With many farmers making their way through the second- or third-cut silage harvest in August, it is a good time to calculate your fodder stocks for the winter ahead.

With variable weather conditions during the past few months, it has not been ideal for grass harvesting, with short weather windows to get the silage in the clamp or wrapped in bales.

If cattle have had to be housed for periods during wet weather conditions, that will put further pressure on winter fodder stocks.

For dairy herds with cows indoors all year round, it is easier to calculate the fodder demands.

Ground conditions also influence how the silage will be harvested, as multiple trailers and machinery over bare ground can lead to tracks and compaction.

There has been good grass growth over the past few weeks and it is still not too late to make more silage.

Any surplus paddocks can be baled or a light fertiliser application could produce a decent silage crop in the second half of September.

An online calculator is available through DAERA Online Services to help with the calculations.

For those who wish to do the calculations by hand, a worked example is given below.

For example, a silo measuring 35 metres long by 12 metres wide with an average silage depth of 2.5 metres has a silage volume of 1,050 cubic metres (35 x 12 x 2.5).

To convert cubic metres of silage to tonnes of fresh weight, the calculated volume is multiplied by the appropriate conversion factor.

Assuming the silage analysis has shown a Dry Matter of 25 per cent, multiply the volume of 1,050 cubic metres by 0.68 to get 714 tonnes fresh weight of silage in the pit.

For 20 per cent silage dry matter, multiply by 0.77 to get tonnes of silage per cubic metre.

Once you have calculated how much silage you have, the next step is to calculate how much silage is needed.

Milking dairy cows require 1.4 tonnes of silage per month, while dry cows require slightly less at 1.4 tonnes, heifers up to two years old require 0.8 tonnes, and heifers under one year old just 0.6 tonnes.

To calculate the silage required, simply multiply the number of cattle to be fed by their monthly silage requirement, and the number of months the animals are likely to be housed.

On completion of this calculation, for all stock on farm, you can compare the silage requirements with silage stocks.

It is better to know if you are going to require additional forage early in the winter to secure additional supply before you actually need it, as prices will inevitably rise through the winter if there is a fodder shortage.

It is very important in any winter feed plan to get your forages analysed. This will give you a prediction of the silage intake potential, metabolisable energy (ME), crude protein, and dry matter content of the forage.

While it is important to get an initial silage sample analysed, you should also remember to get subsequent, representative samples analysed during the winter, as silage quality will vary through the pit.