Like moat humans need ~2000 calories TV just exist, what's a cows bmr? I looked it up and animals are listed as Mcal, 1Mcal = 1,000,000. 1 human calorie is = 1,000. so 2,000 human calories is 2,000,000. The PDF I found ranges a 1000lb cow needing 18 Mcal per day for non lactating and up to 28 Mcal for lactating. That's 18,000 calories per day in fees/graze.  There's no way humans eating plants as primary diet is more harmful and less efficient.