The ideal chop length 

Chop length is important for the production of high quality silage. Dr Dave Davies of Silage Solutions Ltd discusses the ideal chop length. 

Whether the forage is destined for bales, clamps, pits, towers or sausage silos it should be chopped. Chopping improves the speed of fermentation, by releasing sugars and removing oxygen. In doing so, dry matter losses are reduced and silage nutritive value increased. 

In recent times there has been some debate about the ideal chop length for rumen health. In this respect a useful gauge for chop length is that it should be the width of a cow’s mouth! However, only a maximum 10 per cent should be this long. If there is too much long chopped forage cows will sort the ration and only eat the short chop. In terms of good compaction in a silage clamp it is absolutely essential to alter the chop length depending on the dry matter content of the forage to be ensiled. 

So what is the ideal chop length? 

The most important aspect of the chop length for silage clamps is the ability to sufficiently compact it in the silage clamp. This ensures the removal of oxygen allowing rapid fermentation to commence as quickly as possible. The higher the dry matter the more difficult compaction becomes and so the shorter the chop length needs to be. For these reasons it is essential to monitor the Dry Matter content of forage entering the silage clamp and alter chop length accordingly. The Table below provides a gauge. 

DM of Silage  

Ideal Chop Length 

>37% 

1 – 2cm 

32 - 37%  

2.5cm 

28 – 32%  

2.5 – 5cm 

22-28%  

8cm 

<22% 

8 – 10cm 

 

Suggested chop length required for good compaction of forages with different dry matter contents. 

A special note regarding Forage Wagons 

Forage wagons have become increasingly popular across many farms due to their lower running costs and the perception that longer chop material is better for rumen health. However, there is a tendency for forage to pass through the knives within forage wagons. Additionally, many old, badly maintained machines are used with knives that are not sharp. Hence a lot of the forage passes perpendicularly between the knives and remains unchopped. This gives rise to:- 

1. Long material in the silage clamp which is difficult to compact and traps oxygen 

2. Sugar not being released from the plant to aid a rapid pH decline. Together these result in a slower fermentation with higher nutrient losses and silage with higher levels of undesirable fermentation products such as acetate, butyrate and ammonia. This leads to lower palatability and intake potential. 

Checklist 

• Have a target DM of forage entering the silage clamp of between 32 and 35% DM 

• Check the DM and chop length in the first load brought to the clamp 

• Adjust chop length if necessary 

• Monitor DM content at least every 2 hours during harvesting as it can change depending on sun and wind. Adjust chop length accordingly