My silage pit is disappearing; how can I calculate if I have enough?

Winter feeding is well and truly underway. An extended grazing period – after the 2018 summer drought – allowed farmers to boost fodder supplies, while also leading to a late housing in some cases.

However, some farmers have reported that their silage supplies have started to dwindle in recent weeks. Farmers who think they will be short silage should calculate how much silage they have left using the Teagasc guide.

While no one knows how long the winter will be, it is advisable that farmers know exactly how much silage they have.

Measuring pit silage on your farm

According to Teagasc, to calculate the amount of silage in a pit, farmers must first measure the length, breadth and height of the clamp.

Once measurement is complete, farmers will have the area (m³) of silage available and can then estimate the quantity of fresh-weight silage available (tonnes) using a simple calculation.

Over or underestimating feeding value due to a lack of test results can cost you a significant amount of money.

If a forage is not analysed, then farmers will either underestimate or overestimate the amount of meal and/or silage required by stock in order to secure optimal animal performance. Therefore, testing is very important.

This calculation depends on the dry matter (DM) level of silage and, as a rough guide, farmers with supplies of good-quality, drier silage need to multiply the total available area by either 0.77 (DM 20%) or 0.68 (DM 25%).

Farmers with very wet silage (DM 18%) need to multiply the area available by 0.81, but given the summer that passed, this will be non-existent in the majority of cases.

Calculating how much silage is in your pit:
• Multiple the length x breadth x height = total silage area available;
• Estimate the DM content of your silage;
• Multiple the total available area by either 0.68, 0.77 or 0.81 (depending on silage DM);
• Calculate how long the silage will last the animals on your farm.

For example, silage height (3.5m) x silage width (8m) x silage length (20m) = silage area (560m³). Assuming the silage has a DM content of 25%, the amount of silage available is: 560m³ x 0.68 = 380.8t (fresh weight).

Converting bales to tonnes

A lot of suckler farms will have both pit and baled silage. According to Aurivo, to calculate the tonnage of silage available from bales, farmers should multiply the number of bales by 600kg (normal) or 700kg (well-packed).

Therefore, assuming the bales were well-packed, 40 bales would be the equivalent of 28t of silage (fresh weight).

When both the pit and bales are considered, it means that there’s 408.8t of silage fresh weight available on this theoretical farm.

How long will the supplies last?

The requirement for silage on farms will vary depending on the system. Different types of animals – at various ages – require different amounts of silage. The table below outlines the amounts of silage required by animals.

Example: How much silage is required for 50 suckler cows, 10 in-calf heifers and 48 weanlings?
• Suckler cow requirement (per cow): 1.4t/month;
• In-calf heifer requirement (per heifer): 1.3t/month;
• Weanling requirement (per weanling): 0.7t/month;
• Herd requirement ((1.4t x 50) + (1.3t x 10) + (0.7t x 48)): 116.6t/month.

Once the monthly requirement has been calculated, the farmer will then be able to judge how long it will last by dividing the total available by the monthly requirement.

408.8t (total silage available) / 116.6t (monthly requirement) = 3.5 months of silage.