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GRI gets the green light for tame pastures

Forage: News Roundup from the June 2017 issue of Canadian Cattlemen

Putting numbers to three observations that form the Grazing Response Index (GRI) will give you a good idea as to whether your management practices will benefit, harm or have no effect on plant health in the long run.

If the scores for grazing intensity, grazing frequency, and opportunity for regrowth during the growing season on a pasture add up to a negative overall GRI score, then you’ll know right away that small problems could become big problems over time if you continue with the same practices on that pasture.

Individual scores for each of the three observations will tip you off as to adjustments that could be made to better the score next year. Scores from year to year will indicate whether you are on the right track.

The GRI was developed at Colorado State University and is widely used south of the border as a simple way to evaluate grazing effects on native grasslands between full rangeland health assessments every five years or so.

Agrologists with Thompson Rivers University in British Columbia and Agriculture and Agri-Food Canada in Saskatchewan and Manitoba found that the GRI method proved out on native pastures here (Canadian Cattlemen, July 2015).

The unanswered question was whether the GRI would be useful for monitoring tame pastures because growth habits of tame species and their responses to grazing differ from those of native forages.

Findings from a three-year project putting GRI into practice on three tame pastures in the black soil zone of east-central Saskatchewan say yes, but with minor modifications to scoring.

According to the Saskatchewan Forage Council’s report on the project, the grazing intensity index has been adjusted to account for the fact that tame forages usually tolerate heavier grazing than native forages.

Grazing cages to block cattle from grazing representative areas within a pasture help with estimating the percentage of forage grazed off during each grazing period there.

Scoring grazing frequency is the same for tame and native pastures. The difference is that only the longest grazing period in a tame pasture is scored even if the cattle graze there multiple times over the season.

Grazing frequency is an estimation of the number of chances cattle would have had to graze the same plants more than once during a single stay in a pasture. Plants will grow tall enough within seven to 10 days to be bitten off a second time, so take the number of days cattle were in the pasture and divide by seven or 10 to estimate how many times the plants may have been bitten.

Research has already established that one defoliation will benefit plants, two will have little effect, but three or more during a single stay in a pasture will have negative consequences for long-term plant health.

Scoring the opportunity for regrowth on each pasture at the end of the growing season is the same for tame as for native forages. The difference here is that six weeks of rest is deemed to provide a full season of regrowth for tame pastures.

The six weeks is under average growing conditions, so think about how factors such as the mix of forage species, time of grazing, amount of precipitation, insect pressure or frosts may have reduced the potential for full regrowth during the six weeks.

In conclusion, the authors suggest the GRI method allows for a simple way to focus on one or more aspects of grazing management that may be negatively impacting pastures. For example, if a negative score is generated based on the frequency value, this can be improved by using temporary fencing to ensure that cattle are moved more frequently. If all pastures are generating negative scores for the intensity factor, this may indicate the farm is overstocked and herd numbers should be reduced or that additional grass or alternative feed sources be provided.

They also found the GRI to be user-friendly as it doesn’t require much technical expertise, time or money. Grazing cages and photos are useful, but simply marking the calendar to show the days in and out of each pasture would give enough information to get started.

The full report with sample worksheets for tame and native pastures is on the SFC website, www.saskforage.ca.

AAFC’s report on the original evaluation of GRI for monitoring native pastures can be found as a PDF at this URL: publications.gc.ca/collections/collection_2014/aac-aafc/A59-22-2014-eng.pdf.

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