Essential Nutritional Information on Grass Fed Beef you must read.
Total Fat and Calories
Beef from pasture-fed cattle has a lower fat content and has less calories than beef from grain-fed cattle. If the meat is very lean, it can have one third as much fat as a similar cut from a grain-fed animal. As you can see by the graph below, grass-fed beef can have the same amount of fat as skinless chicken, wild deer, or elk. Research also shows that lean beef actually lowers your “bad” LDL cholesterol levels.
Meat from grass-fed animals has two to four times more omega-3 fatty acids than meat from grain- fed animals. Omega-3s are called “good fats” because they play a vital role in every cell and system in your body. Of all the fats, they are the most heart-friendly. People who have ample amounts of omega-3s in their diet are less likely to have high blood pressure or an irregular heartbeat. Remarkably, they are 50 percent less likely to suffer a heart attack. Omega-3s are essential for your brain as well. People with a diet rich in omega-3s are less likely to suffer from depression, schizophrenia, attention deficit disorder (hyperactivity), or Alzheimer’s disease.
Another benefit of omega-3s is that they may reduce your risk of cancer. In animal studies, these essential fats have slowed the growth of a wide array of cancers and also kept them from spreading. Although the human research is in its infancy, researchers have shown that omega-3s can slow or even reverse the extreme weight loss that accompanies advanced cancer and also hasten recovery from surgery.[6,7]
Omega-3s are most abundant in seafood and certain nuts and seeds but they are also found in animals raised on pasture. The reason is simple. Omega-3s are formed in the chloroplasts of green leaves and algae. Sixty percent of the fatty acids in grass are omega-3s. When cattle are taken off omega-3 rich grass and shipped to a feedlot to be fattened on omega-3 poor grain, they begin losing their store of this beneficial fat. Each day that an animal spends in the feedlot, or fed grain in the paddock, its supply of omega-3s is diminished. The graph below illustrates this steady decline.
Conjugated Linoleic Acid (CLA)
Meat and dairy products from grass-fed ruminants are the richest known source of another type of good fat called “conjugated linoleic acid” or CLA. When ruminants are raised on fresh pasture alone, their products contain from three to five times more CLA than products from animals fed conventional diets. (A steak from the most marbled grass-fed animals will have the most CLA ,as much of the CLA is stored in fat cells.)
CLA may be one of our most potent defences against cancer. In laboratory animals, a very small percentage of CLA-a mere 0.1 percent of total calories-greatly reduced tumour growth.  There is new evidence that CLA may also reduce cancer risk in humans. In a Finnish study, women who had the highest levels of CLA in their diet, had a 60 percent lower risk of breast cancer than those with the lowest levels. Switching from grain-fed to grass-fed meat and dairy products places women in this lowest risk category.
In addition to being higher in omega-3s and CLA, meat from grass-fed animals is also higher in vitamin E. The graph below shows vitamin E levels in meat from: 1) feedlot cattle, 2) feedlot cattle given high doses of synthetic vitamin E (1,000 IU per day), and 3) cattle raised on fresh pasture with no added supplements. The meat from the pastured cattle is four times higher in vitamin E than the meat from the feedlot cattle and, interestingly, almost twice as high as the meat from the feedlot cattle given vitamin E supplements.  In humans, vitamin E is linked with a lower risk of heart disease and cancer. This potent antioxidant may also have anti-aging properties.
Grass-fed meat has a similar fat profile to wild game
When cattle are free to forage on their natural diet of grass, their meat is almost as lean as wild game. The graph below shows that grass-fed beef has an overall fat content similar to wild animals such as deer.
This second graph shows that grain-fed beef has a much higher ratio of omega-6 to omega-3 fatty acids than wild game or grass-fed beef. A high ratio of omega-6 to omega-3 fatty acids has been linked with an increased risk of cancer, cardiovascular disease, allergies, depression, obesity, and auto-immune disorders. (Simopoulos and Robinson, The Omega Diet, published by HarperCollins in 1999.) A ratio of four or lower is considered ideal. The ratio in grain-fed beef is more than 14 to 1. In grass-fed beef, it is approximately two to one.