Conditions Associated with Marine Lipid-Induced Milk Fat Depression in Sheep Cause Shifts in the In Vitro Ruminal Metabolism of 1-¹³C Oleic Acid

• Main Authors: Pablo G. Toral, Gonzalo Hervás, Vanessa Peiró, Pilar Frutos
• Format: Article
• Language: English
• Published: MDPI AG 2018-11-01
• Series: Animals
• Subjects: ewe; lipid metabolism; oxygenated fatty acid; rumen; stable isotope; <i>trans</i> fatty acid
• Online Access: https://www.mdpi.com/2076-2615/8/11/196

Shifts in ruminal oleic acid (OA) metabolism have received little research attention but recent studies have suggested their association with marine lipid-induced milk fat depression (MFD) in ewes and cows. Measurement of specific products of OA within the complex mixture of digesta lipids is however challenging. Therefore, this in vitro trial combined the isotopic labelling technique with the use of rumen inoculum from cannulated sheep fed a diet supplemented or not with 2% of fish oil (which has been demonstrated to cause MFD in dairy ruminants) to characterize the metabolism of OA in response to ruminal alterations associated with MFD. The products of ¹³C-OA after 24 h of incubation were analysed by gas chromatography-combustion isotope ratio mass spectrometry (GC-C-IRMS). Numerous ¹³C-labeled 18:1 intermediates and oxygenated FA were detected and no elongation or desaturation of ¹³OA occurred. Diet supplementation with fish oil (i.e., MFD conditions) resulted in no unique metabolites of ¹³OA but in relevant changes in the relative contribution of specific metabolic pathways. The inhibition of 18:0 saturation caused by this treatment appeared largely attributable to increased oxygenated FA proportion, in particular the candidate milk fat inhibitor 10-oxo-18:0, and warrants further research on the association between MFD and oxygenated FA. Changes in the concentration of ¹³C-labeled <i>trans</i> 18:1 intermediates but not in <i>cis</i> 18:1, were also observed.