Forage stocks

Published 2 August 13

Carrying out an assessment of grass silage stocks now will help you manage forage stocks throughout the coming winter, and allow strategies to be implemented to help address any potential shortfalls, says DairyCo extension officer Tom Goatman.

For clamped silage, the available stock is calculated by working out the clamp volume (m3) and then multiplying this by the silage density (kg/m3).

To calculate the volume (m3) of the clamped material, multiply the length (m), width (m) and height (m) of the clamp. Adjustments will need to be made for the ramp, if present, or sloping sides as found in field clamps or Ag-bags.  See diagram

Apply the same technique as used in the ramp assessment to calculate field or Ag-Bag clamp volumes.

Once the volume of the clamp has been calculated, a good estimate of the density of the grass silage can be derived from the silage DM and clamp height as set out in table 1.

If all the groups’ grass silage intakes are totalled, this will then give you the daily grass silage DM requirement. To estimate the number of days of supply left in your stocks, divide the total clamp silage dry matter available to feed (kg) by the daily requirement (kg).

It is important to note that these calculations only provide an estimate. It is difficult to accurately predict how long the winter will be or the actual animal intakes. It is therefore helpful if a small surplus is achieved to allow a buffer if the winter is prolonged. Calculation of your current grass silage stocks will also help give you an estimation of the performance required from other forage crops, such as whole crop wheat and maize, that may also make up the forage component of the winter diet.

If a potential issue with forage supply is highlighted, management areas to consider may include:

  • Growing more forage over the remainder of the season if circumstances allow
  • Making use of buffer crops such as stubble turnips
  • Sourcing forage externally to your own farm
  • Reducing stock numbers carried through the winter.

Further information including worksheets to calculate forage stocks, requirements and feed costs are available in DairyCo Feeding+. To request your copy please contact your local Extension Officer or visit