There is currently a lot of interest in mob grazing, so let me be perfectly clear. I have no idea when a “mob” specifically becomes a mob. In Australia, the term mob is synonymous with what we would call a herd, but generally when we refer to mob grazing in Canada what we are talking about is extreme or ultra-high stock density (UHD) grazing. A rough guideline for mob or ultra-high density is 100,000 or more pounds of animal per acre. To provide a picture of what that might look like, if you have 1,250-pound cows, you would have 80 or more cows on a single acre at a specific point in time.
Let’s start from the beginning. Stocking rate can be thought of as matching the cattle to the production of an entire pasture. If a pasture produces enough forage for 10 cows during the growing season, then the appropriate stocking rate would be 10 cows. Stock density is the number of cows per acre at any one time. No matter what stock density we have, we still want to match the stocking rate to the available forage production.
Here’s where it gets tricky. By confining the area available to the herd, usually using electric fence of some sort, the stock density can be increased (more cows on a small area at a specific point in time). Conversely, this means that there are no cows on the rest of the pasture and the grass can be growing without interference.
Let’s use the earlier picture of 80 cows on an acre of grass. Intuitively we know that those cows will run out of feed in a relatively short time. This reflects the stocking rate of that acre and brings us to the second point behind UHD grazing. As we increase density, we take down the production more quickly and thus must move cattle off of that acre more quickly as well. If we use that 100,000 pounds of animals with a dry matter intake of three per cent of body mass daily, they would consume 3,000 pounds of dry matter. In grass that is 85 per cent moisture that equates to 20,000 pounds of grass. If we follow the ‘take 1/2″, leave 1/2″ stocking rate rule of thumb, that works out to 40,000 pounds of forage (as fed) consumed by a 100,000-pound mob every day. Hence the reason for all those moves.
Remember, the idea behind UHD grazing is NOT to take everything off of that acre. The idea behind high-density grazing is to utilize the plants extremely evenly rather than letting the cattle pick and choose, and to spread the manure and urine evenly across the landscape. Further, this ultra-high density provides hoof action to ensure good soil contact with the leftover plant material, fuelling the soil microbiota and facilitating decomposition and nutrient cycling. Over time, these effects are what increases the stocking rate of the pasture.
One factor of mob grazing that is often discussed is that of individual animal performance. A goal of mob grazing is to optimize production per acre rather than per animal. This is a foundational shift for a lot of folks that are cow-centric and would like to see every animal achieve its maximum potential. A way to think about it is if you planted one canola plant every square foot to give that plant the best opportunity to maximize its production rather than seeding 10 plants per square foot to maximize production per acre.
UHD grazing can be pretty intense. There are some folks moving cattle every four hours or less for exactly the reasons discussed above. Even with technology such as Batt latches that can be set to open gates at specified intervals, this level of supervision is probably beyond most of our aspirations, but the concepts still apply at any scale of intensity. By concentrating animals you are allowing much of the pasture to rest. By increasing stock density to some level you are ensuring more even utilization of the plants and evening out the nutrient cycling across the landscape. Improving the soil contact of that remaining plant through trampling effect more rapidly increases organic matter in the soil and can begin to build that soil profile.
While ultra-high density grazing may not be for all of us, for many of us, a little bit of a mob mentality could go a long way.