Association between SREBP-1 gene expression in mammary gland and milk fat yield in Sarda breed sheep☆

The aim of this study was to examine the expression patterns of SREBP-1 gene in milk somatic cells and its association with milk fat yield during early lactation in Sarda breed sheep. A sample of 20 Sarda ewes, aged between 4 and 5 years, in their third to fourth lactation were chosen. From each ewe 28 days after lambing milk yield was measured, and a 160 ml milk sample for the RNA extraction and to test somatic cells count and lactose, fat and protein contents were collected. From the obtained RNA, total cDNA was synthesized and the quantitative PCR was performed. The fat, proteins and lactose content showed many differences among the animals, but these variations were no correlated with the milk yield. The SREBP-1 gene expression resulted higher in the high milk fat producing ewes. The correlation analysis showed that the SREBP-1 expression level is directly related to the amount of milk fat (g/die) (P < 0.001), while the total RNA obtained from each sample was found to be related to the somatic cells number (P < 0.001). Instead the expression of this gene showed no relations with the concentration of fat in milk. Our data highlight that in sheep SREBP-1 gene is expressed in the mammary gland during early lactation. Moreover, the positive relationship between SREBP-1 gene expression and the milk fat yield suggests that SREBP-1 gene is required for the lipid synthesis in the sheep mammary gland.