Silage cutting is in full swing again this week as the sunny spells and settled weather conditions have provided an ideal chance for farmers to secure additional fodder in the form of bales or pit silage. However, many farmers are asking themselves if they have enough silage in the yard to get them through the winter housing period of livestock. In more recent times, the duration of winter housing has become more unpredictable and farmers should make an allowance for a late spring when doing their fodder budget. Before putting together a fodder budget, it is important to know the following:
  • Volume of silage in the pit;
  • Number of cattle to be wintered on farm;
  • What feed will each animal be receiving.
When calculating what weight of silage is in a pit, the following calculation will give farmers an approximate indication of the amount of silage available (in tonnes).

Calculating how much silage is in your pit:

  • Step 1: Measure the length, width and height of pit in metres;
  • Step 2: Multiply length x width x height = total silage area available;
  • Step 3: Estimate the dry matter (DM) of your silage;
  • Step 4: Multiply the total area by either 0.68, 0.77 or 0.81 (depending on silage DM);
  • Step 5: Calculate how long the silage will last for the animals on your farm.

If the silage is 18% DM, multiply the area by 0.81. If it’s 20% DM, multiply by 0.77 or if your silage has a DM content of 25%, you will need to multiply the area by 0.68 to calculate how much silage is actually in your pit.

E.g. assuming a farmer had a silage pit with an average pit height (3m) x pit width (10m) x pit length (30m) = area (900m³). If the silage has an estimated DM of 25%, the amount of silage available = 900 x 0.68 = 612t fresh weight (FW).

How long will fodder last?

How long the silage will last depends on the type of animals present on your farm and how much of the feedstuff they will eat over the winter months. E.g. a suckler cow will eat 1.4t/month and a weanling will eat 0.7t/month. If a farmer has 50 cows and 40 weanlings, the calculation would be (50 x 1.4) + (40 x 0.7) = 98t/month requirement. Divide the total available silage by the monthly requirement to calculate how many months of feed is available. So, 612t of silage divided by 98t/month requirement = 6.2 months worth of silage. The table below gives an approximate estimate on the weight of silage each livestock type will consume each month. However, it is important to remember that the figures can vary significantly depending on the quality of the silage and the weight and size and condition of the animal.
Animal type t/month
Dairy cow 1.6
Suckler cow 1.4
In-calf heifer 1.3
Weanling 0.7
Store cattle 1.3
Where bales are being used as opposed to pit silage, Teagasc has outlined that a 220 kg DM bale is equivalent to one tonne of pit silage at 22%DM. For example a single bale of the above quality will feed 20 dry cows for a day. Farmers should remember there is huge variation in both bale and pit sizes, weights and dry matters and should allow for this when planning and determining if they will have sufficient fodder for the winter or not.
FODDER SILAGE