this is just my .02. We are very fortunate to be sponsored by Brandt Beef in California, they raise Holstein Steers which are fed a diet of steamed corn mash and chopped Sudan grass for at least 365 days.
This diet creates a different fat profile and marbling of the beef in general, it has been explained to me that strictly grass fed steer are normally leaner than corn or blended feed beef, this leads to less fat, which translates to less colagen to breakdown, I have noticed that when I have cooked a grassfed brisket it tends to be dryer, and shrinks more, i also have seen them finish in as little as 6 hours. below is a picture of the Brandt Point
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