α‐Linolenic Acid Transfer into Milk Fat and its Elongation by Cows

It was the purpose of this study ot explore to what extent α‐linolenic acids transferred into bovine milk fat if either fed as intact linseed or if infused as linseed oil (α‐linolenic acid content ≈︁ 55 wt%) into the abomasum. Two cows consumed 2000 g/d linseed for 9wk. Then two doses of linseed oil (500 or 250 g/d) were infused for 14 or 4 wk into the abomasum of the cows, respectively. There was no effect of linseed oil on milk production, milk fat and protein content, whereas linseed caused a slight decline of milk protein content simultaneously with a pronounced rise of trans fatty acids in milk fat. While during the linseed period only 1% of consumed α‐linolenic acid (C18:3n‐3) appeared in milk fat, on average 49 or 56% of infused C15:3 was transferred into milk fat depending on the infusion rate of linseed oil. There was only modest rise of about 0.25 wt% of desaturation/elongation metabolites (C20:5 plus C22:5) of α‐linolenic acid in milk fat indicating a low δ6‐desaturase activity of the cow. Docosahexaenoic acid (C22:6) was not found in milk fat. It is concluded that bovine lipid metabolism allows surprisingly high transfer rates of n‐3 fatty acids of linseed oil into milk fat and that there is the possibility to enrich milk fat with n‐3 fatty acids without affecting milk yield provided ruminal biohydrogenation is prevented.