Some breeds absolutley do need grain for finishing. The blonde d'aquitaine being the most obvious example. They were selectivley bred for a high grain diet when grain was cheap as a result have small rumens and need an extremely high energy diet in order to finish (linseed etc). My father inlaw used to do a couple pf heifers a year. U+2 600kg carcasse sold for over 3000€.No no no, often get told that some breeds will not do of grass and need feeding grain, you must be mistaken
Even so, the national average for the fat score is 2.
Adapted genetics are extremely important.