The Telegraph reports on a recent report on the health benefits of milk from grass fed cows. The study shows that what the cows eat affects the quality of the milk produced - I guess that is logical. In the winter the composition of the diet (the cows are inside) means that there is less difference in the nutrient content, but in the summer there is a greater variance.
The Independent reports that grazing provided around 84 per cent of food for cows on organic farms in the summer, compared to 37 per cent for conventionally farmed animals. Silage (preserved grass which is mown in the late spring and summer and then stored and fed to housed cows) will lose some of the nutritional value of fresh grass and with rising fuel prices is now becoming much more expensive to make. There are some conventional systems in the UK that are based on grass fed systems such as those used in New Zealand. It would be interesting to see if the nutritional difference is as pronounced with these systems.
The problem for the consumer is that at the point of purchase it is impossible to differentiate between production systems other than the simplistic "organic" or "conventional" and ultimately how does the consumer know the "time-frame" when the nutritional difference is worth paying for?