogenase (ACAD); fatty acid binding protein (FABP4); lipoprotein lipase (LPL); and leptin gene (LEP). The highest milk-fat Jersey breed also showed the highest content of saturated FA. Throughout lactation, the breeds showed a similar variation in the FA, with a decrease in the short-chain, this was accompanied by a general increase in the long chain FA at the end of lactation. The increase in long chain saturated FA was particularly evident in the case of the Jersey. The effect of SCD gene on the C14 desaturation index was confirmed; the DGAT1 gene was polymorphic only in the Jersey breed, but its effect was confirmed only on milk fat content; three further potential candidate genes were identified: first, the FABP4 gene, which was found to influence medium and long chain FA in all the breeds, but not the desaturation indices; second, the FASN gene, which was found to influence the amount of PUFA in the Piedmontese and the Valdostana, and third, the LPL gene, which was found to affect fat content in the Piedmontese.

The objective of this work was to characterize the complete coding region of the ovine acylCoA:diacylglycerol acyltransferase 1 (DGAT1) gene of three Italian sheep breeds: Sarda, Altamurana and Gentile di Puglia. Characterization was accomplished by direct sequencing of 8676 bp of the relevant DNA, including introns and partial 5' and 3' untranslated regions (UTRs). We detected five novel SNPs; one SNP (g.5553C>T) is located in intron 2, has similar frequencies in the three breeds and showed a negative association with milk fat content. More interesting is an SNP in the 5' UTR (g.127C>A), the occurrence of which is rare in the higher milk-fat breeds (Altamurana and Gentile di Puglia); it is located in the core sequence of Sp1, a putative binding site of transcription factors. This SNP showed a significant negative association with milk fat content in the Sarda sheep. Because DGAT1 plays a fundamental role in triacylglycerol synthesis, the novel detected SNP in the 5' UTR of the DGAT1 gene might explain, at least partially, the variation of fat content in the milk of Sarda sheep.

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BackgroundIdentification of genomic regions that have been targets of selection for phenotypic traits is one of the most challenging areas of research in animal genetics, particularly in livestock where few annotated genes are available. In this study a genome-wide scan using the Illumina SNP50K Beadchip was performed in the attempt to identify genomic regions associated with milk productivity in sheep. The ovine genomic regions encoding putative candidate genes were compared with the corresponding areas in Bos taurus, as the taurine genome is better annotated.ResultsA total of 100 dairy sheep were genotyped on the Illumina OvineSNP50K Beadchip. The Fisher’s exact test of significance of differences of allele frequency between each pair of the two tails of the distribution of top/worse milk yielders was performed for each marker. The genomic regions where highly divergent milk yielders showed different allele frequencies at consecutive markers was extracted from the OAR v3.1 Ovine (Texel) Genome Assembly, and was compared to the corresponding areas in Bos taurus, allowing the detection of two genes, the Palmdelphin and the Ring finger protein 145. These genes encoded non-synonymous mutations correlated with the marker alleles.ConclusionThe innovation of this study was to show that the DNA genotyping with the Illumina SNP50K Beadchip allowed to detect genes, and mutations in the genes, which have not yet been annotated in the livestock under investigation.

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