Enriching milk fat with n−3 polyunsaturated fatty acids by supplementing grazing dairy cows with ruminally protected Echium oil

Echium oil is a naturally rich source of stearidonic acid (SDA; C18:4n−3), an n−3 polyunsaturated fatty acid (n−3 PUFA) which is a precursor to the long chain (LC) n−3 polyunsaturated fatty acids (LC n−3 PUFA) eicosapentaenoic (EPA, C20:5n−3) and docosahexaenoic (DHA, C22:6n−3). The latter are LC n−3 PUFA for which there is accumulating evidence for positive cardiovascular health claims in human consumers. To determine the extent to which SDA supplementation can enrich milk fat with EPA and DHA, we supplemented 5 dairy cows on irrigated pasture with Echium oil for 10 d. The oil supplement was ruminally protected against biohydrogenation by using a protein–aldehyde matrix. Milk samples were collected during supplementation and 1, 2 and 30 d after supplementation ceased. Echium oil supplementation had no effect on levels of milk crude protein, fat, lactose and solids-not-fat. Average daily milk yield gradually declined as the period of supplementation progressed, and returned to pre-supplementation period levels after withdrawal of the supplement. The proportions of α-linolenic acid (ALA, 18:3n−3), SDA, EPA and total n−3 PUFA in milk fat increased in response to supplementation. The initial (Day 1) and final (Day 10) concentrations (in mg/l) of ALA, SDA, EPA and DPA in whole milk were 463 ± 29.2 versus 877 ± 63.1, 38 ± 8.6 versus 144 ± 12.4, 13 ± 6.2 versus 76 ± 9.0 and 45 ± 4.5 versus 65 ± 4.3, respectively. ALA, SDA, EPA and total n−3 PUFA concentrations increased linearly with increasing days of supplementation, while increases in DPA concentrations were curvilinear with a 3–4 d delay in their rise. DHA was not detected in milk fat. In terms of fatty acid yield/cup (i.e., 250 ml) of whole milk, enrichment of milk with EPA amounted to an increase from around 3.1–13.9 mg. As there was no change in DHA content, the long-chain n−3 PUFA content based on EPA alone was less than half of the cut-off point for omega-3 “source” claim (30 mg EPA + DHA per human serving) for foods in Australia. However, the total n−3 PUFA content of milk increased from 559 ± 41.0 to 1162 ± 82.4 mg/l. Data suggest that this oil containing SDA enriched milk with EPA, but not DHA. Dose response and large scale studies are needed to determine the optimal dietary inclusion rate and the commercial feasibility of SDA-containing oils as a means of increasing n−3 fatty acids in dairy cow milk.