Abstract
Dairy products are often considered challenging for health due to their saturated fatty acid content, yet they also provide beneficial nutrients, some unique to ruminants. The degree of fat saturation is influenced by cows’ diets; grazing pasture enhances unsaturated fatty acids in milk compared with conserved forages. These benefits can be partially mimicked by feeding oilseeds and here we consider the impact on milk composition in a 2 × 2 trial, feeding rapeseed to both conventional and organic cows, finding very differing lipid metabolism in the 4 experimental groups. For milk fat, benefits of organic rather than conventional management (+39% PUFA, +24% long chain omega-3 and +12% conjugated linoleic acid (CLA)) appear complementary to those from feeding rape (+43% MUFA, +10% PUFA, +40% CLA), combining to produce milk 16% lower SFA and higher in MUFA (43%), PUFA (55%) and CLA (59%). Organic and rape feeding provide less omega-3 PUFA than the conventional and control diets, yet contrary to expectations, together they almost doubled (+94%) the omega-3 concentration in milk, implying a 3.8 fold increase in net transfer from diet into milk. Organic and rape feeding also gave lower trace-elements and antioxidants in milk. Greater understanding of these phenomena might enhance the sustainability of dairying.
Highlights
There is a lot of interest in nutritional contribution of milk and dairy products to our diet, possibly due to diverging attitudes towards the relationship between their consumption and our health
A survey on the fatty acid profiles in UK retail milk[6] found more conjugated linoleic acid (CLA, +32%), n-3 (+60%) and total polyunsaturated fatty acids (PUFA) (+24%) in organic compared with conventional milk
The 2 Nafferton dairy herds, established in 2006, are independent under common supervision; one managed to organic standards[15], allowing a system comparison without the bias of differing stockmanship or environmental conditions. This experiment consisted of two separate but simultaneous trials, one in the conventional and one in the organic herd, both of a nested design with cows in each herd randomly allocated to treatment groups, blocked for lactation number, days in milk, milk yield, gross milk composition and somatic cell count (SCC) based on the last recording prior to selection
Summary
There is a lot of interest in nutritional contribution of milk and dairy products to our diet, possibly due to diverging attitudes towards the relationship between their consumption and our health On one hand they are high in saturated fatty acids (SFA) which might challenge health but they supply many unsaturated fatty acids and antioxidants, beneficial to our health[1] and are a valuable source of quality protein, calcium and iodine[2,3]. Www.nature.com/scientificreports more MUFA and PUFA (30% more n-3 and 42% more CLA) in summer compared with milk purchased in the winter, when cows are likely to be housed and fed conserved silage rather than grazing We can mitigate these system and seasonal differences in milk composition to some extent, by offering feeds high in MUFA or PUFA such as whole soya beans, sunflower, rape or linseed to mimic the grazing missing for housed cattle[11,12]. All procedures were acceptable to internal ethical review, in accordance with EU Directive 2010/63/EU for animal experiments and approved by the Animal Welfare and Ethical Review Body at Newcastle University
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