Newcastle researchers found that milk collected during a cooler summer and the following winter had significantly higher saturated fat content and far less beneficial fatty acids than in a warmer year.
One solution, though obviously expensive, is to switch to so-called organic milk. The researchers found that organic supermarket milk showed higher levels of nutritionally beneficial fatty acids compared to less expensive milk regardless of the time of year or weather conditions. Low levels of omega-3 and polyunsaturated fatty acids were discovered in some regular milk brands, which they say are indicative of a diet low in fresh grass. These samples also showed evidence of the cows being supplemented with a saturated fat product derived from palm oil.
The organic brands they studied showed a reliance on forage, especially grazing, and an absence of nitrogen fertilizer, which they say led to more red and white clover, which have been said to alter the fatty acid intake and composition of milk. While protein, antioxidants, vitamins, minerals and some mono and polyunsaturated fatty acids in milk are considered beneficial, saturated fatty acids are believed to have a negative effect on human health.
"By choosing organic milk you can cut saturated fats by 30-50 percent and still get the same intake of beneficial fatty acids, as the omega-3 levels are higher but omega-6 is not, which helps to improve the crucial ratio between the two," said Newcastle's Gillian Butler, who led the research.
More a concern is their surprising link between milk quality and our changing climate. Their results suggest that if U.K. residents continue to have wetter, cooler summers then farmers may have to rethink their current dairy practices - though regular milk is the same milk a hundred years of Brits grew up drinking in a cool, wet British climate.
The researchers looked at the quality of milk in supermarkets across North East England at varying times of year over a two-year period. They concluded that organic brands of milk available in supermarkets are higher in beneficial fatty acids such as CLA and omega-3 fatty acids in summer (as in their previous research) and winter (where previous research showed that the difference in the winter was not as noticeable).
They noted a difference between the milk bought in the first sampling period (July 2006 and January 2007) and corresponding times a year later. The second set of samples, following a particularly wet summer in 2007, was higher in saturated fat and lower in beneficial fatty acids. In North East England, for example, the summer of 2007 was particularly wet, with approximately 30 per cent higher recorded rainfall and 12 per cent lower temperatures compared with 2006.
"These conditions may affect the cows' behaviour, reducing grazing intake and milk output," said Butler. "Farmers also often increase supplementation with concentrated feeds or conserved forage to maintain milk yields in these conditions."
During the region's main silage making period (late May until the end of July) rainfall in 2007 was three times higher than the previous year, which also made for poorer quality silage and therefore the need for greater supplementation to compensate in winter diets.
"If these weather patterns continue, both forage and dairy management will have to adapt to maintain current milk quality," said Butler. "The higher levels of beneficial fats in organic milk would more than compensate for the depression brought about by relatively poor weather conditions in the wet year."
The study is published in this month's Journal of Dairy Science.
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