Initial results for this year’s first cut grass silages suggest a poorer than average year and crops will require careful balancing to maximise the contribution from forage in winter diets.

The results based on more than 500 samples to include some from Scotland analysed at Trouw Nutrition's analytical laboratory in Ashbourne, reflect the growing season, according to Dr Liz Homer.

“The generally mild winter means many swards contained a higher proportion of over-wintered material," she said.

"During the spring, grazed grass samples showed a high fibre index and low acid load, reflecting higher NDF content and a similar situation was seen with pre-cut grass silage testing.

“This is now apparent in many of the silage samples seen so far with higher NDF content which is influencing nutritive content and also how forages will behave in the rumen and the type of supplementation which will be required. While some very good silages have been made, the average is only similar to last year and there must be concerns about quality in later harvested crops.”

Looking at the headline figures, Dr Homer says that on average crops are 30.7% dry matter compared to 33.7% last year. Crude protein is slightly higher at 15.3% while ME content is down from 11.7MJ/kgDM to 11.4MJ/kgDM. D value is 71.5% compared to last year’s 73.2%.

As a result, she said there is concern that these silages largely represent farmers who have adopted multi-cut systems where the emphasis is on more frequent cutting to improve quality. Higher lignin levels indicate that despite cutting sooner, farmers have harvested more mature crops. The numbers suggest quality this year is steady not spectacular, and it should be anticipated that when we see the numbers across the whole first cut season, results will be of poorer quality than these early averages, added Dr Homer.

“NDF is significantly higher at 46.1% compared to 41.8% which in part explains the lower ME levels. More than 50% of samples have an NDF level above 45% while the target is usually below 45% DM, around 42% DM. On a positive side the higher NDF means silages have a higher fibre index and reduced acid load which means they are safer for the rumen.”

Read more: Glenapp makes the most of its grass

Dr Homer added that higher NDF silages point to slower rumen throughput, which means feeds take more time to digest and in turn impact dry matter intakes and milk from forage. Looking at the way theses silages will ferment in the rumen, she says that while Total Fermentable Carbohydrate levels are higher, there is less Rapidly Fermentable Carbohydrate. At the same time Total and Rapidly Fermentable Protein are higher due to the higher crude protein. Therefore, it will be essential to balance fermentable carbohydrates and protein for an efficient rumen.

“Where grass was well-managed and fibre digestibility is good, the higher NDF content will mean there could be more energy available for the cow. However, in many cases it will be necessary to supplement these silages with Rapidly Fermentable carbohydrate sources such as cereals to accelerate rumen fermentation and balance the rumen to encourage fibre digestion, improve flow rates and encourage higher intakes.

“The crucial thing will be to get silages regularly analysed and to balance forages with energy sources that provide what the rumen requires. This way you will get the most from the silage in the clamp” she concluded.

Comparison of early first cut grass silages 2021 and 2022 (source: TNGB)

2022 2021

Number of samples 529 500

Dry matter (%) 30.7 33.7

Crude protein (%DM) 15.3 14.6

D value (%) 71.5 73.2

ME (MJ/kgDM) 11.45 11.71

NDF (%DM) 46.1 41.8

pH 4.09 4.2

Acid load 48.9 52.5

Fibre index 184.7 167.1

Dynamic Energy (MJ/kgDM) 6.19 6.05

Rapidly fermentable carbohydrates (g/kgDM) 194.7 215.9

Total Fermentable Carbohydrates (g/kgDM) 448.2 436.6

Rapidly Fermentable Protein (g/kgDM) 93.7 94.6

Total Fermentable Protein (g/kgDM) 112.5 108.5