Dairy Farming:
How to See and Deal with a Pasture Silage Surplus

by Matt Bartleet


As we are now into the pasture growth exceeding pasture demand period, a refresher on how to identify and harvest pasture silage is a good idea. Pasture silage harvests can simply be estimated by eye but to add a degree of accuracy and measurability to the harvest, the following is a simple and effective technique.

The best way to identify a pasture silage surplus is to conduct a pasture cover assessment (using a plate meter or other pasture measurement techniques). Once each paddock is assessed, each paddock that is above your target pre graze level can be skipped for silage.

Its good to ‘skip’ smaller areas at a time. This minimises the risk of skipping too much at once and reducing milk production. These smaller areas can accumulate into a larger harvest over time by repeating the process at each pasture cover assesment, or can be taken as a small harvest. If it is difficult to get the contractor to come at the right time, smaller harvests allow more grass to grow in the small area, while maintaining quality on the remaining area. (The silage harvested will likely be at lower quality though).

When ever possible, try to cut silage off your effluent paddocks. They are likely to have the highest growth rates and wont require replacement fertiliser after cutting. It also helps to lower their nutrient levels and spread it back out over the rest of the farm as you feed the silage.

The process of pasture becoming silage uses some of the energy in the pasture. So whatever level of energy pasture goes in to the stack/bale will come out as lower quality as silage. Often we are guilty of waiting to get a ‘bigger stack’ by leaving the pasture grow for a few more weeks, but seeing the grass and therefore silage quality decline rapidly. Think of what the intended destination of silage is. If is a milking cow still producing good levels of milk, do you really want to feed her low quality silage?

Silage surplus calculations:

You need: Example
Effective Farm area and paddock numbers 100ha/36 similar size paddocks of 2.7ha
Cow numbers/stocking rate 320/3.2cows/ha
Current rotation length/area used per day 24days/4.17ha/day
Pre graze target cover 2900kgDM/ha
Post graze target residual 1500kgDM/ha
Pasture feed level target 18kgDM/cow/day
A farm walk feed wedge (and how many pads above pre graze target cover) 6 pads above 2900kgDM/ha
The pasture growth rate 70kgDM/ha/day

How to adjust round length after skipping silage paddocks

1. Skip the paddocks above target pre graze cover 6 pads at 2.7ha = 16.2ha
2. Decide to keep round length at 24 days OR ‘speed up’ Keep at 24 days
3. New area of farm being used to milk off 100 – 16.2 = 83.8ha
4. Calculate new area used per day 3.49ha/day
5. Calculate per ha DM required (320 x 18)/3.49 = 1650kgDM/ha
6. Calculate new pre graze target 1650 + 1500 = 3150kgDM/ha

This calculation shows that after shutting up your silage area, you can adjust the pre graze target to a higher level to maintain the round length (or days it takes to reach maximum growth rates) and still feed cows target levels of pasture DM.

You can also work out how many hectares to be skipped based on growth rates. This is a good way to confirm the area you have skipped is appropriate (and help show that your feed wedge is ‘normal’).

Area of silage to cut

1. Calculate daily feed demand 320cows x 18kgDM/cow/day = 5760kgDM/day
2. Divide daily demand by known growth rate (eg 70kg/ha) (5760kgDM/ha/day)/70kgDM/ha/day = 83ha
3. Take this area off the total area 100ha – 83ha = 17ha

The calculation shows that the cows can still be fed the same with 17ha skipped out for silage.

Over the 2 calculations, our example shows that 6 pads above target pre graze residual can be skipped for silage, being a total of 16.2ha, this is confirmed with our second calculation, which shows that 17ha can be skipped.

If you don’t have a feed wedge, a pasture silage surplus can still be identified. It still requires assessing pre and post graze pasture covers, but you can do that as you look at paddocks before the cows go there.

How to identify and skip silage paddocks without a pasture cover feed wedge

  1. Look at next 3 or 4 days of paddocks due to be grazed next.
  2. Skip them out and go to the paddock due while still meeting your pre graze target cover.
  3. Re-check the impact of your skipping ahead by checking the post grazing residuals. If they have fallen below your target, then you have skipped to much or not assessed the pre graze cover correctly. Go back and graze some or all of those paddocks.
  4. Repeat the skipping/checking process over the whole rotation.
  5. Once you have an area that you think is going to be cut, confirm it with the area of silage to be cut calculation (if you know your pasture growth rate). Or do the calculation backwards to make sure your area skipped doesn’t require an unrealistic growth rate.

Choosing the best way to store the silage is the next step.



Pit Silage

  • Can be lower cost and easy to feed out.
  • Does need a larger area to harvest enough silage to make pit silage.
  • The larger area required can lead to feed deficits due to slower pasture growth/regrowth.
  • The larger area required can result in reduced quality if some is left for too long.
  • There is a risk of leachate into waterways if the silage is harvested in wet conditions from your stack or pit.


  • Can be more expensive and can be labour intensive to feed out.
  • Can harvest smaller areas per harvest.
  • Smaller areas harvested can reduce the risk of creating a feed deficit due to pasture growth/regrowth.
  • Reduced risk of leachate into water ways.


  • A crop can be planted instead of harvesting surplus pasture silage.
  • Can be more expensive than harvesting silage.
  • Direct risk of crop failure.
  • Can be labour intensive to feed out.
  • Depending on the crop, can limit feeding dates.
  • Can be useful to improve poor performing paddocks

Deferred Grazing

  • The pasture surplus can be left standing for grazing at a later date.
  • Low cost option
  • More date dependant (late surplus and early feeding dates).
  • Low quality feed and can be difficult to get cows to eat it.
  • Quality of pasture can drop markedly and may not be useful as a milking cow feed.
  • Ryegrass staggers risk.
  • Re seeding benefit to paddock.


  • The pasture surplus can be cut and left to rot away.
  • Only an option on some paddocks and farms.
  • A good option on lower stocked farms.
  • Helps keep quality but wastes grass.
  • Costs include diesel, R&M of machinery, time, depreciation.
  • Harder to deal with large surpluses.