Ultra-high stock density grazing, also called mob grazing, is a practice where a large concentration of animals are restricted to graze a small area, usually for a very short period of time. While there’s no strict definition on the size of herd or smallness of the area, some folks suggest at least 300,000 lbs. of animals/acre, or about 200 cow-calf pairs/acre, 1,000 pairs on five acres, or 50 pairs on a quarter acre. A few mob grazing experts have gone more than three times higher, to more than 1 million lbs. of animal/acre, says Bruce Anderson, University of Nebraska Extension forage specialist.