Calculating the Graze Period

Calculating the plan

Step 9  - Rate paddock productivity

Step 10  - Determine the length of recovery periods

Step 11 - Calculate grazing periods for each paddock

Step 12 - Not applicable to an Open plan

Step 13 - Not applicable to an Open plan

Step 9 - Rate Paddock Productivity

Not all paddocks deliver equal ‘per hectare’ (‘per acre’) performance.  For example, if there were two paddocks of equal size on a property, and one was known to yield twice the forage as the other, then sensibly, a given number of animals would graze the better paddock for twice as long as they would graze the lesser paddock.  The purpose of this step is to take into account what you know about the relative productivity and feed quality of your paddocks (and you can be sure you do know a lot about them).  

Two ways to rate a paddock

1.  Using a ‘1 to 10 rating’ basis

In the first year of planning you will probably use a 'best guess' rating, and I recommend using a ‘1 to 10’ scale.  For each paddock in the grazing cell you are planning, assess its productivity against the others.  Allocate the highest rating, 10, to the paddock you consider to be the most productive, then rate the others against it.

This is without doubt a subjective step, so look at each paddock and make a judgement based on your knowledge about its productivity and quality of feed produced.  

NOTE: Within any group of paddocks you do not have to rate one as 10 and another as 1.  If you rate the best paddock as 10, and you feel the remaining paddocks are all 80% as good as it, there is nothing to stop the remainder being rated 8!   You do not have to be precisely ‘right’, as all you want to do is resolve glaring disparities between paddocks.
 

NOTE 2: At this stage you are only looking at performance per hectare or per acre.  Shortly you will factor in paddock size as well.  

NOTE 3: Make sure each paddock is assessed only against the group of paddocks making up this cell.  It is conceivable that a paddock that you rated as 10 in one group of paddocks might be given a lower rating if it were included in and one of an entirely different group of paddocks.

2.  Using ADH data from the just completed Closed plan
If you have just completed a closed plan you should use the data from Column 8 of that plan (Total Yield - ADH or ADA) as the rating for this plan.  This provides accurate ‘real-time’ information that picks up changes in paddock performance as a result of your management.

Entering the data

Using either basis, do this:

  • For each paddock in the cell for this season, enter into Column 1 (“Actual/Estimate”) the Paddock Rating you have chosen (either the 1 to 10 rating, or the actual ADH (ADA) that you take from Column 8 of your recent Closed Plan
  • In Column 2, enter the 'Estimated Relative Paddock Quality'.  Calculate this by multiplying the Rating you just placed into Column 1 by the Size of the paddock you previously placed in Column 3 (hectares or acres).  For “Jacks” paddock in this example, multiply 6 x 88 = 528.


Then:

  • Add up all the 'Estimated Relative Paddock Quality figures in Column 2, and divide the total by the number of paddocks available in the cell.
  • Place this answer—which is the 'Average Paddock Rating'—at the foot of Column 2.



Note: If there is a change between months in the “Number of paddocks available” as shown in Row 26 (Step 7), you must recalculate the Average Paddock Rating, removing from the calculation any paddock(s) Excluded at any time, and including any paddocks that are added in.  If you end up with three different “number of paddocks available”, you must calculate the three different “Average Paddock Ratings” and place the three figures at the foot of Column 2.

You now have the basis for comparing paddocks to each other.  In our emerging example, an ‘Average paddock’ has a Relative Paddock Quality of 317.2.  All paddocks with a Relative Paddock Quality greater than 317.2 will be grazed for proportionally longer than an average paddock, and all paddocks with a Relative Paddock Quality less than 317.2 will be grazed for proportionally less time than an average paddock.  Shortly we will work out how much more (or less) this will be.


When you are using the Excel model to assist your calculations


In Section B of the Worksheet enter the rating (1 to 10, or from Column 8 of the recent Closed plan) for each paddock, as shown below.  The worksheet automatically calculates the Relative Paddock Quality for each paddock, and adjusts the Average Paddock Quality, which is recorded in Cell D23 of the worksheet.
 




Step 10 - Determine the Length of Recovery Periods

During the period the plan will operate, it is likely that plant growth rates will at times be very rapid, and plant recovery will also be rapid.  It is also almost certain that at times the prevailing seasonal conditions will mean plants are recovering but very slowly.  The graph below shows the possible extremes, and clearly shows that using a constant recovery period is a major trap.  

Over the years farmers who have adopted constant recovery periods have progressively experienced loss of plant vigour and productivity, and in many cases their entire property!




Audio Clip

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During this step, you need to make an estimation of two times that are applicable for your local conditions:

  1. Under FAST growth conditions, the likely number of days for full post-grazing recovery that might be required by the slowest recovering species present in your pastures
  2. Under SLOW growth conditions, the likely number of days for complete post-grazing recovery that might be required by the slowest recovering species present in your pastures
For our example let's assume that experience suggests that in periods of extremely rapid growth all species will be fully recovered in 50 days, and that in very slow—but nevertheless active growth—the slowest recovering species might take as long as 150 days to recover.
  

Write the answer, in days, for every month of the plan, in Row 27. expressed as Fast/Slow  eg 50/150.



When you are using the Excel model to assist your calculations

Enter the Fast Recovery period in the yellow coded Cell E28, and the Slow Recovery period in Cell F28.  The worksheet will automatically calculate the grazing periods for each paddock.


If you use the Excel model, you can pass over Step 11, below, as the calculations are complete.  Print out the spreadsheet and transfer the information to Column 4 of your Grazing Planning and Control Sheet.





Step 11 - Calculating grazing period

Now we are getting to the meat of the deal.  There are two steps in calculating the ‘Grazing Periods’ for each paddock.  First, the Average Graze Period must be calculated.  That is the period a paddock that is an average ‘Estimated Relative Paddock Quality’ would be grazed for.  

The second step is to calculate the Actual Graze Periods for each paddock, under Fast and Slow growth conditions.

A. Calculate Average Grazing Periods (AGP)
Average Grazing Periods are a function of, and are effected by three things:
  1. Recovery Period required by the plants
  2. Number of Paddocks in the Cell
  3. Number of Mobs passing through the Paddocks in the Cell. 
The number of mobs is important to consider, because a paddock that is occupied is not recovering—that is why it must be taken out of the calculation. If you are using Leader/Follower, then two occupied paddocks must be considered.  See this video for more information.

Video Clip

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At Step 10 you have already identified the two extremes for rate of recovery, in our example FAST = 50 days and SLOW = 150 days.  At Step 4 it was noted, in Row 25 that there would be a single mob of animals  (comprising 1,500 ewes due to commence lambing on September 15).  We now have the data required to calculate AGP.

To do this, let’s quickly look at the basic formula, which looks like this:



For our example:
Calculating AGP for FAST growth conditions



Calculating AGP for SLOW growth conditions



For each month, write your answer in Row 28.



Variation in paddocks available: If at Step 7 it was decided that the number of paddocks available would vary between months, then Average Graze Periods for both ‘Fast’ and ‘Slow’ growth must be calculated for each different number of paddocks.

Decimal points: If the answer contains decimal fractions, you must include the decimal.  Do not 'round’ this number, because may throw your results out and quite seriously effect your animal performance and pasture productivity.

For further information: More complex grazing plans require additional calculations. Please read P102 of the Holistic Management Handbook, or call us.


B. Calculate Actual Graze Periods for each paddock
The Actual Grazing Period for each paddock can now be calculated.  This is a function of:
  • The Relative Estimated Paddock Quality for the paddock, shown in Column 2 (Step 9),
  • The Average Quality of all the paddocks in the cell, found at the foot of Column 2, and
  • The Average Graze Period(s) you calculated above.
The basic formula for each paddock is:



We will use our emerging example to demonstrate the process.  For each paddock there are two figures to be calculated:

The Actual Graze Period under FAST growth (eg 50 days for recovery
The Actual Graze Period under SLOW growth (eg 150 days for recovery.

Example using “Jacks” paddock
a. Under ‘Fast” growth conditions



This means that when plants are recovering rapidly, Jacks paddock is to be grazed for 6 days.

b. Under ‘Slow” growth conditions



This means that when plants are recovering slowly, Jacks paddock is to be grazed for 18 days.

Place the answer for each paddock goes into Column 4 as 6/18.
(Column 4 is to the right of the Grazing Plan and Control Chart, as shown below)




Why this make sense!
‘Jacks’ paddock has a Relative Paddock Quality of 528, which is 66% greater than the Average Relative Paddock Quality of 317.2 (found at the foot of Column 2).  Therefore it stands to reason that Jacks should be grazed for 66% longer than an “Average” paddock.  Let’s check, using the ‘Fast’ recovery data: 5.94 days/3.57 days = 1.66 or a graze 66% greater than the Average Graze Period under Fast conditions.  It works!

Conversely, paddocks that have a Relative Paddock Quality less than the Average Relative Paddock Quality will be grazed proportionally less than the Average Graze Period.


Variations in paddock numbers

If, in Row 26 you have variations in paddock numbers from month to month, then for each different paddock count you must calculate a new set of Fast/Slow graze periods.   You may wish to use the blank column to the right of column 4 to hold the additional set or sets of Actual Graze Period figures that you calculate.


CHECK FOR OVERGRAZING RISK in paddocks with the largest calculated grazing period.

This step is important in avoiding a potential problem, especially when plant growth rates are “Fast”. It is also a good way to check that your maths are correct.  There are two parts to the process:

Check your maths

  1. Add up all the left side figures in Column 4. The answer should match the sum of:
Planned 'Recovery Period’ plus the ‘Average Graze Period’.

  2. In our example, the total of Column 4 for the Fast recovery period should be 50 + 3.57 days = 53.57 days.  It is correct, as the image below shows (it adds up to 53.6 days).

This means, in this example, that it will take 53.6 days to pass through every paddock once.



Check for risk of Overgrazing

Find the paddock with the longest graze period under Fast recovery conditions.  In this example it is Town paddock, at 8.3 days.  

For Town paddock the actual recovery period will be 53.6 - 8.3 days = 45.3 days.  ie Town paddock will not experience the complete recovery you required it to have, which is 50 days.  It is deficient by 4.7 days.
 
This is a problem because, under Fast growth conditions much of the recovery occurs in the last few days—it is the power of the sigmoid curve!

Solution: There are two easy alternatives:

  • You could plan to stay in one or more of the other paddocks in the cell for a little longer - say half a day in each of 9 paddocks. The purpose is to ensure that the cumulative cycle time is extended by the deficiency of the longest grazed paddock.  If this deficiency is corrected, all other paddocks with an excessive grazing period are automatically adjusted.  The possible effect is a minor impact on animal performance which will be more than offset by maintaining proper plant health.
  • You could temporarily subdivide Town paddock with electric fencing.  This one action could address the problem, but requires human effort and should be tested towards your holisticgoal.
The grazing period of a paddock viewed another way

Whilst a paddock is being grazed, apart from supplying forage to the animals, it is important to recognise that the paddock is simultaneously delivering its contribution to the recovery time of every other paddock in the grazing cell.



STEPS 12 and 13 do NOT apply to an OPEN PLAN

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