At the American Forage and Grassland Council’s annual meeting in Roanoke, Virginia, this past January, I was asked to summarize and present the scientific literature on mob grazing. This article provides a distilled version of that research summary.
Introduction and Terminology
Rotational grazing (RG) has been promoted by many land-grant universities and USDA-NRCS (Natural Resources Conservation Service) for a number of years. Substantial research has shown rotational grazing to have many benefits, including improvements to soil fertility and health, reductions in hay feeding, increased stocking rates and greater profitability. Mob grazing (MOB) is a more intensive type of rotational grazing.
A MOB system is characterized by ultra-high stocking densities (greater than 100,000 pounds of bodyweight per acre), short durations (one day or less between rotations) and long rest periods (usually at least 45 days of growth). For example, a cattleman may have 200 heifers that each weigh 1,000 pounds on a 1-acre tall fescue-based paddock for eight hours (0.33 days), and those animals may not rotate back to this area for 60 days.
In this discussion, a MOB system is defined by the characteristics above, and an RG system refers to stocking densities less than 100,000 pounds of bodyweight per acre and one- to 20-day stays in a paddock before rotating to the next one. Rest period is left undefined, since it varies during the season and with forage species.
To present the subject, a shorthand notation that Dr. Woody Lane and I have developed (see Dr. Lane’s article in the June issue of Progressive Forage) will be used. For instance, the example of mob-grazed heifers mentioned above could be summarized with the shorthand MOB,0.33,200K (note the lack of spaces).
The first term (MOB) represents the system, the middle value indicates the fraction of a day or number of days the stock spend grazing a paddock and the last value indicates the stocking density. Similarly, a rotational grazing (RG) system where those same 200 heifers grazed a 10-acre, tall fescue-based paddock for three days before being rotated to the next 10-acre paddock could be described with the shorthand of RG,3,20K.
Forage and Animal Measures
Forage quality – One of the most frequent questions about mob grazing is the impact that those long rest periods have on forage maturity and, therefore, forage quality. In studies in Nebraska and Michigan, there was generally no consistent impact on forage quality in the spring and early summer. However, forage quality differences were more common in the latter half of the grazing season.
In Michigan, perennial cool-season grass pastures had forage up to 30 percent lower in protein and 15 percent lower in digestibility when managed under a MOB,0.33,100K system compared to an RG,1,30K system. Despite being lower in nutritive value, dry matter intake rates were similar in both systems.
Animal performance – Of course, a fundamental question is whether or not mob grazing impacts animal performance. In the cool-season grass pastures in the Michigan research, beef cow weights did not differ between MOB,0.33,100K and RG,1,30K systems. In a preliminary report on warm-season, grass-based pasture research in Arkansas, an RG,1,50K system – meant to represent a MOB-like system common in their region – resulted in a significant loss of body condition in cows compared to an RG,6,5K system.
However, they observed no significant differences in cow or calf weight and blood serum indicators of stress were also not different between the treatments. In contrast, researchers in Nebraska found that yearling steer gains averaged 0.4 pounds per head per day on a MOB,0.5,200K while an RG,10,5K system produced 1.5 pounds per head per day (Figure 1).
Animal activity – Researchers in Nebraska used pedometers similar to the fitness monitors that many people now wear on their wrists. They found that cattle grazing in a MOB,0.5,200K system took 5,551 steps per day, while cattle in an RG,15,7.5K took an average of 1,592 fewer steps each day. Their observation was that this was likely the result of having long (300 feet) and narrow (12 feet) rectangular paddocks where animals were stocked so densely they had to regularly move around other cattle to find enough forage.
In a follow-up study, they noted that square paddocks reduced the amount of walking in the MOB,0.5,200K system, but that there was still a significant increase in walking compared to the RG,15,7.5K.
Species shifts – Those who use mob grazing report significant shifts in the species that make up their pastures. Researchers have not consistently observed such shifts. There have been minor species shifts reported in Michigan, where they tended to lose shorter-growing grass and legume species in the MOB,0.33,100K relative to the RG,1,30K systems.
In both systems, they lost bluegrass from the mix. Reports out of Iowa where they compared two mob grazing intensities, MOB,0.25,500K and MOB,1,110K, also only found subtle shifts away from shorter-growing pasture species compared to a non-grazed control. Similar results were reported by researchers in Nebraska comparing a MOB,0.5,200K, an RG,15,7.5K and an RG,10,5K system.
Each of the researchers stated the variability in species diversity they observed seemed to have more to do with weather events than grazing management.
Consumption versus trampling – The efficiency of forage use is often the most hotly debated aspect between advocates for rotational and mob grazing. In Nebraska, the MOB,0.5,200K resulted in 56 percent of the forage being trampled while 33 percent disappeared (likely consumed; Figure 2). In contrast, the RG,10,5K system resulted in only 19 percent being trampled and 44 percent being consumed.
Similar reports came from the Michigan research. Additional research in Nebraska examined incremental increases in MOB stocking densities of up to 750,000 pounds of bodyweight per acre and found the rate of trampling did not increase at stocking densities greater than 100,000 pounds of bodyweight per acre.
Impacts on the Soil
Soil temperature and moisture – Proponents of mob grazing have observed that the trampling of forage keeps the soil from heating up in the sun and helps to keep the soil from losing moisture. Research in Michigan, however, found that soil temperatures were lower and soil moisture was higher in the RG,1,30K relative to the MOB,0.33,100K systems.
Conclusions from their research must be drawn cautiously until more replications of these treatments can examine these effects over more soil types and landscape positions.
Mulch on the soil surface – With all that trampling of forage, one would assume that a mob system would result in more residue on the soil surface. However, work in Nebraska indicated that the MOB,0.5,200K resulted in an average of 2 percent loss in litter mass, which was similar to the non-grazed control.
Meanwhile, the RG,15,7.5K and RG,10,5K systems resulted in a 7 to 12 percent increase in residue on the soil surface (Figure 3).
Measures of residue on the soil surface in the four subsequent years of that Nebraska trial showed no difference between treatments. They also found there was no increase in root production or litter decomposition rates between those grazing systems.
Soil compaction – With those ultra-high stocking densities, some worry that excessive soil compaction may occur as a result of the hoof traffic. Here again, the research does not provide clear answers. In an Iowa study, MOB,0.25,500K and MOB,1,110K systems resulted in no difference in penetrometer resistance (i.e., more soil compaction). In Michigan, soil compaction in the RG,1,30K treatment tended to be approximately 10 percent lower than in the MOB,0.33,100K system.
Soil organic matter – For those who practice mob grazing, one of the major reasons they give for employing the system is they want to improve soil organic matter (OM) and the biological activity of the soil. This is certainly a noble goal. But does mob grazing increase soil OM faster than the lower stocking densities in more common rotational grazing systems?
Very limited research data are available on this aspect, but the research in Michigan found that soil OM was higher in the RG,1,30K relative to the MOB,0.33,100K system at each increment in a 12-inch soil profile. Again, one should be cautious with conclusions until this research can be replicated across other soil types and landscape positions.
Still, it is worth noting that the rate of soil OM buildup in the soils where the RG,1,30K system was put in place are generally in line with the rate of soil OM increase we have observed on pasture-based dairies in Georgia. Those dairies typically operate a RG,1,50K system, and our on-farm research has repeatedly observed that soil OM increases at a rate of up to 0.30 to 0.33 percentage points each year for at least eight to 10 years after converting from cropland.
Greenhouse Gas Emissions
Carbon footprint – The discussion about soil OM buildup in the soil is a great segue into discussions about greenhouse gas emissions and the “carbon footprint” of these systems. The research in Michigan addressed this aspect in great detail.
Table 1 presents their estimates of greenhouse gas emissions from the pasture and from the livestock on an animal unit basis. The largest difference can be found in the amount of carbon dioxide, nitrous oxide and methane emissions from the soil on an animal unit basis.
The greenhouse gas emissions from the soil of the RG,1,30K pastures were 50 to 70 percent less than the MOB,0.33,100K system per animal unit. This is largely because the RG,1,30K and MOB,0.33,100K systems in their experiment were different in the stocking rate.
True, the stocking density at any one point in time on the MOB,0.33,100K system had over three times more animals per acre on the areas being grazed than did the RG,1,30K system. But stocking density is not the same as stocking rate. The stocking rate over the whole season and across all of the grazeable acres in the RG,1,30K system was 250 percent higher than the MOB,0.33,100K system.
Methane emissions from animals in each system were not substantially different, but because more animals could be stocked on the RG,1,30K system, its total carbon footprint was over 50 percent less per animal production unit than the MOB,0.33,100K system.
After all is said and done, no farm production system is sustainable if it is not profitable. Livestock economists from South Dakota State University examined the multiple years of production data from the grazing research in Nebraska to compare the average profitability of the MOB,0.5,200K, RG,15,7.5K and RG,10,5K systems (Table 2).
They found the MOB,0.5,200K system resulted in the lowest average net return and the most variability in profit from year to year. In their analysis, the most profitable and least variable system was the RG,10,5K grazing management. They estimated that approximately 75 percent of the time, producers operating an RG,10,5K system would have a net return greater than $25 per acre. In contrast, the probability of a net return greater than $25 per acre in the MOB,0.5,200K was estimated at 12 percent.
Weaknesses and Data Gaps
Grazing research is very challenging, and no study can answer all the questions. The research published to date is merely a good start. There is still a lot of research that needs to be done, and on-farm data collection should be a point of emphasis. Most comparisons have been conducted on cool-season, perennial grass-based pastures.
Only some of the research has used native grasses and only one has examined this practice on introduced warm-season perennial grasses. Grazing strategies that work in one area may not work well elsewhere.
More importantly, most of the studies to date set the stocking rate equal across treatments. Research has not yet determined if rotational and mob grazing management systems differ in their optimal stocking rates or in carrying capacity over the long run.
Fundamentally, the farmer or rancher needs to know what grazing management strategy will result in the most marketable product per acre while minimizing environmental impact and sustaining an enjoyable livelihood. As yet, the data are too sparse to conclude mob grazing will meet this goal. But all of the early evidence suggests that a well-managed rotational grazing system with frequent moves and moderate stocking densities is more likely to reliably meet this goal.
This article originally appeared in Progressive Forage Grower.
A video of the full presentation is available here. The cited literature can be found in that video or downloaded here if you would like to dig deeper into the details. Please note that none of the data summarized on this subject is by Dennis Hancock. In this article, he reports only on the conclusions of others. If you have questions about those conclusions, contact the authors of those studies.
We welcome your constructive thoughts and comments below.
We rotate once per day with 45k#. We did that in the summer and are doing it now. Seems to be working. I need to get a full year experience under my belt to see if it will work this spring.
I am very glad to see RG still viable in this Michigan study. My cool season grasses in New England have supported rates of from 1 day-3 acres-80k to 10 days-20acre-100k with decent gains (1+lbs) . I also have two parcels I overgraze habitually while cows are still calving and coyote pressure is on.
My cows cycle through each piece 3 times per season with a minimum rest of 30 days, that being the time that seems to work for me controlling parasites. I did get the cycle down to 21 days one year when we had perfect rainfall and I was very proud of my achievement until it all began to unravel and I had to worm the whole herd.
I think that on a planetary basis mob will be an essential tool to reverse soil degradation and mitigate carbons damaging effect on our environment, but I don’t feel it is as valid a practice where we have ample water and vegetation, this one study seems to confirm my belief.
I was heartened to hear Allan Savory speak to a group of northeast farmers and say he was not here to convert us because we could do everything wrong and still succeed because of our soil and water resources. He said the same was true in the U.K. But that is not the case for 2/3 of the arable land around the globe.
For me RG will remain the backbone of my grazing program and I will dabble in Mob to experiment ( we did one .20,.25,80k last year on an oat cover crop)
This is one study and I assume there will be more. Mob vs. RG is similar to hay vs. stockpiled feed arguments. Time will be the arbiter as the curves of theory and experience either merge or diverge.
A lot of the successful mob grazing systems have rest/recovery for over 100 days many resting a year or more. It gives plenty of time for seed production and plant growth, as well as wildlife and microbial habitat. Also stock density, as Bruce stated, is ‘optimally’ much higher than shown in the research plots. There was no mention of the decreased inflammation in Mob grazed cows, or decreased parasite egg counts as shown in the studies. It also doesn’t mention the better distribution of manure and urine with Mob grazing. This article seemed to pick out some negative stats and dwell on them. Seems quite biased.
Can you point me to the studies you mention?
It’s great to see researcher interest in mob grazing. Bruce Anderson commented about researchers’ findings on the benefits often differing from those reported by many producers. Reasons we have seen for this include the way “mob grazing” is defined. This article characterizes long rest periods as a fundamental aspect of mob grazing. That is not what is taught by the “father of mob grazing,” Ian Mitchell-Innes, who connects with producers around the world on this subject. Ian’s approach to Holistic Planned Grazing was coined “mob grazing” years ago, and focuses on optimizing animal performance by grazing vegetative (adequately rested) pastures, typically at higher stocking densities for a short duration of time. Fundamentals in his approach include avoiding taking more than a third off the plant/pasture (ie. no more than one bite of individual plants), which reduces the recovery time needed before the plant/pasture is ready to be grazed again. Too much rest between grazings negatively impacts animal performance and overall pasture productivity (as the plants become overly mature, growth slows and longer recovery periods become necessary). Too little rest may result in protein imbalances that reduce animal performance, and stress to the plants resulting in the need for longer recovery periods.
As soon as the pasture has recovered it should be grazed, which can be a real challenge at times. Ian talks about buying in livestock to keep up with fast grass growth on his ranch in South Africa. For Northeast U.S. dairies (like ours) with diverse pastures comprised predominantly of cool season perennials it can mean moving cattle very quickly across the farm, with recovery periods of 18 days or less during the spring. Ian also talks about residual, as there will be a good amount of it when pastures are not being overgrazed (as much as 2/3). Higher stocking densities help trample that residue and discourage selective grazing, which also allows for shorter recovery periods.
There is much less species diversity in grazing vegetative growth consistantly.
That has not been our experience, as only grazing a third of the growth and not taking it down short leaves plenty behind that continues growing (we don’t clip the residual) and creates lots of diverse habitat favoring different species of plants, wildlife and soil critters.
For anyone that is really interested in this subject, I recommend carefully reading chapters 22 and 39 of Savory’s Holistic Management. This is a very complex and misunderstood subject and Savory even complained at least as far back as 1999 that researchers were coming to incorrect conclusions about his work.
This is a nice summary of the existing (very scarce) literature.
To quibble a bit: I read the 3 papers from the the Michigan study and it doesn’t seem like a good comparative of Mob-stocking vs lower density rotational grazing.
First, the non-mob system had irrigation, and the mob didn’t.
Second: after only 3-4 years, the rotational system had 18.7 t/ac more Soil Carbon and 1250 lbs/ac more soil nitrogen than the exclosure. This is not possible (>300 lbs N/ac/yr accumulation due to grazing management??!!!) and likely indicates that there were substantial soil differences before the experiment started (the researchers didn’t do baseline sampling.) Comparison to rates of gain from converting to pasture would be misleading, because these research sites were pasture for more than 20 years previously.
If we exclude that study, we are left with the results from Arkansas and Nebraska, which while interesting, are hardly enough to make broad conclusions.
Thanks fro this.
It is interesting that the RG,1,30K seemed to offer the most benefits, which is similar to the system that I use. I sometimes graze a paddock for up to 4 days but not longer. The RG systems are very similar to what Holistic Planned Grazing would lead you towards in a relatively non-brittle environment and echo what Andre Voisin came up with in France 50 years ago with his rational grazing.
What is missing from this research is a comparison of brittle vs non brittle environments and the impacts of this on the environments.
Worth adding that the Ultra High Density stuff often falls down when cow size is too big. Nutrition is stretched in these systems and cows with lower maintenance requirements are needed or condition then fertility then profits suffer. All these variables make this sort of presented research a bit like licking your finger and sticking it in the air to find out which way the market prices will blow….
What is a ‘mob’? If you use the definition of 100,000+ lbs/acre, then one 1,200 lb cow in a pen measuring 10′ x 50′ is a mob that is equal to 87 of those 1,200 lb cows on one acre.
As research scientists, we have not yet developed the ability to mimic the social behavior of large groups of animals when using small herds. We also place multiple test herds in adjacent or near adjacent paddocks where they interact with each other.
I have observed ‘mob’ research using small groups of animals and also have tried to use ‘mob’ grazing myself with 60-70 animals. The animal behavior and impact of these small groups is very different compared to producers using 200+ animals in a group.
I believe this difference in scale is a major reason our research has found less benefit from using ‘mob’ grazing then many producers report. When using small groups of animals as we do in most research trials, we are really just doing a more intensified version of strip grazing rather than true ‘mob’ grazing.
While I also think some producer reports are unrealistic in their claims of ‘mob’ grazing benefits, research reports that suggest little or no benefits, or even negative results, also overlook some of the methodology limitations.
What a great article. The mob grazing proponents always speak in generic terms so it’s good to read some real science. I knew the trampled forage instantly turning into organic matter was a bunch of hog wash, but it’s nice to see real data.
Thanks you for making this careful research available to us. Two comments:
Re: “Their observation was that this was likely the result of having long (300 feet) and narrow (12 feet) rectangular paddocks where animals were stocked so densely they had to regularly move around other cattle to find enough forage.” Perhaps exercise is a good thing. I suspect that small-paddock grazing (like I do) is not the healthiest for the cows. People need exercise; dogs need a run every day. What about cows? One rancher I admire greatly thinks that–unless weather is extreme–his cows might well need a half-mile walk to water each day to maintain health.
Re: “After all is said and done, no farm production system is “sustainable if it is not profitable.” Who would want to work and go broke, obviously. But the statement itself is not as clear as it may be. If producing food is an “essential service,” like maintaining fresh air, water, or providing medical care, or education, . . . is profit necessary in all those other places in order for them to be sustainable. (I’m not trying to be a smart-ass here, but I live in a world where many, many community organizations flourish as non-profits and are “sustainable.”
Thanks again for articles that keep us from becoming ideological about one or another good farming practices.
I’ve spoken to dairy farmers who say that milk production goes UP when the cows have to walk a little farther to pasture, and research on dairy cows used for farm work in Germany from the early 20th century showed that a couple hours of moderate work increased milk yields as well.
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