When there is a market, someone will sell to it, even if it does not make much sense. So you can purchase organic pineapples and non-GMO rock salt if it makes you feel better.

In Europe, most genetically modified foods, as European politicians define them, are banned but cows eat GMO feed. The cows can't tell the difference nor have studies shown any difference in milk production or meat. Vermont passed a GMO labeling law but made sure to exempt cows so that the $300 million company run by the primary funder of the Just Label It campaign could still use milk from Vermont cows fed GMO grain in organic yogurt.

Yet despite all that, some groups are endorsing studies claiming a benefit to organic milk. What does the science say? A new review finds what most in science know; with over 25,000 open access journals, many of them competing for customers, anything can get published. 

A recent review of almost 200 publications concluded that studies claiming to be controlled have still been largely ambiguous - no surprise when some organic proponents doing studies claim 'mouth feel' as scientifically valid.  And organic proponents aren't doing comparisons that would pass skepticism among their comparison if they came to the conclusion that conventional milk was superior. 

"When comparing organic and conventional milk composition (especially milk fatty acids), previous studies have generally compared organic dairying with milk produced from grass-fed cows to conventional dairying with milk produced from concentrate-fed cows. The differences in milk composition observed are actually due to the different diets of the cows (i.e. pasture versus concentrate feeding) rather than organic versus conventional farming systems," according to lead investigator Don Otter, PhD, Senior Scientist, Food&Bio-based Products, AgResearch Grasslands Research Centre (New Zealand).

Because there are many factors that affect milk composition, it is difficult to control for all of them when comparing organic to conventional milk production. According to the investigators, "The term 'organic' when applied to dairying is not universal, and to a large extent, is defined simply by regulations that differ from one country to the next. 'Conventional' basically is anything that is not 'organic.' However, in most parts of the world, conventional dairying is associated with high levels of grain feeding, the use of cow breeds which produce high milk volumes, and the application of large amounts of fertilizer ('high input' farming), while organic dairying is tied to pasture and forage feeding, lower amounts of fertilizer application, and the use of mixed or minority breeds ('low input'). The vast majority of differences reported between organic and conventional milk come from what cows are fed and their breed, and is not anything unique to being organic or conventional in itself."

Therefore in terms of nutrients in milk, there is nothing distinct about organic milk that makes it unique from conventionally produced milk once the different factors that influence milk production are compared or adjusted for. If animal genetics, health, breed, diet, management, or environment differs, then so will the composition of the milk produced.

Published in in the Journal of Dairy Science.