Pre-Cut Monitoring of NDF Levels

NDF development of the grass crop offers a scientific basis to help optimise silage quality by informing 1st cut mowing decisions. To optimise 1st cut silage quality it is recommended to cut before the NDF content in pre-cut grass reaches 40%. To achieve this we recommend testing pre-cut grass (1st cut) weekly from mid / end of March to monitor NDF development and also provide information on sugar and free nitrate levels which are important in achieving a quality silage fermentation, as well as careful management of the ensiling process.

Pre-cut NDF Tracker

The graph tracks the average NDF development in samples processed through the Trouw Nutrition GB laboratory leading up to 1st cut. This is a national average and it is important to monitor the situation on individual farms through pre-cut grass testing. 

Final Report for 2023 Season


The final reporting period for 2023 pre-cut samples reveals an average NDF content of 47.1% DM, which is considerably higher than the target of 38-40% DM. A large range in NDF levels is still reported from 31.5-62.0% DM. This highlights the need for individual farms to analyse their grass to understand when to cut for optimal silage before quality is compromised. Average sugar levels have increased slightly this week 11.1% DM, although a large range from 4.1- 17.0% DM is
seen. A number of samples have dropped below 10% DM, which increases the risk of poor fermentation. If sugars are below 10% DM an additive designed for low sugar forage is recommended to ensure quality fermentation.

In summary, the Pre-Cut NDF Tracker 2023 reported that NDF content was very high and above optimum each week, without dropping below the target NDF unlike trends we have seen in previous years (except for weeks 11-13 where we received very few sample submissions). This is due to a very mild winter allowing grass to continue to grow and mature. Whilst this is the last time we will report pre-cut NDF content for 2023 we still continue to encourage submission of samples from any remaining silage crops to optimise cutting, as values will differ between farms and fields, as proven by the large variations in samples seen throughout the season.


It’s important for individual farms to send in pre-cut samples to accurately monitor grass development particularly as there have been very high NDF levels reported in the majority of samples received this season compared to previous years. Please ensure all details on the submission form are filled in, so we can accurately monitor trends and optimize our reports.


Please ensure all details on the submission form are filled in, so we can accurately monitor trends and optimize our reports.

Why monitor NDF development in silage fields?

Grass grows differently every year and silage quality is often reflective of the previous winter. Warm winters where soil temperatures remain above 8 degrees means grass will continue to grow and therefore is more mature. Mature grasses have a higher NDF content and are potentially more lignified earlier in the year, resulting in silages that are less fermentable which could lead to reduce rumen passage rates, lower feed intakes, and lower production when diets are not balanced. When we have seen a cold winter, the grass stops growing with low soil temperatures and the silage season is often later.

Read more about grass nutrient content

How do I take a representative pre-cut fresh grass sample to assess NDF content?

Take a representative Pre-Cut fresh grass sample that comprises of 10 sub-samples taken in an 'X' pattern across the area (two samples at each point on the 'X'). These should be cut with scissors at mower height and then placed into a sample bag.

Clearly label the sample bag with the customer name and sample reference, and complete a forage sample request form including: 

  • Your contact details
  • The full address for the farm including county
  • The sample reference
  • Tick the Pre-Cut grass testing box

Post the sample as soon as possible to the Trouw Nutrition GB laboratory.

N.B. Avoid sending samples on a Friday to avoid delays in the analysis if the sample is received over a weekend.

Pre-Cut Sample Video

How to take grass samples

A video explaining how to take grass samples for analysis at the Trouw Nutrition GB laboratory.

Contact Us

Our Ruminant team consists of:

Isabell England - Ruminant Nutritionist

Alicia Bexon - Ruminant Nutritionist

Mark Hall - Ruminant Technical Manager

Contact Us