Like produce, milk quality can vary with the season and year. Dairy cows' daily diet, much of which comes from plant forage, determines the nutritional makeup of their milk, so when their food lags in quality, so too does their output. And a new study shows that conventionally produced milk is more prone to these unfavorable seasonal shifts than organic milk.
Earlier research had shown slight benefits in organic milk's nutritional profile when it was tested on the farm. "Whereas on the farms the benefits of organic milk were proven in the summer but not in the winter, in the supermarkets it is significantly better quality year round," Gillian Butler, of the Nafferton Ecological Farming Group at Newcastle University and study co-author, said in a prepared statement.
Butler and her team sampled 22 brands of U.K. milk four times between 2006 and 2008 and found that the organic milk brands had far less seasonal and annual variability. Some of the conventional milk brands, for instance, tended to have higher concentrations of saturated fats and lower levels of beneficial ones, such as omega-3 and polyunsaturated fats after poor growing seasons.
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