How to calculate how much silage you will need


To reduce feed costs, the aim should be to make top-quality silage

How to calculate how much silage you will need

  • ADDED
  • 27 days ago

To reduce feed costs, the aim should be to make top-quality silage

Most farms are likely to have sufficient quantities of silage in store for the winter ahead, writes CAFRE’s Nigel Gould.

However, it is advisable to determine the quantity and quality of silage in-store and use this information to develop a feed plan for the different classes of stock.

Year-on-year silage analyses show a wide variation in quality between farms and sometimes even within the one farm.

High-quality silage should be prioritised towards animals such as weanlings, lactating suckler cows and housed ewes in the final six to eight weeks of pregnancy. Poorer quality silage is sufficient for animals with a lower nutrient requirement such as dry suckler cows.

Make top-quality silage

Feed accounts for the largest proportion of costs during the winter period. To reduce feed costs, the aim should be to make top-quality silage as this will reduce the quantity of more expensive concentrates required.

If silage quality is poorer than usual, additional concentrates may be required to make up the deficit. After you have the silage analysed, use Tables 1 and 2 to estimate the quantity of silage available and compare this with your likely winter demand.

The volume of silage is calculated by multiplying the length of the pit by the width by the height. For example, the volume of silage in a pit measuring 40 m by 10 m by 3 m is 1,200 cubic metres.

To convert the volume of silage to tonnes, multiply the volume by the correct conversion factor (Table 1). For example, if the silage dry matter is 25% multiply 1,200 by 0.68; this equates to 816 tonnes of fresh silage.

Silage harvested in damper weather conditions this year is likely to have a lower dry matter compared to silage harvested during the dry spell experienced last year. For example, on a weight basis only 1.0 tonne of fresh silage with a dry matter of 30% is equivalent to 1.2 tonnes of fresh silage with a dry matter of 25%.

In reality, very low dry matter silage also tends to have poorer fermentation leading to poorer overall quality, compared to silage with the target of 30% dry matter content.

Table 1: Conversion factors to convert silage volume to tonnes of silage:

Silage DM %

Tonnes of silage/cubic metre

20

Multiply by 0.77

25

Multiply by 0.68

30

Multiply by 0.60

40

Multiply by 0.48

To estimate the silage demand of your herd, multiply the number of each class of stock by the number of months to be fed by the monthly feed requirement (Table 2).

Table 2: Estimated monthly feed requirement of stock consuming 25% dry matter silage:

Livestock

Silage (tonnes/month)

Dry spring-calving suckler cow

1.0

Autumn-calving suckler cow

1.2

350 kg+

1.0

250-350 kg

0.8

200-250 kg

0.7

Calves

0.3

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