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.
Managing pre-grazing yield and leaf stage
- Having an effective grazing management method (like the decision making process above) 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).
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.
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 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.
What is a 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 are higher for pasture species which have a higher crown e.g. tall fescue, cocksfoot.
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. Growth rate data (see Regional pasture growth data and the Pasture Growth Forecaster) is available for different regions however these are best used as a guide for strategic planning.
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
Average Pasture Cover (APC) 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.
For more information on calculating APC and setting targets see the Average pasture cover page.