GRI Calculator Instructions

Instructions for Completing a Grazing Response Index Assessment

  • Frequency Index

To estimate the number of times the plants could be grazed, divide the number of grazing days during the growing season by the 7- or 10-day regrowth period. Use local knowledge of plant growth rate as affected by time of year and weather conditions to determine whether to use 7- or 10-day regrowth period on your calculation. If the pasture was grazed for more than one grazing period during the growing season, select the longest grazing period only to score using this index.

  • Intensity Index

Intensity is measured at the end of the grazing period and is described using three levels of defoliation: light, moderate and heavy. Grazing exclusion cages are placed in representative areas to provide a visual reference to determine the percentage of the foliage that was removed during grazing. Estimate the percentage of leaf material removed from the plants and assign the corresponding score.

  • Opportunity Index

Opportunity for regrowth is assessed at the end of the growing season based on two factors: the apparent level of recovery of the vegetation and the knowledge of whether the plants had a full opportunity for growth before grazing. A six-week period for regrowth would be considered a full season of regrowth and receive a score of 2 under average conditions on tame pasture. It should be noted that this is a somewhat subjective measurement. The important point to remember when scoring is that it is not just a measure of time, but also quality of rest period. Time of year grazed, the amount of precipitation received, insect infestations, early killing frosts, a late start to the growing season and any other factors that impact potential for regrowth must be considered in scoring for this index factor.