I'm surrounded by leased BLM land around here but the parts I've seen are not overgrazed. The lessees are very long term and their livelihood depends on the quality of the forage from year to year. If not overgrazed, cattle have a very positive effect on the landscape. They cultivate the ground with their hooves and excrete fertilizer and seeds. A well grazed lot grows more cow food than an ungrazed one. Even the ranches that focus on elk hunting graze cattle to improve the land for the elk.