According to a recent Wisconsin survey questioning producers who practice some form of mob grazing, their cattle stock densities average from 50,000 to 200,000 lbs of cattle live weight per acre.
It’s been touted as an efficient way to use all available forage while evenly distributing nutrients, controlling weeds and improving soil health. High-profile producers are holding seminars and taking speaking engagements to tell how they’re using mob grazing, also called ultra-high stock density grazing or tall grazing.
But scientific proof of mob grazing’s benefits has been sorely lacking. Only the past few years have researchers begun to study this somewhat misunderstood grazing management method. And it hasn’t been easy.
First of all, mob graziers themselves are reluctant to define the practice, says Anders Gurda, University of Wisconsin (UW) graduate student at Madison. One of several researchers whose work will be profiled here, Gurda admits to having cornered well-known, successful mob graziers, asking them their interpretations of the practice.
“I’ve been coming up to these guys and kind of twisting their arms, asking, ‘If you had to just shout out a definition of mob grazing in terms of stocking density, what would you say?’ All of them say, ‘I’m hesitant to do that.’ ”
They’re wary because mob grazing involves more than “mobs” of cattle frequently moved from one tall-forage pasture area to another, with long pasture rest periods between grazings, Gurda says.
That definition implies “a static application of tons of cows and that’s it. A lot of people want to dismiss it because they see it as that. They don’t see it as something that’s really dynamic and responsive.
“The best definition I have heard is something like, ‘a strategic deployment of an increased stocking density for a stated purpose,’ ” he says. “The producers I’ve talked to who I feel are doing it well are the ones saying, ‘I use it as a tool.’ ”
A mob strategy “needs to be very elastic, very responsive to what you are seeing. Say, during the spring flush, you can afford to stock a half a million pounds or more (of live cattle weight per acre). There is a lot of forage there, and you’re trying to get through it and not have to mow. Whereas, during the summer slump sometime in July and early August, when production really takes a hit, you might strategically destock to 100,000 lbs/acre or less,” reports the Wisconsin grad student.
Other researchers, from Virginia to Pennsylvania to South Dakota, agree that mob grazing should be used as part of an overall pasture grazing strategy. They include Jim Russell, the Iowa State University animal scientist who, for two years, studied the effects of season-long mob grazing using up to 440,000-lb/acre stocking densities and moving cattle up to four times a day.
“We saw no improvement to season-long mob grazing in terms of animal production, legume establishment or soil organic matter (compared to strip and rotational grazing),” he says. “But we think that, as a strategic management tool for specific objectives, it has a role.”
He’s tested short-term, strategic mob grazing as a means to knock down grass competition and increase the percentage of clovers in a pasture. “We’ve been very successful with that; we’ve gotten some grass areas the year after we mob grazed close to 40% legume.”
To increase the legume percentage, Russell recommends mob grazing something like 10% of a pasture already containing legume seed in the soil, then rotationally grazing the rest. The next year, a second 10% of pasture could be mob grazed and so on.
Fortunate to have Leopold Center for Sustainable Agriculture funding, Russell has also proved that mob grazing disturbances to pasture help improve perennial grasslands, such as Conservation Reserve Program-enrolled or recreational land, for wildlife habitat.
Mob grazing techniques of nine South Dakota and five Nebraska beef producers are being studied by South Dakota State University (SDSU) and University of Nebraska specialists.
“We’re documenting what’s happening,” states Sandy Smart, SDSU range scientist. “Producers are doing their own thing; we’re learning from all the different ways they are doing it. They may be mob grazing a month or two months out of the year and then they go back to some sort of a regular rotation where they may (move cattle) once a week or every 10 days.”
He and other researchers are looking at the amount of forage consumed and trampled. “Then we’re following that up through soil sampling and tracking the material that gets trampled, how that translates to increasing soil carbon and how it affects water infiltration and nutrient cycling.”
The range scientist is hoping that his team’s results will offer “a better understanding throughout the Great Plains of what’s happening on these different ranches and as people are using different stock densities.”
So far, ranchers in higher-rainfall areas are having better success trampling forage, which “helps increase water infiltration and then goes toward increasing carbon sequestration and soil health,” Smart theorizes. “It’s harder to get new litter on the ground in farther western environments where they have less rainfall and grass production.
“But that’s where stocking density comes into play. It takes a higher stock density to have more trampling, and that becomes a challenging issue in areas that don’t produce as much grass. Then you have to be moving the livestock more frequently, on the order of several times a day.”
Many of the South Dakota ranchers are mob grazing cow-calf pairs at least once a day on land formerly planted to crops that they hope to improve. “And in Nebraska, they’re targeting hay meadows that would traditionally be hayed. They’re trying to use mob grazing to increase the efficiency of the harvest.”
Their stocking densities range from 20,000 lbs/acre to 200,000.
Other researchers are looking at mob grazing economics, including labor costs. But Smart mentions benefits not easily measured. “When you’re moving your cattle every day, you also are noticing things — you may spot animals that are sick quicker than others would. If a bull comes up injured, you can treat him.
“We’re also noticing that the cattle may be eating plants that they may normally not eat — weeds. In a traditional grazing system, they may have left those plants alone. But in mob grazing, they pretty much eat it all.” A weed specialist is examining how the strategy affects weed populations.
Mob grazing’s effects on Canada thistle, a problem weed in Wisconsin pastures, are being studied through trials conducted by Gurda and Mark Renz, UW Extension weed specialist. The three sites being used represent varied pasture composition and a diversity of grazing animals: a bred-heifer dairy herd, a heifer-and-stocker herd and a beef cow-calf herd.
At each site, Canada thistle control will be assessed four ways: on a rotationally grazed control area, on pasture rotationally grazed after herbicide is applied, on an area mob grazed for one year followed by rotational grazing and on pasture mob grazed for two years.
“We’re hypothesizing that decreased selectivity, as well as increased hoof impact that often creates a thick ‘mulch’ of trampled forage, might negatively impact the Canada thistle in the research plots,” Gurda says.
The grazing trials are in their second field season; results will be available next spring. At the same time, he’s compiling results of a survey asking rotational graziers’ perceptions of mob grazing. Part of the reason is to figure out the best way to disseminate what they’ll learn from their Canada thistle work.
“This has told me that we need to be at as many pasture walks and producer-to-producer conferences as possible,” he says (see "What Is Mob Grazing?").
Earlier Wisconsin research could be of use to mob graziers, says Geoff Brink, research agronomist at USDA’s U.S. Dairy Forage Research Center.
“We were looking at grasses that were grown to maturity, as a mob grazier would. But we wanted to look at residue height, or the amount of grass that remains after the cattle are removed from pasture. We wanted to see how that affected regrowth and seasonal yield distribution and other things, such as forage quality.”
His results showed that leaving some residue, rather than letting it all be consumed, is beneficial to regrowth. However, the grazing experiment didn’t confine animals, so their manure wasn’t completely deposited where they grazed — which is considered an important facet of mob grazing, Brink says.
Mob grazing appears to be improving pastures on two Virginia sites, says Ben Tracy, grassland ecosystem management specialist at Virginia Tech.
“After mob grazing, the regrowth has been impressive and looks a lot better than our other demonstrations where we’re doing continuous grazing. There are a lot fewer seedheads, less rank vegetation, and it looks like a healthier, more nutritious pasture.”
This past May, Tracy started measuring plant and soil responses to mob grazing compared to continuous and rotational grazing. Providing water for cattle can be challenging in mob grazing systems; the Shenandoah Valley site didn’t have it placed so manure and urine were evenly distributed, he says.
“We’re going to try to modify that to get a water source to each of the strips where we mob graze and make the area smaller. That will increase our stocking density.”
He hopes it will be comparable to the 100,000-lb/acre rate used at the second site, near Blacksburg.
“One of our objectives with mob grazing is to graze about half of the forage, trample about 40% and leave about 10% standing. We did a detailed visual examination after the mob grazing to see how well we did. We seem to be hitting the mark pretty well.”
On both sites so far, mob grazing has kept down weeds.
“Before we started mob grazing, there was a lot of broomsedge,” he says of one of the sites, both of which are composed of tall fescue with orchardgrass and bluegrass.
At the other site, horsenettle and a woody shrub called coralberry were problems. After mob grazing, there appeared to be fewer of the troublesome weeds at both sites, while continuously grazed areas were infested with them.
Concerned by new dairy graziers’ interest in mob grazing, Mena Hautau corralled five certified-organic dairy producers using a form of the technique. Then she asked to study them.
What the Penn State Extension educator in Berks County found was that the producers adapted the mob grazing strategy to suit dairy-forage quality. They also like to refer to the method as “tall grazing” or “high-density stocking.”
“They let these forage plants flower a little bit, but don’t let them go to brown,” Hautau says. Essentially, the forage’s quality is equivalent to that put up as baleage or haylage.
Pre- and post-grazing forage samples were taken on each dairy during two tall-grazing sessions per year over two years, says Hautau, who pooled grant monies and knowledge with Kathy Soder at the USDA-ARS Pasture Systems Research Unit at University Park, PA.
Stock densities ranged from 44,000 to 337,000 lbs/acre, and cattle were moved two or more times a day. Forage was rested from 40 to 78 days.
“Farmers told us they moved cattle more frequently if the forage quality was not ideal, leaving more grass as residue.” Some tried to leave 25% standing, 50% eaten and 25% trampled, while others tried to graze so 30% of forage was remaining. Some, Hautau says, left 25-50% of the forage.
“We took forage samples of a paddock and followed that paddock through the rotation. We looked at what the animals were actually eating, how deep into the canopy they were going, that sort of thing.”
A “mini-drought” in the middle of the 2012 growing season caused them to tall-graze over-mature pastures that consisted mostly of orchardgrass with clovers mixed in.
Crude protein averaged 20% on a dry matter basis during that year’s June-July grazing session and improved to 28.5% by the September-November grazing. Neutral detergent fiber (NDF) averaged 52% to 34% from the first to the second set of grazings, and net energy at lactation (NEL) ranged from 0.61 to 0.73 Mcal/lb dry matter from the first to the second pasture grazing session.
Hautau is now compiling this spring’s data. She’s informing new graziers that the system requires experience.
“If farmers are good managers in grazing, they can probably do this. But it’s a hybrid system.” It’s not the mob grazing system beef producers are using, she stresses.
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