Jacob Holm Nielsen, PhD, and Tina Slots (formerly Lund-Nielsen), PhD, both of the Danish Institute of Agricultural Sciences, explained in their Jan. 2005 paper "Healthier Organic Livestock Products: Antioxidants in Organic and Conventional Produced Milk," presented at the First Annual European Union Project Quality Low Input Food and Soil Association Annual Conference:

“Organically reared cows, which eat high levels of fresh grass, clover pasture and grass cover silage, produced milk which is on average 50% higher in vitamin E (alpha tocopherol), 75% higher in beta carotene (which our bodies convert to vitamin A) and two to three times higher in the antioxidants lutein and zeaxanthine than non-organic milk… In addition, we found higher levels of omega 3 essential fatty acids.”

Jan, 2005