Doug Peterson, Natural Resource Conservation Service (NRCS) state grassland conservationist in Missouri, says stocking density is determined by the animal pounds per acre. For instance, 100, 1,000-lb. cows would be 100,000 lbs. “So, on a half-acre, 100 cows would be 200,000 lbs., while 100 cows on 10 acres would be 10,000 lbs.,” he says.

Jim Gerrish, grazing consultant and owner of American Grazinglands Services in May, ID, says some proponents of mob grazing say stock density must be at least 100,000 lbs./acre.

“I’ve been doing that for years with once-daily moves, but I’m not mob grazing. Others say it must be at least 500,000 lbs./acre to accomplish your goal. It is multiple moves per day and the high-stock density that differentiate mob grazing from other management intensive grazing (MIG) forms,” he says.

“The higher the density, with shorter grazing periods, the more uniform the urine/manure distribution will be. You’re fertilizing the entire piece – dumping more nitrogen back on that pasture. For instance, 100,000 lbs. of animals typically leave 50-55 lbs. of readily available nitrogen on the ground as urine. The higher the stock density, the more uniformly nitrogen is distributed,” Gerrish says.

Animal performance

Mitchell-Innes is a stockman who learned these principles by trial and error in South Africa 14 years ago. He later became a holistic management educator and now preaches the principles worldwide.

He says people must monitor the cattle to know if they’re doing it correctly.  “Otherwise, you’ll go broke,” he says.

The NRCS’s Doug Peterson says large groups of cows confined in small areas become incredibly aggressive grazers.

“You must make sure they have enough forage and only eat the part of the plant that meets their nutritional needs. Dry cows can probably eat 60-70% of the plant, but perhaps only the top 30% of the plant meets the needs of lactating cows or young stockers,” he explains.

Multiple daily moves, watching the degree of utilization and focusing on animal performance are the keys.

 “Many people attempt to get a high degree of plant utilization (70-80%) in an hour or two. But if they’re not giving animals enough total feed during the day, individual performance goes down.”

Dry pregnant cows that are winter-grazing on low-quality stockpiled forage can eat 70-80% of forage and still have good animal performance – maintaining body condition while stretching feed over more days. This is different than mob grazing in summer with pairs or stockers where you need to optimize animal performance, however.

“Your focus should be on keeping daily intake high,” Gerrish explains. If you don’t move them soon enough, they eat a lot at first, then intake tapers off too much before the next move. Layout and design of paddocks and portable fence becomes important for saving time when moving often, he adds.

“If you bunch cattle tightly, don’t limit their plant selection,” says Doug Judy, a Missouri operator. “I’m taking the top third of the plant, then moving cows – regardless of what the pasture looks like. My interns are trained to look at the cattle, watching their left side as they come through the gate – to see whether they left them in the pasture too long. If you keep shortchanging them on gut fill, cows lose weight,” Judy says.