Average pasture cover

Understanding average pasture cover

Average pasture cover is a key indicator of feed on hand and is the most reliable way of feed budgeting in the short term. Knowing the amount of pasture on hand, through regular pasture assessment, enables short-term tactical decisions to be made with relative confidence.

Maintaining average pasture cover above 1800 kg 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 down in response, 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. See here for more information on leaf stage.

By observing changes in pasture cover on a week-by-week basis, you are in a good position to respond to changes in average pasture cover before they become critical.

Average pasture cover is found by dividing the 'pasture cover x area' by the 'total area'

Rapidly estimating average pasture cover

If you have many paddocks, estimating the average pasture cover can take several hours. It can be estimated roughly by taking the average of the five paddocks with the most feed and the five paddocks with the least feed. This is usually quite close to the mark.

Assessing your average pasture cover

You can create a target average pasture cover range when you are in a steady-state situation.

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

Using a minimum and maximum average pasture cover for the farm helps ensure pasture quality remains within an acceptable range and cows continue to consume target intakes. 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. Your minimum average pasture cover will be adjusted during the year to reflect changes in pre-grazing targets and post-grazing residuals.

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

Managing maximum cover is important as pasture covers result in reduced pasture quality, increased disease, decreased pasture utilisation and reduced clover content due to shading.

Average pasture cover targets

Average pasture cover targets are important for managing pasture supply. Working to achieve key average pasture cover targets will help ensure there is enough quality feed ahead of the cows and ensure pasture supply in the following season.

• Achieving your average pasture cover target at balance date is important to ensure that the cows have sufficient high-quality pasture in peak production months.
• Achieving your target average pasture cover at calving is important for meeting feed demand, and for pasture growth rate and quality. Average pasture cover at calving will determine how cows are fed for the first two months after calving.
• Having an average pasture cover 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 (e.g. culling, drying off).

Average pasture cover at calving

The level of pasture cover at calving is very important. Too much feed will mean that pasture is wasted and feed quality declines.

If there is insufficient pasture, the cows will be underfed and pasture growth reduced. When average pasture cover is too low, 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.

Calculating the required average pasture cover at calving

• Average pasture cover at calving is determined by calving rate, cover at balance date and strategic decisions about use of supplements. For most farms this 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 average pasture cover 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 average pasture cover 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 average pasture cover 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.
• Seek advice from a consultant, experienced mentors, or find advice and support in the business section of our website.
• Monitor actual pasture cover weekly and adjust plan weekly or fortnightly if necessary.

Create a plan

Can you can grow more pasture?

• Apply nitrogen at appropriate times and rates
• Minimise pugging
• Slow the rotation by feeding supplement to increase average pasture cover as quickly as possible.

Can you increase feed supply?

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

Can you 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.

Average pasture cover at balance date

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

• Balance date is when pasture growth rates match feed demand.
• Balance date should have the lowest average pasture cover of the season.
• Setting target balance date average pasture cover in the range 1900-2100kg DM/ha should ensure cows are adequately fed while maintaining good pasture quality throughout the following months.
• Balance date average pasture cover 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 vs unreliable
  • Rotation length - faster or slower
  • Controlling surplus feed after balance date – focus on maintaining quality rather than moving 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 as cows will be forced to graze to a lower residual than a previous grazing.

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 average pasture cover number sensible for your farm?

Take care interpreting this figure. The calculation can signal pasture cover targets and rotation length targets which are not recommended for good pasture management, such as fast rotations for low covers and slow rotations for high covers.

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 average pasture cover target at the low end of the 1900-2100 kgDM/ha range; and
• If your spring growth after balance date is unreliable, set your average pasture cover target at the higher end of the 1900-2100 kgDM/ha range.

Ensure your fastest rotation length, used in this balance date average pasture cover 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 (e.g. 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.

Worked examples of balance date APC targets for two situations

High stocking rate example:

Feed demand of 50kg DM/ha at balance date (3.1 cows/ha x16 kg DM/cow = 50 kg DM/ha /day) x rotation length of 23 days= 2075 kg DM/ha average pasture cover target

Low stocking rate example:

Feed demand of 42 kg DM/ha/day at balance date (2.6 cows/ha x16 kg DM/cow=42 kg DM/ha) x rotation length of 21 days = 1937 kg DM/ha average pasture cover target