Summer milk has been estimated to contain 1.6 times as much of which vitamin compared to winter milk?

Summer milk is known to contain higher levels of certain vitamins due to changes in the cows' diets and exposure to sunlight. The correct answer is Vitamin A. During the summer months, cows typically graze on fresh green pasture, which is rich in carotenoids, the precursors to Vitamin A. This increased intake from fresh forage leads to a higher concentration of Vitamin A in the milk produced. Moreover, Vitamin A is fat-soluble, meaning that it can accumulate in the fat of dairy products, leading to enhanced levels in summer milk.

In contrast, during the winter, cows are often fed stored feed such as silage or hay, which may have lower carotenoid content, resulting in diminished levels of Vitamin A in milk. This seasonal variation highlights the nutritional impact of grazing and the natural changes in cow diets throughout the year. Other vitamins listed, while important, do not show the same specific seasonal differences in concentration as Vitamin A does.