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Silage. The Power of Forage

Updated: Jul 24, 2023

Here at Hillhead of Covington we aim to do 4 cuts of grass silage for the milking herd, sometimes 5.

Silage is the main part of our milking cows diet throughout the year. Here in central Scotland we can grow large quantities of good quality grass to make into silage. We want a stable consistent product that can be fed throughout the year. The higher the energy and protein content that we can have in our grass silage the less feeds we need to purchase.

We aim for a dry matter of around 30%, ME (Metabolisable Energy) >11.5MJ/kgDM, crude protein >15%, D Valvue (digestibility) >72%, PH >4.

Good Quality Grass

The most essential element for making good quality grass silage is having good quality of grass. We use a perennial rye grass mix of intermediate and late heading varieties. We aim to reseed our grass fields around every 7 years as we find this is a good means of keeping the grass young and the varieties most prolific whilst running a cost effective reseeding policy. Grass plant research and advances in variety breeding are constantly improving.

Cutting the grass at the correct stage

We ideally want to cut (mow) before seed heads start to appear as once the grass starts to produce seed heads the energy content and digestibility start to decrease rapidly.

Getting it Dry

We want to scatter the grass across the field as soon as possible after mowing to allow for a rapid wilt. We aim to dry the grass and lift it within 24 hours of mowing as after the grass is cut it starts to loose energy. We need it dry but not dead. On average growing grass is around 15% dry matter (DM) and we are aiming for 30% dry matter so its important to get it dried. When wet grass (<25% DM) is made into silage, the excessive water is turned into acid and it makes the silage acidic, which is not good for cow nutrition and health.

Raked and Lifted

The grass is then gently raked into rows. At this stage its important not to rake the ground and contaminate the grass with soil. We use a forage wagon to lift and chop the grass into 15mm lengths. Chopping the grass makes it easier to handle and compact into the clamp and thereafter handle to feed. At 15mm lengths, the grass retains structural fibres which is essential for good cow rumination.


Once the grass reached the clamp we want to fill the clamp and compact the grass in layers. We use a tractor and silopactor to maximise compaction. The tighter we can compact the crop the more air/O2 we remove from the grass and the more grass we can fit in.


As soon as the last load of grass is in we want to get the clamp covered and sealed as quickly as possible. Firstly we use a clear plastic clingfilm like sheet to tightly cover the grass, then we cover with a heavier black plastic sheet which provided a second cover and is more robust. We then cover with a heavy green net to protect the plastic and hold it down. We then have to put on heavy tyres and gravel bags to stop the covers being blown off on windy days. It gets pretty windy up here at the top of the hill!


In order for the grass to become silage it has to go through the fermentation process. This requires an anaerobic (no oxygen) environment. A rapid fermentation increases the quality and stability of the grass in the clamp. Silage is usually best left for 6 weeks before eating but can be fed sooner if required.


The weather is highly important when making silage. As we want to cut the grass at the right time and the process takes 3-4 days, sometimes 3-4 dry days just don't happen!

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