Dairy ewes are less prone than cows to milk fat depression (MFD) but sufferthis syndrome when marine lipids are added to their diet to improve milkfatty acid (FA) composition. This is very detrimental as most ovine milk isused for cheese manufacture. However, there are large individualdifferences in MFD severity; the reasons behind this variability beinguncertain. This study was conducted in lactating sheep to test thehypothesis that differences in milk concentration of antilipogenic FA or inthe transcriptional regulation of mammary lipogenesis may account for thatindividual variation. We used 15 ewes receiving, for 35 d, a total mixedration supplemented with 0 (control; n = 5) or 20 g of fish-oil/kg DM [10animals were selected out of 22 and divided in those showing a strong(RESPON+, n = 5) or slight (RESPON-, n = 5) MFD]. Milk production andcomposition, and milk FA profile were recorded for 3 consecutive daysbefore and after treatments. Candidate gene expression was analyzed byquantitative reverse transcription-PCR on mRNA isolated from milk somaticcells collected before (d −2 or −1) and after (d 34 or 35) the dietarytreatments. Data were analyzed with the MIXED procedure of SAS 9.4 usingorthogonal contrasts. Milk production was not affected by the diets (P >0.10) but milk fat concentration decreased by 25.4% in RESPON+ and 7.6%in RESPON- (P < 0.001). Supplementation with fish oil enhanced (P < 0.01)the milk content of both potentially healthy FA (e.g., cis-9,trans-11 CLA,trans-11 18:1, or very long chain n-3 FA) and antilipogenic FA (e.g., cis-916:1, trans-10 and cis-11 18:1, trans-10,cis-15 18:2, trans-9,cis-11 andtrans-10,cis-12 CLA, and 10-oxo-18:0). Nevertheless, differences betweenRESPON- and RESPON+ were hardly detected. Consumption of the MFDinducingdiet was accompanied by reductions in the mRNA abundance ofACSS2, FASN, LPIN1 and INSIG1 (P < 0.10), but only SCD and GPAT4tended to differ between RESPON+ and RESPON- (P < 0.10). These resultsoblige to reject the hypothesis and conduct a thorough evaluation ofindividual responses at systemic, ruminal, and mammary levels to explainthe individual variation in MFD severity.

Resumen de la comunicación oral (invitada) presentada al: 2017 ADSA Annual Meeting #264. Pittsburgh, Pennsylvania (Estados Unidos), 25-28 de junio de 2017.

Peer reviewed