Pasture assessments

Improving pasture use with regular assessment

You can only manage what you measure. Regular pasture assessment such as a weekly or fortnightly farm walk is important for pasture utilisation. A pasture assessment will help answer the following:

• How much pasture have I got today?
• How much will I have next week?
• How big is the surplus or deficit?
• How much pasture remained when the cows left the paddock?

Assessing your farm's pasture regularly, using tools like feed wedges, spring rotation planners, or autumn planners depending on the season, gives you important information to make feeding decisions.

Having accurate and timely information about your pastures helps you align the available pasture with what your herd needs. It also helps you identify if you have too much or too little pasture. Properly allocating pasture is crucial during the peak growing season to reach desired leftover amounts and avoid long-term consequences throughout the season.

Pasture measurement

There are several ways that pastures can be assessed and measured. Some of the common methods are calibrated eye assessment and manual measurement using the Rising Plate Meter (RPM) or an electronic meter or probe. Another approach is a sensor attached to a quad or ATV bike such as the C-Dax Pasture Meter (also known as the Rapid Pasture Meter).

The Rising Plate Meter and C-Dax Pasture Meter

This approximates pasture mass and puts hard numbers on the grazing management plan. They are designed to measure ryegrass and clover pastures and provide a point of reference when several people are making pasture decisions.

Calibrated eye or visual pasture assessment

This can be as good as any current tool, but requires practice and calibration. Calibration can be achieved through DairyNZ discussion groups, regular farm walks with a farm consultant or the farm team, or through occasional comparison with a tool like the RPM.

Pasture condition score tool

The pasture condition score tool is a visual assessment guide which provides an alternative way to compare paddocks for renewal or maintenance such as fertiliser, under or oversowing. Many pastures have less than desired density of ryegrass and clover because of treading damage in winter, or insect and drought during the previous summers.

Assessing the damage in each paddock by ranking them one to five based on visual scores, can help establish a plan for each paddock.

See the Pasture condition score tool.

Recording and decision support

Regular pasture assessment, which is well recorded (notebook, spreadsheet or in a suitable computer program) can provide valuable information not only for short term decision making but also for future management decisions.

Regular pasture data can provide:

• Annual farm growth rates
• Individual paddock growth rates
• Seasonal average pasture cover targets.

This information can be used to build a feed wedge, increase accuracy in feed budgeting and to assess paddocks for renewal or development.

The feed wedge and the Spring Rotation Planner are the most important tools for pasture management

• Use the Spring Rotation Planner from calving to balance date
• Use the feed wedge after balance date through to autumn.

There are a range of computer programs and software available through commercial suppliers aimed at helping make decisions from pasture data.

View programs and suppliers here:

All programs offer a feed wedge and some products provide additional reporting tools.  Examples of other functionality that may be included is below.

Over 12 months most paddocks will have 9 to 10 grazings. It only takes one poor grazing event to adversely impact the next 2 or 3 grazing events.

Pasture allocation affects the quality and quantity of pasture at future grazings. The purpose of allocating pasture accurately is to optimise both pasture eaten per ha and animal performance.  This requires having targets pre and post-grazing, measuring regularly, and planning the grazing event.

Effective grazing management

Managing grazing yield and leaf stage will enable the correct decisions around grazing order, ensure the right targets are chosen, and pre-grazing and post-grazing targets are achieved.

• Understand your target covers to set the correct rotation length. Rotation length should be set based on the assessment of leaf stage for your farm (See Leaf stage for more information on setting rotation length) while ensuring the paddocks are grazed within the desired pre-grazing range.
• Monitor cow intake and residuals. Accurate pasture allocation is driven by pasture assessment (e.g. weekly farm walks). Skip paddocks when required.
• Consider the management of leaf stage. Nitrogen fertiliser boosted ryegrass pastures will have higher yields (N boosts leaf size) at lower leaf stages, potentially requiring grazing before the 2 ½ leaf stage. Consider the farm’s feed demand compared to the amount of pasture grown. A more advance leaf stage (longer grazing interval) may be more favourable on higher stocked farms.
• Changes to pre-grazing yields and adverse weather events will make achieving residuals challenging. In prolonged periods of high rainfall, target residuals may not be attainable, however it makes good sense to correct these residuals when possible (lower pre-grazing yield in next rotation, remove for silage, top).

High grazing intake

To achieve intakes of 16-18 kg DM/cow/day pre-grazing yield must be managed at between 2800-3200 kg DM/ha to maintain high quality pasture in front of the cows and make it easier for the cows to reach a 1500 -1600 kgDM/ha (3.5 - 4cm) grazing residuals.

Low grazing intake

Where lower dry matter intake (DMI) is sufficient (14 kg DMI), such as in late lactation, pre-grazing yields up to 3800 kg DM/ha may be grazed to a 1500-1600kg DM grazing residuals.

Calculating pre-grazing cover

Achieving post grazing residuals and good animal performance requires accurate pasture allocation. This allows you to calculate pre-grazing cover. (Stocking rate x pasture intake x rotation length) + optimum residual = pre-grazing cover.

Achieving post-grazing residuals and good animal performance requires:

• Accurate pasture allocation
• Calculating pre-grazing cover, and evaluating cow intake and rotation length.
• Use of corrective action when targets are not met.

Grazing residuals

• Grazing residuals are the key indicator of pasture utilisation following grazing. Poor pasture utilisation results in high post-grazing residuals, i.e. pasture wastage.
• High post-grazing residuals will suppress average pasture growth rates and will reduce pasture digestibility at the next grazing, impacting animal performance.
• In late spring, perennial ryegrass tiller moves from vegetative to reproductive growth. This leads to stem elongation, increasing the amount of stem in the pasture being eaten. This may lead to slight increases in post-grazing residual height if not managed well. If this continues then when feed becomes short (e.g. in summer), cows will be forced to eat lower quality stem.
• Achieving target residuals in spring will reduce reproductive tillers minimising the increase in grazing residual that would otherwise occur.
• Winter offers an opportunity to reset the residual level for the coming season and ensure leaf growth is promoted at the base of the pasture.

Consistent even-grazing height

For a ryegrass clover pasture a consistent, even grazing height (few or no clumps) will be 7-8 clicks on the rising plate meter, 3.5 to 4 cm compressed height or 1500 - 1600 kg DM per ha in spring.

The plate meter will over estimate residuals where there are weeds or there is pugging damage. Grazing residuals

Calculating Pasture Growth Rates

It is important to have pasture growth information for your farm for strategic planning (e.g. annual feed budgeting, identify underperforming paddocks) but also for tactical management (e.g. predicting a surplus situation)

Pasture growth is measured in kg DM/ha/day. Working out the growth rates for your farm requires good record keeping. In most cases, software available for feed wedges and pasture data can calculate growth rates at a farm level.  The method below will allow you to calculate pasture growth rates at a paddock level.

How to work out growth rates

• Measure grazing residuals for each paddock e.g. 1,500kg DM/ha
• Measure again before grazing e.g. 2,800 kg DM à 1,300 kg DM pasture grown since last grazing
• Divide this by the number of days between measurements e.g. 24 days
• The average growth rate is 54 kg DM/ha/day

What you need: a board or spreadsheet to record each grazing date for each paddock and to record the corresponding pre-grazing and post-grazing cover.

This information can then be used as a guide for the next grazing round (and following seasons). Saving this information will allow you to build up a file of data that can be used for feed budgeting purposes.

Average Pasture Cover (APC)

Average Pasture Cover is the measure of the quantity of pasture on the farm. Having APC targets for the farm at key times of the year is important for managing pasture supply and demand.

Understanding APC

APC is a key indicator of feed on hand and is the most reliable way of feed budgeting in the short-term. The amount of pasture on hand can be estimated enabling short-term tactical decisions to be made with relative confidence.

• Average Pasture Cover (APC) is an estimate of pasture quantity on the farm.
• Maintaining APC above 1800kg DM/ha in early spring and between 2000-2400kg DM/ha throughout the season will help maximise growth rates.
• When average pasture cover is low (and the rotation length is not slowed) this may result in pastures being grazed before the 2 leaf stage. Grazing at (or before) the 2-leaf stage reduces growth rates and compromises total pasture DM production.
• By observing changes in pasture cover on a week-by-week basis, the grazing manager is in a good position to respond to changes in APC before they become critical.

Average Pasture Cover and Pasture Growth Rates in Spring

How to calculate APC

The APC is measured in kg DM/ha and is determined by calculating the cover on each paddock, multiplying the area of each paddock, adding all these together and then dividing by the total area.

1. Estimate pre-grazing cover on each paddock including the one just grazed (grazing residuals figure)
2. When all paddocks have been assessed, multiply the area (ha) by pre-grazing cover (kg DM/ha), for each paddock
3. Sum all these together, and divide by total area

Example:

APC is found by dividing the ‘pasture cover x area’ by the ‘total area’.

(APC:  17,250 kg DM ÷ 8.5ha = 2,030 kg DM/ha)

Rapidly estimating average pasture cover: If you have a large number of paddocks, estimating the average pasture cover can take several hours. It can be estimated roughly by taking the average of the five longest paddocks (with the most feed) and the five shortest paddocks (with the least feed). This is usually quite close to the mark.

Assessing your APC

You can create a target APC range when you are in a steady state situation.

• Minimum pasture cover = (target pre-grazing cover + optimum grazing residual) ÷ 2
• Maximum pasture cover = (maximum pre-grazing cover + grazing residual) ÷ 2

Using a maximum and minimum average pasture cover for the farm helps ensure plans are feasible while ensuring pasture quality remains within an acceptable limit and cows continue to consume target intake.  It is a great tool to have on a board in the dairy shed to monitor grazing events with the rest of the team.

Pasture growth rate does not remain constant, nor do rotation length and cow feed requirements. So your minimum average pasture cover will change during the year to reflect changes in target pre-grazing and post-grazing yields.

Similarly, maximum average pasture cover will reflect the maximum pre-grazing cover desired at a time of year. When considering maximum pasture cover, your concern is to maintain pasture quality rather than cow intake.

Managing maximum cover is important as pasture quality deteriorates under high pasture covers.

APC targets

Average Pasture Cover targets are important for managing pasture supply. Working to achieve key APC targets will either help ensure there is enough quality feed ahead of the cows or to ensure pasture supply in the following season.

• Achieving your APC target at balance date is important to ensure that the cows have sufficient high quality pasture in peak production months. 
• Achieving your target APC at calving is important for meeting feed demand, and for pasture growth rate and quality. APC at calving will determine how cows are fed for the first two months after calving.
• Having an APC target at dry off is important for transferring autumn grown pasture into early spring. The average pasture cover target is achieved during autumn by increasing rotation length and reducing herd demand (culling, drying off).

APC at Calving

The level of pasture cover at calving is very important. Too much feed will mean that pasture is wasted and growth may be reduced. If there is insufficient pasture, the cows will be underfed and pasture growth reduced.

If there is insufficient pasture the inter-grazing interval is reduced, resulting in pastures being grazed before the 2½ leaf stage. Pasture growth will be reduced and pasture cover will stay low until the summer.

Therefore average pasture cover (APC) at calving (and supplements available) determine how well  cows are fed for the first two months after calving.

This page covers what you can do if APC is below target at the start of calving.

Calculating the required APC at calving

• APC is determined by calving rate, cover at balance date and strategic decisions about use of supplements. For most farms this APC target is between 2200 and 2400kg DM/ha.
• A formal feed budget is often not required if there is enough knowledge from previous years to determine APC at calving and balance date.
• If you are on a new farm a feed budget will help determine the amount of feed required (cover, grazing off, supplements) and predict APC at calving.
• Feed budgeting is a prediction based on best available knowledge. Therefore gather as much information as possible about the farms growth rates, soil temperature, nitrogen application, conditions that may cause feed wastage and feed intake estimates.

If APC is below target

• Face your situation - walk the farm, confirm the size of any deficit and develop a plan on how to fill the deficit for the next two weeks
• Share your plan
• Seek advice
• Continue to monitor actual pasture cover weekly and adjust plan weekly or fortnightly if necessary.

Create a plan

Think about whether you can grow more pasture?

• Apply nitrogen
• Minimise pugging
• Slow the rotation (feed supplement) to increase APC as quickly as possible.

Can you increase feed supply?

• Reduce wastage to make reserves last longer
• Buy in additional feed

Or reduce feed demand and slow the rotation?

• Lower stocking rate (if possible get later calvers or dry stock off the farm)
• Prioritise stock and check intakes, cow intake at calving is significantly less than peak intake.

Related publications

APC at balance date

Achieving the target average pasture cover (APC) at balance date is important to ensure that the cows have sufficient high quality pasture in peak production months and during mating.

• Balance date is when pasture growth rate increases to meet feed demand.
• Balance date should have the lowest average pasture cover (APC) of the season.
• Setting target balance date APC in the range 1900-2100kg DM/ha should ensure cows are adequately fed while maintaining good quality throughout the following months.
• Balance date APC can be calculated, then the number checked against these factors:
  • Stocking rate/feed demand – high vs low
  • Predictability of pasture growth after balance date – reliable v unreliable
  • Rotation length - faster or slower
  • Controlling surplus feed after balance date – focus on maintaining quality v shifting feed to another period to fill a deficit

The Importance of Average Pasture Cover at Balance Date

• If average pasture cover is too low cows will be underfed and pasture growth reduced.
• If average pasture cover is too high, pasture quality will decline later in spring and production will suffer when cows are forced to graze to a lower residual than a previous grazing.

Target average pasture cover is dependent on the stocking rate and the pasture demand per cow (influenced by days since calving, production, breed and supplement fed). This should be the lowest that APC will reach all year and most farmers will set it within the range of 1900 – 2100 kgDM/ha.

Pasture cover targets and rotation length targets outside this range should be managed carefully.

Balance date is when pasture growth rate increases to meet feed demand.

APC at balance date is required to set up the Spring Rotation Planner (SRP). The SRP is then used to monitor actual pasture cover against target pasture cover, allowing rotation length to be sped up or slowed down to bring the farm’s average pasture cover back on target.

Is your balance date APC number sensible for your farm?

Take care interpreting this figure, as the calculation can signal pasture cover targets and rotation length targets that are not appropriate for good management (i.e fast rotations for low covers, and slow rotations for high covers are not appropriate management at balance date).

Other considerations for your balance date cover include:

• If your stocking rate and/or pasture growth rate pattern mean that supply will be much larger than demand during the peak spring growth, set your APC at the low end of the 1,900-2,100 kgDM/ha range; and
• If your spring growth after balance date is unreliable, set your APC at the higher end of the 1,900-2,100 kgDM/ha range.

Ensure your fastest rotation length, used in this balance date APC calculation, is appropriate for optimum pasture growth and suits your farm system. The rotation length at balance date is usually 20-25 days. Lower stocked farms or farms using high amounts of supplements may go to an 18 day round. Farms that are subject to very volatile growth rates (one week 80 kg DM/ha the next week 20 kg DM/ha) tend to have a slower rotation (23-25 days) at balance date, as do high stocked farms.

For a discussion on rotation lengths in relation to ryegrass leaf stage click here.

Factors to consider for your farm

Worked examples of balance date APC targets for two situations

High Stocking rate= feed demand of 50kg DM/ha or more at balance date (3.1 cows/ha x16 kg DM/cow = 50 kg DM/ha /day. Rotation length 23 days= 2075 kg DM/ha average pasture cover)

Low stocking rate= feed demand of 42 kg DM/ha/day or less at balance date=(2.6 cows/ha x16 kg DM/cow=42 kg DM/ha. Rotation length 21 days= 1937 kg DM/ha average pasture cover)