What most people don't understand about grassfed farming is it's not just a matter of getting the cows out on grass and making sure they have all the green grass they could eat. It's a matter of having healthy, lush, nourished pastures with dozens of varieties of grasses and legumes such as clover, alfalfa, vetch and so on. I always hear people talk about how modern cows can't be raised on 100% pasture, this is patently false. Usually the people making these claims are either conventional farmers who know cows well, but they only know them under the disgusting, imbalanced CAFO system, NOT artisinal pasture grazing. OR, it's people who have never farmed before and only have a limited working knowledge of the theory, IOW they're not relying on first hand experience.
It doesn't matter how overbred the cow is, if the calf is raised on her mother's milk and then moved directly on to pasture, and that pasture is varied, lush and high brix, then that calf, whether a jersey or a holstein, will be the best possible specimen it can be, it will reach it's genetic potential and you'll see an extremely hardy, nutrient dense, and healthy cow living all on grass.
The case is different for animals raised for a significant portion of their life on grains, supplemented or otherwise. These animals can be very difficult to convert back to grass. I personally feel it can be done, but only if the pasture you're moving them to is AAA quality (nourishing, nutrient dense, high brix, high moisture) and you wean them off the grains slooooowly.
This is based on my last 3 years raising cattle on 100% grass (and poor pasture at that). The cows that had been fed grain supplements for the first few years of their lives at the 'Organic Valley' farm we bought them from(6lbs corn, oats, wheat mix, per day, the rest hay) did well the first year, but then the poor pasture caught up with them and they began to experience some health issues. After I realized the reason for these health issues, I took great pains to take the cows on walks in certain places or through the forest so they could choose the best forage for themselves...and believe me, they have preferences!!
However, all of these cows' offspring thrive on our poor pasture alone and have not had one single health issue to date from any offspring we've had. I would like to see a conventional farm try that (without resorting to drugs, which is a fail by itself), it doesn't exist.
Also I don't have the reference right now unfortunately but, raising cows for their maximum nutrient density on grass is one of those things that requires times and there's not much one can do about that. If you were to go to a CAFO, buy a grain supplemented cow and convert that cow to really lush pasture, it would take about a year (according to the studies I've read in the past and this makes sense to me) to reverse the damage (in terms of the skewed, inflammatory fat profile..and by proxy everything else that would be harmed by high levels of carbs and low levels of biomass and real nutrition to where you could call the animal 100% grassfed. In otherwords, if that animal has been eating grass only for even 6 months, it still won't have the nutrient density it would if it had always been on grass.
Unfortunately it works against us the other direction as well, if you took a 2 year old cow, that had been on mother's milk and pasture it's whole life, and then started supplementing with grain, it would only take about three months for all of those starches, many 1000's of % more than what would be natural in the animals diets (plus it's almost empty calories, more like energy, not nutrition), to skew the nutrient profile from anti inflammatory back to inflammatory (omega 6, and all the other problems that accompany grain feeding).
Of course it's a personal choice how much grain you tolerate in your food, but given that the prolamines from these grains seem to wind up in the meat and milk, probably best to avoid as much as possible. You know what I'm talking about if you're hypersensitive and you can't tolerate any grains at all, you aren't able to eat CAFO meat (at least not healthfully and I believe that is about 100% of reports that I've heard).
I was able to find that chart, and it reads slightly differently than the figure I pointed to initially, 3 months to deplete the vast majority of the omega-3's and increase the level of Omega-6. The fat ratios are just a marker though, damage is being done throughout the animal and you are going to have less of everything good, and more of everything bad, in very broad terms.
The link for said chart...
http://chriskresser.com/9-steps-to-perfect-health-3-eat-real-foodAlso this applies to all farm animals, even if grains/seeds are a natural part of their diets as in chickens and pigs. They should only be eating small amounts of that stuff, the rest of their diet should come from fresh vegetation, roots, bugs, small animals and even meat if it's clean meat (of course why wouldn't you just eat it? The answer is, squiggly bits that you might not normally use, make good nourishment for pigs/chickens. This includes rotting (high) meat.
