Differences in composition between organic and conventional milk
by Gilian Butler, Jacob H. Nielsen, Tina Slots, Chris Seal, Michael D. Eyre, Roy Sanderson and Carlo Leifert
||Differences in the composition between organic and conventional milk in relation to fatty acid and fat soluble antioxidant concentrations were demonstrated in a study of 109 milk samples from 25 commercial farms. The farms represented three different production systems: conventional, high input farms; organically-certified low input farms; and non-organically certified low input farms
Versatile role of milk fatty acids
The fatty acid (FA) and fat-soluble antioxidant composition in milk fat is known to affect processing and sensory quality of dairy products, and may also affect their nutritional value.
The degree of saturation in milk fat also has a bearing on the hardness, texture and taste of manufactured dairy products, particularly butter and cheese. The presence of longer chain saturated fatty acids (SFA) increases the hardness of butter, whilst milk with a high proportion of unsaturated FA content tends to give softer products (e.g., more spreadable butter).
High dietary intakes of saturated fatty acids (which account for 60 to 70% of milk fat) are a risk factor for development of e.g., obesity, cardiovascular diseases (CVD), and impaired insulin sensitivity. In contrast, dietary intake of certain unsaturated fatty acids, in particular conjugated linoleic acid (CLA), vaccenic acid (VA) and omega-3 fatty acids (n-3 FA) and fat soluble antioxidants (e.g. α-tocopherol, carotenoids) has been linked to potential health benefits.
Effect of production systems on fatty acid content
Milk and dairy products from certified organic dairy production systems have been reported to contain higher concentrations of polyunsaturated fatty acids, αLA (the main n-3 FA in milk), and/or CLA, and fat soluble antioxidants than those from high input conventional production. These studies did not include non-organic, low-input systems in comparisons.
Milk composition is known to change when switching from outdoor grazing to indoor forage-based diets in winter. However, little is known about the effect of switching from outdoor to indoor feeding and husbandry practices on the relative differences in milk composition between organic and conventional systems. There is also limited information on differences in the composition of fat soluble antioxidants in milk from high and low input dairy systems and the few studies available show contradictory results.
Comparison of milk from low input and high input systems
In the present study (Butler et al., 2008) 109 milk samples were collected from 25 commercial farms categorised into three different production systems:
- Conventional, “high input” (HI) farms
- Organically-certified “low input” (O-LI) farms
- Non-organically certified “low input” (NO-LI) farms
Samples of mixed milk were taken from the bulk tank at each participating farm and frozen within 10 hours of sampling and kept at -20°C until dispatched for analysis.
The aims of this study were to:
1) Compare the fatty acid and fat soluble vitamin composition in milk from three UK production systems: certified-organic “low input” (O-LI), nonorganic certified “low input” (NO-LI) and standard “high input” (HI) conventional production systems, during the outdoor grazing period
2) quantify differences in fatty acid and fat soluble vitamin content of milk between O-LI and HI systems, during the winter indoor (conserved forage-based) feeding period
3) identify whether there are differences in milk composition between certified-organic “low input” (O-LI) and non-certified “low input” (NO-LI) systems that use spring block calving systems and graze cows outdoors throughout the lactation (March to October).
Comparison of milk fat composition during the out-door period (fresh forage based diets)
The total fat content was higher in milk from low input, compared to high input herds. When the composition of milk fat was compared the percentage of saturated fatty acids in milk fat was significantly higher (3-5%) in milk from high input farms. In contrast, milk from the 2 low input systems had higher percentages of both monounsaturated (5-11%) and especially polyunsaturated fatty acids (32-39%).
There were no significant differences in the percentages of saturated fatty acids, monounsaturated fatty acids and polyunsaturated fatty acids between the two low input systems.
Comparison of milk fat composition during the indoor period (conserved forage-based diets)
Since the spring block-calving NO-LI and O-LI systems did not produce milk during the indoor period only milk from all year calving O-LI and HI systems was compared.
In contrast to results from the outdoor rearing period, the percentages of total saturated fatty acids in milk fat were significantly higher (4%) and monounsaturated fatty acids significantly lower (10%) in milk from the O-LI system compared with milk from HI systems during the winter indoor period.
The percentage of α-linolenic acid tended to be higher in O-LI milk compared with HI milk (P=0.052). Although the percentages of VA, CLA9 and total carotenoids were numerically higher (by 7, 26 and 15% respectively) in O-LI milk, the changes were not statistically significant.
Comparison of milk fat composition during the grazing period between O-LI and NO-LI spring block calving systems
Apart from CLA isomer C9 (which was present in significantly higher percentages in milk from NO-LI farms), significant differences in fatty acid composition between O-LI and NO-LI spring block calving systems were found only late in the outdoor grazing period (August and October sampling date).
The percentages of total saturated fatty acids and αLA were higher in milk from O-LI systems, while percentages of monounsaturated fatty acids, polyunsaturated fatty acids, VA and CLA9 were higher in milk from NO-LI systems. No significant differences in the percentages of CLA10 and n-6 FAs were detected.
Differences between organic and conventional milk
Milk composition differences (and associated processing, sensory and potential nutritional qualities) between high and low input production systems depend on a range of factors including the stage and length of the outdoor rearing period, feed composition and grassland/grazing management practices used.
Results of the present study suggest that the addition of synthetic vitamin/antioxidant supplements to feed in high input systems has a relatively minor effect on antioxidant concentrations in milk. For example, milk from high input herds, which received high levels of vitamin E supplements, (in our study between 150 and 750 IUs vitamin E/day) contained significantly lower concentrations of total α-tocopherol than milk from farms working to organic farming standards, which do not permit feed supplementation with synthetic vitamins.
While differences in milk composition between organic and conventional milk were clearly demonstrated in this study, there are virtually no animal or human dietary intervention studies into the potential effects of consuming milk from organic and other low input systems on animal or human health. Whether and to what extend milk from low input systems may impact on human health either alone or within the context of an organic food based diet therefore remains unclear, but should be investigated in the future.
Gillian Butler, J.H. Nielsen, T. Slots, C. Seal, M.D. Eyre, R. Sanderson and C. Leifert, 2008. Fatty acid and fat-soluble antioxidant concentrations in milk from high- and low-input conventional and organic systems: seasonal variation. Journal of the Science of Food and Agriculture 88: 1431-1441.