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Putting science into grass management

The Grazing Response Index scores foliage removal, grazing period and recovery time

When it came out of Colorado in the 1990s, the Grazing Response Index (GRI) was strictly at home on the range. Now Ducks Unlimited Canada’s Jodie Horvath says that, with a few tweaks, the grass management tool can help graziers on Western Canada’s tame pastures, too.

“When you’re a farmer, a lot of things feel out of your control, especially with the weather,” says Horvath, a DUC conservation programs specialist and Saskatchewan grain and cattle producer. The GRI “helps you realize there are things you can control, including the number of animals you put out, where they go, and how long they’re out there — so you do have some decision-making available to you.”

With the backing of the Saskatchewan Forage Council and Agriculture and Agri-Food Canada, Horvath tested the index during three years of grazing at DUC’s Touchwood Hills Conservation Ranch north of Fort Qu’Appelle. “There aren’t a lot of ways to measure and grade how we’re doing on our tame pastures,” she says. “I thought the GRI would be something really practical that we could implement easily on a farm for the average producer.”

Putting grass first

The GRI focuses on three aspects of grazing and pasture growth: grazing intensity — the amount of leaf area that is bitten off by grazing animals; the frequency — how often leaves are bitten off as the plants try to regrow; and the plant’s opportunity to regrow — the rest and recovery pastures get after grazing.

GRI grades “how the grazing pattern in a particular year affects the health of the plant,” says Mae Elsinger, Brandon-based range management biologist with Agriculture and Agri-Food Canada. “It’s about damage to the plant, recovery from damage, and the overall health by the end of the year.”

Plants are like solar power systems, she adds — the more leaf area bitten off, the less solar energy the plant captures. When growing leaves are repeatedly chomped, stressed plants are forced to draw stored energy from their roots, like an underpowered solar system draining its storage batteries. As the grass weakens, it’s shaded out by less palatable or weedy species. The result is a less productive pasture.

The GRI focuses on three factors: grazing intensity, frequency and the plant’s opportunity to regrow.
photo: Supplied

Horvath’s major challenge was adapting a system designed for native range grasses into one that works for cool-season domesticated species. When the GRI was brought into Canada, researchers at British Columbia’s Thompson Rivers University tested the approach on common range grasses, including bluebunch wheatgrass, rough fescue, and pinegrass to ensure what works in Colorado is applicable north of the 49th parallel.

Elsinger says the same detailed lab work hasn’t been done on tame species, including the alfalfa, meadow and smooth bromes featured in Horvath’s test pastures. But she adds experienced managers know tame pastures behave differently from native range.

“Tame forages have evolved under a totally different system,” Elsinger says. While Prairie grasses were occasionally trampled, grazed, or burned — sometimes severely — they probably had extended rest periods. Tame species developed in Europe and Asia under thousands of years of regular and repeated grazing, so “these grasses have just adapted to higher-intensity grazing than native grasses.”

The new tame version of the GRI reflects this. When it comes to grazing intensity, the tame GRI defines “light” grazing as taking up to 60 per cent of the stand, compared to just 40 per cent for range. Ditto for “opportunity for regrowth,” where a six-week rest for a tame pasture is equivalent to a range receiving a “full season” of rest after grazing.

Finally, there’s the frequency of grazing. The range GRI awards top marks for a once-over rotational grazing system, but in most of the West, “the way we manage our tame pastures is often different than the way we manage our range pastures,” says the Saskatchewan Forage Council’s Laura Holmyr, who ranches near the U.S. border. “A lot of times we have two or maybe three times over” for tame pastures.

To allow multiple passes on tame pastures but prevent tame plants from being bitten too many times in any one pass, the updated GRI tracks the longest period livestock graze a single paddock. Assuming it takes seven to 10 days for a plant to regrow to the state where it can be grazed again (a timeline adopted from the original GRI), graziers earn a positive score for restricting a grazing session to seven to 10 days in any one pasture. Leaving the beasts in for more than 21-30 days, on the other hand, draws a negative score.

Holmyr adds managers may want to tweak this seven- to 10-day rule to fit their own knowledge of local plant growth. “Personally, at my place, we would never leave our cows on tame pasture for seven days, unless it’s August and nothing is growing. We always move them in four days or less.”

Graziers using the index need to note the in and out dates for each pasture, and track how much of the stand is being grazed on each pass. When estimating grazing intensity, it’s best to compare with an ungrazed stand nearby. Areas near ditches, fence­rows and neighbouring fields may be an option, but Horvath used grazing exclusion cages borrowed from AAFC. Pegged to the ground with bent rebar, the cages are strong enough to shield the grass inside, even while cattle scratch themselves on the cage.

By comparing what’s in the cage to an “average” grazed area five metres away, “it’s a great comparison as to what they’re actually removing, and that was an eye-opener for me,” says Horvath. “Honestly, you think the animals have removed only about half, or there’s lots of grazing out there yet. But when you have those grazing cages they really provide an important visual.”

Filling out the scorecard

After that, it’s a matter of working out the annual scorecard for each pasture. For example:

  • Have the plants in Field A been grazed at less than 60 per cent of their foliage? Score one.
  • Were cattle on the field for less than seven days during their longest grazing period? Score another one.
  • Did the field get six weeks of recovery time between grazings? Score two.
  • Add up the total, and congratulations, Field A has maxed out at the highest possible score, four.

But say Field B got different treatment. It was intensively grazed (with cattle removing more than 85 per cent of the foliage) for a score of minus one. The cattle also spent at least a month in the field on their longest grazing session, so that earns another minus one. And though the field got a month between grazings, giving it “some chance” in the opportunity for regrowth score, that still only merits a zero.

At the end of the year, Field A has earned a four, while B is suffering with a minus two. If this treatment continues, B will eventually become rundown. Options include giving B a little more TLC, and increasing the pressure on A, or subdividing pastures to get a better handle on grazing intensity by reducing time on any one paddock and boosting rest periods.

GRI “works especially great in a rotational system where you have the flexibility to make adjustments,” Elsinger says. “If you have one big pasture and your animals are grazing season long from May to October and you get GRI results you don’t like, you’re not going to have much flexibility to change, unless you adopt cross-fencing.”

The GRI “gives you a starting point for how to improve things, and an indication of the trend over time,” Laura Holmyr says. “Have I been degrading this resource? Have I been improving it? What can I maybe change to do some more regenerative-type grazing instead of taking, taking all the time?”

At the very least, Jodie Horvath adds, the GRI is a simple way to inject more science into the art of pasture management. Sometimes, she adds, better management “is the one piece of control you have, when things feel out of control.”

To learn more about the GRI for tame forages, visit the Saskatchewan Forage Council’s website.

This article originally appeared in the 2018 Forage & Grassland Guide.

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