In dairy cows, diet-induced milk fat depression (MFD) has been related to the downregulation of certain lipogenic genes in the mammary tissue. However, information in this regard is very scant in dairy ewes, and results are inconclusive. Therefore, this assay was conducted in sheep with the aim of studying the relationship between changes in the milk fatty acid (FA) composition and the mRNA abundance of genes involved in mammary lipogenesis, in response to a diet known to induce MFD. A total of 12 ewes were divided into two treatments (n=6) and received a TMR supplemented with 0 (control) or 17 (FO) g of fish-oil/kg DM, for 31 days. On days 0, 7 and 30 on treatments, milk samples were collected to analyze the FA profile by gas chromatography. On days -13, 8 and 31, samples of mammary secretory tissue were removed by biopsy and used for a candidate gene expression approach by quantitative reverse transcription-PCR. Data were subjected to ANOVA for repeated measures using a statistical model that included the fixed effects of diet, time, and their interaction, and the initial record measured at the beginning of the trial as covariate. The FO diet did not affect feed intake and milk yield (P>0.10) but, as expected, induced MFD and modified milk FA composition. Compared with the control, reductions in milk fat concentration and yield were not detected on day 7, but reached up to 25 and 22%, respectively, on day 30 (P<0.05). Increases in some putative antilipogenic FA (e.g., trans-10 18:1, trans-10 cis-12 18:2, and trans-9 cis-11 18:2; P<0.05) were accompanied by reductions in the mRNA abundance of genes such as ACACA, FASN, SCD1 and SREBF1 (P<0.05), which would support that the nutritional regulation of milk fat content and composition is mediated by transcriptional control mechanisms. Most changes in gene expression were identified on day 8 (i.e., on early stages on the treatments) and stayed relatively stable afterwards.

Trabajo presentado a la : 66th Annual Meeting of the European Federation of Animal Science (EAAP). Innovation in livestock production: from ideas to practice. (Varsovia (Polonia), 31 de agosto a 4 de septiembre de 2015).

Peer reviewed