verbs - Is "There was a herd of cattle eating grass" a valid sentence?

This is just a simple question, but I was wondering about this. I would think "herd" is the subject here, and since a herd can't eat (only an individual cow can), would I need to rearrange this sentence to be accurate?

If this is a correct sentence, what if I changed it to "There was a herd of cattle all eating grass"? Does that make a difference?