Wednesday, May 29, 2024
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What Makes Grass Grow Back Fastest – Trampling, Clipping or Cow Spit?

Troy started this piece, Kathy Voth added some, and Jim Gerrish shared his observations. And with all that, we’re still not sure we have an answer.


The heifers moved ahead into a fresh break of pasture while I lingered and admired the trample effect that was left behind. The rough residual was a beautiful combination of chomped grass, top-grazed forbs and a twisted bed of tall, old-man grass folded down like a blanket, upon the soil by the hoof action.

It was so perfect, no further action was needed. So I lingered a bit to consider this question: “Does grazed, and or, trampled forage grow back faster than mechanically cut pasture?”

It’s a discussion that’s long in the tooth around these parts and comes up when the pastures get out of hand and we feel compelled to do something about it. It’s also what a group of Sterling College students in Vermont asked me to explain at a workshop I was leading for them: “Why is grazing and trampling better? And why would trampled grass grow back faster than if you simply clipped it with a mower?”

Friends tell me that using this blade to clip makes grass grow back faster and it is definitely better than a serrated blade.

Not surprisingly, I found myself in a B.S. position. Drawing from my experience listening to famous holistic, mob-grazing practitioners, and believing them, I just said it was so, with only anecdotes for real proof. As I looked at their confusion over how a pile of trampled thatch could regrow quicker than a clean-cut grass clump with full sun, I too, started to question the hypothesis. Adding to my confusion – I have just as many grazing friends who swear that a sharp blade of a disc-bine or sicklebar mower helps the grass grow faster. And then there are us “Bush-hoggers” who shred their plants. That couldn’t possibly be contributing to higher growth rates, could it?

No doubt the mechanical side of things can keep a sward more uniform and vegetative while removing competition from undesirable species. In fast growth times this pruning can be an effective tool for increased dry matter. But is it fundamentally better than a grazing animal? Where is the research that says its better?

Do we know the answer? Or should we chalk it up to personal preference?

I consulted the internet for a scientific answer – where I literally found spit on the topic!

Yes! There are researchers who study animals’ magical saliva to see if the PH, thiamine, and dripping rumen bug juice contribute to increased plant growth and tillering rates. So let’s turn it over to Kathy who gathered some of the literature on this.

Click to download a copy of this paper.

Kathy’s Input:

Scientists were inspired to study the effect of saliva on plant growth because it contains thiamine in concentrations strong enough to potentially stimulate growth. Results of their research have been mixed.

A table in a 1974, 2-page Journal of Range Management “Technical Note” by Reardon, Leinweber and Merrill seems to be the source of the idea that saliva can increase growth by 30%. The methods explanation is a bit unclear, but it appears the authors compared the growth of 15 seedlings grazed by either cows, goats and sheep with plants that they clipped to the same grazed height, resulting in this table:

But when they tested growth due to saliva applied to clipped plants, or to thiamine on clipped plants or on the soil, they found no significant changes.

A study of the effect of bison saliva on blue grama showed no benefit from saliva. Likewise, Canadian scientists found cow saliva had no effect on Altai/rough fescue or Idaho fescue. And a 1986 analysis of the research on this topic found that strong evidence was lacking and that strong growth only occurred in growth-chamber conditions.

On the other hand, a more recent study of sheep saliva on Chinese ryegrass found an increase in tillering and changes to carbohydrate storage in the plant. (This paper had a great description of the methods the researchers used including that they gathered sheep saliva by having sheep chew on a sponge, and then squeezing the sponge out into a tube.) A test of goat saliva on Red Bushwillow in Botswana showed that saliva treated shoots grew much more than untreated shoots, but unclipped shoots grew the most.

While this all leaves us up in the air as to the impact of saliva on plants, many of the papers I read came to the same conclusion: The shorter you graze or clip a plant, the more slowly it grows back, even if you give it lots of rest. Grazing or clipping longer always had better results, thus reinforcing a lesson we’ve all been taught over and over.

With no good answer, I wrote to Jim Gerrish who has a lot of experience running studies, reading research papers, and doing good grazing on the ground. Here’s what he had to add to the discussion.

Jim’s Thoughts:

I think the research of recovery rate with trampling and cow spit is very nebulous because there are so many attenuating circumstances that affect how a pasture is going to recover following perturbation. Thus, I have little confidence in the limited research out there.

Here is my own experience:

I consistently see better regrowth following proper grazing compared to following the mower. Because the pasture sward is uneven when we begin grazing, I expect to see an uneven residual. If we leave a proper amount of leaf area on each of the species in the mixture, because the stock took a bite off of everything, we generally see a uniform and rapid recovery.

Following mowing, particularly a close mowing as most mechanical mowers or conditioners leave, the plants most tolerant of close clipping recover while the species requiring taller residuals (more leaf surface) suffer. Thus, we have more limited recovery following mowing.

Regarding cow saliva, because I do believe in co-evolution of grassland and ruminants, I have to believe there is a metabolic relationship. Does cow spit give us 30 to 44% increases in productivity? I am yet to be convinced.

In my experience, I see more rapid recovery on what I describe as a standing residual as opposed to trampled residual. Here’s a picture of what I mean by standing residual.

And here’s what I mean by trampled residual.

I generally see 10-20 day added recovery time to grow a ton of new feed from a trampled residual compared to standing residual. That is on irrigated land.

We are all products of our own experiences.

Troy Again:

About the time we were all thinking about this, I showed a group of farmers a picture of a June clipped pasture versus grazed and trampled on the other side of the break wire. 100% said they liked the look of the clipped pasture better. But by August the trampled sward was producing twice as much dry matter per acre. Why?

If you went by strictly growth rates, the clipped one got a good jump of forage but the trample slowly fed the biology and covered the soil allowing more diversity and soil life action that accumulated more mass as dry weather ensued. I equate this phenomenon to compensatory gain in cattle. Unfortunately this was not proven by science either way, so I too, practice anecdotes.

Back at our farm, a side by side farm-based trial is underway as my dad clipped the heavy grazing residual next to the trampled animal impact paddock.

Troy’s dad, Ed Bishopp clipping pastures to maintain quality going into stockpiling phase


With little rain and now 30 days of recovery, the two paddocks are running neck and neck.

The trampled paddock next to the clipped paddock, 30 days later.

But there is one glaring distinction that should weigh on everyone’s mind before you hook up an expensive piece of iron to manicure a farm. The temperature of the soil surface on the trampled paddock is 20 degrees cooler and when it rains a tenth or we just have a heavy dew, the paddock retains moisture longer.

I feel our farm’s resiliency is the measure of water retention practices like grazing right for the right reasons. I’m not sure if clipping achieves such a solution.

What are your thoughts or contributions? Do you have some scientific literature to add to the mix? Let’s discuss in the comments below!

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Troy Bishopp
Troy Bishopp
Troy Bishopp, aka “The Grass Whisperer” is a seasoned grazier and grasslands advocate who owns, manages and linger-grazes at Bishopp Family Farm in Deansboro, NY with his understanding wife, daughters, grandchildren and parents. Their certified organic custom grazing operation raise dairy heifers, grass-finished beef and backgrounds feeder cattle on 180 acres of owned and leased pastures. Troy also mentors farmers on holistic land management for the Madison County Soil and Water Conservation District and the Upper Susquehanna Coalition as their regional grazing specialist. This award-winning free-lance writer, essayist and photographer maintains a website presence at


  1. I’m behind but wanted to share an opinion. After 37 years of working with NRCS and growing up on our ranch in Texas. I’ve become a believer in the idea of biology. The bacteria etc in saliva, urine, manure etc seem to really matter. Whether it is in bee survival with glyphosate or pasture/range growth. Everytime we work with creation instead of against it then the soils are better, the plants are better and the animals are better. That is also the right order so people don’t try and feed their way out of managment issues. Last thing is that weather has a vote.

  2. Count me as a fan of clipping, not so much for the speed of regrowth but for quality. I try to clip all my Vermont sheep pastures to 4-6” at least once per season, ideally after grazing in July when all the grasses have gone to seed. The only places that get clipped again are thistle and burdock patches, or when pastures are cut for hay. Since we produce our own hay (whether that is profitable is a good question), I have a tractor and disk mower and can clip pretty quickly. Rotary mowers chop up the grass stems for faster decomposition but are much slower. Species diversity and forage quality benefit. Intensive grazing with clipping allows space for more-palatable grass species, clovers, and other grazing-adapted forbs. It also makes the regrowth more accessible for consumption during later grazing rounds, without the patches of new tillers buried in grass clumps. Without clipping, the less-favored reed canary grass and orchardgrass shade out the shorter species and increase. We are a little understocked (~2.5 ac/AU), but that does allow us to graze into December.
    Jim said it well: there are too many variables to make any broad interpretations of research projects or general conclusions. I find clipping a useful tool for certain sward management goals, but it isn’t required and it can be over-used. Clipping short, early, or frequently will not be beneficial.

  3. It’s nice to see folks are reading and contemplating management decisions.
    I’m a simple practitioner with experience and the willingness to question, as my only accreditation in my environment of cool season perennials and 40 plus inches of rain. Those inquisitive young people were confused and I wanted to try and broaden their understanding of this issue. The “plain community dairy graziers” are always clipping (albeit with horse power) and also were wondering about the connections. I’m afraid I have more questions than answers but “clipping or pruning” is still a pasture walk item that we always (sigh) have to spend too much time on debating. This is why I linger and take pictures to try and understand nature’s bounty. Makes for interesting comments and perspectives which is great. Debate on my friends and you’re all right.
    I am grazing them now (after 2 inches of rain). Below is what was omitted from the original article if you care:

    Fast forward to today and the dry weather that forced us into a 55 day recovery period has done a 360 degree anomaly with more rain in August and September than May, June and July. I will be grazing the paddocks around September 25th for the 4th rotation with 32 days rest and they look and measure almost identical. There may be more litter on the trampled side but that’s it.
    Hmm, do I favor the trampling during dry periods only and when there is adequate moisture; clipping could be a good tool. There is one glaring difference: A tractor, mower and operator cost a helleva lot more than just moving fences to deal with the excess forage. Here in the humid Northeast, the idea of trampling versus clipping is still up for debate. The only thing I proved was having different tools to manage towards your holistic goal is beneficial. Now is your time to debate its merits from your own lens, which you apparently are.

  4. When I was a little boy, I asked my older grandfather why his eyebrows were so bushy. He thought about it, then said it was because the cows always liked to kick his face. The dogs, too. I decided right then and there to never allow any animal to lick my face ever again. Guess it didn’t help because half a century later, I need a hedge clipper to keep up with them. Saliva has my vote. *On a serious note*, King Ranch owned land all across the nation. In areas with plentiful rainfall, they grazed, then clipped each pasture in rotation. Then, oil was cheap.

  5. As we have significant rescue, I saw good results clipping after grazing and before seed development resulting in taming the rescue beast. Above normal rains have brought that to a close. Depends on the forage which varies in my rotated fields!

  6. I did find this an interesting article. I do believe saliva is a component of the biology left behind from animals grazing on the landscape. (Not sure on how much it individually impacts things.)

    I wonder about how true to nature the study was carried out. I think one should examine the time involved from when they collected the saliva and applied it. Was it in cold storage at that time? Was it kept at room temperature? Was it left in the back of a pick up truck in a glass jar on a 90 degree day for 3 hours? There are living organisms in that saliva and if it was applied in any way other than immediately after collection I feel the results will be less than what would be observed if an actual animal grazed a plant and its saliva touched the plant. The biology would be altered and skew the results. Talk to anyone about putting inoculant on legume seed or biologic bases crop treatments and they will tell you time and temperature can have a huge impact on results.

  7. Good stuff folks.

    As someone just getting started in this new to me tall grazing world, it’s a bit of relief to know I have one less thing to worry about.

    I think I will set aside worrying about any impact saliva might have on growing grass and, as I learn how to graze our land, continue worrying about the zillion other things there are to worry about. 😉
    Happy trails!

  8. I have a strong belief in staying close to the natural world. I have never seen a tractor or piece of equipment eat, trample, urinate or defecate!

  9. You’re all very interesting and/but out of my league, and/but there’s no mention of WHAT SPECIES are being grazed or mowed. I suspect there’s good reason(s) for this omission, but I can only ask what they may be. In short -huh?

  10. Trample grass to feed microbes that make nutrients available trapping/preserving solar energy, air and water to grow more grass sustainably. See practical farmers of iowa talk on YouTube by Mark Bader for the scientific explanation.
    The cow spit theory may pertain to grass being inoculated to help digestion.
    Mowing an expense that cows pay to do for you.

  11. I really enjoyed this discussion. I have to also question some how much the ruminant “drool” might impact forage growth, but do think that the synergistic interaction between plants and animals could be advantageous to plants. I believe that I’ve read that cows produce more than 200 liters of saliva in a single day to buffer fermentation in the rumen…that’s a lot of potential drool or spit! I’m sure that “some” saliva is left behind during the grazing process. Another thought might be the deposit of minute amounts of biota from the fermentation process of the rumen that also could be somehow beneficial to the plant. On the other side of it. I see more mowing done for aesthetics than for any economic or biological reason. In fact, mowing sometimes probably destroys more good forage than improving it.

  12. Standing residual grass will regrow faster than trampled grass, because it regrows from the standing stems and leaves remaining, whereas the trampled grass has to send up a shoot from the roots to regrow. If we are managing residual properly, we are leaving significantly more leaf and stem than if we cut the grass, so that should help improve regrowth–although modern varieties of alfalfa can regrow pretty quickly after being cut, albeit with lots of input cost.

    That doesn’t mean that it’s always better to graze so that you leave standing residual, because I believe that my pastures benefit from the trampled grass, especially during hot, dry summers, in which the trampled grass acts like a mulch keeping the soil cool and moist. Besides, the way I manage grazing on my heavy clay soils, which are too wet to hay is to allow them to stockpile forage in May/June, which serves as pasture well into July. The taller it becomes the more is trampled, as I allow the cattle to have more selection to keep gains high.

    By the way, don’t let anyone put “science” into some sort of lock box for which you need a PhD to unlock. Science is better thought of as a toolbox that is open for us all to use. The tools are a set of methods that help us make observations without, hopefully, fooling ourselves. The statistical analysis that is done on those results is meant to provide a level of confidence in our results. We can use scientific methods on our farms/ranches to answer questions, which in many cases create more questions. There are good on-farm research tools and grants available through SARE, or if you are in Iowa, through Practical Farmers of Iowa.

  13. I would be quite surprised to find that livestock spit had any real effect on regrowth due to the very tiny amount left in the pasture. Consider how cattle eat tall lush grass: they wrap their tongue around it, rip it off, then pull it into their mouth. The don’t lick the residual grass. Sheep nibble grass leaves off using their teeth. Unless livestock are drooling rather impressively, shouldn’t be much quantity or impact.

  14. At the risk of being obsessive and boring, please allow me to wave the flag of economics. While the question of grazing vs trampling vs mowing is fascinating from a scientific standpoint (and I really like science), readers should keep in mind that any perceived or actual benefit from mowing must be tempered by the fact that the humans involved have to own a tractor and a mower and the fuel and parts to complete the task. Oh, and most importantly, they also have to “own” the time spent driving around in circles. Conclusion: mowing would have to produce fantastically more grass to be a reasonable practice.

  15. One of the challenges I have is the landowner of the large farm I lease likes to get on his mower and clip a field after all rotations are done in that field to control the thistles. Thistles are one thing I’ve had trouble getting the cows to trample sufficiently. Because the landowner waits until all rotations are done in that field and all polywire is removed, that means he’s usually clipping some of the regrowth as well. I’d really like to find some data that shows just how much forage is being lost by setting the growth back in this critical early stage.

  16. Thank you for this article-articles like this are what makes OnPasture unique and thought provoking. It’s nice to have three smarter than me people roll around a question that, like an earworm, rolls around in my head far too often without a concrete answer. And an added bonus, Jim Gerrish throws in words like perturbation that send me to the dictionary to learn my new word of the day!

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