Variable grass silage – regular analysis crucial for yields

Grass silage analysis of 1000first cut and 500 second cuts from Trouw Nutrition's analytical laboratory in Ashbourne, shows careful balancing will be required to maximise production.

Ruminant advisor, Nacia Bonnick said second cuts in the main tended to drier than first cuts reflecting better growing and harvesting conditions compared to the wet spring which affected first cuts. While second cuts will be palatable, but increased lignin and reduced rapidly fermentable carbohydrates mean these silages will need careful balancing.

“Compared to the earlier samples received, the main first cuts have slightly lower dry matter with lower D values and energy content. However, lower lactic acid and volatile fatty acid contents indicate that silages are well preserved.

“The results show lower levels of rapidly fermentable carbohydrates, but total carbohydrates are increased due to increased NDF content. Combined with a high fibre index this will reduce nutrient supply in the rumen.

“With some positive movement in milk prices combined with the easing of some commodity prices, it will be crucial to ensure silages are regularly analysed and then supplemented with purchased feeds that supply what the cow needs to fully utilise forages. This may mean more regular fine-tuning of diets throughout the winter and challenging all supplementary feeds, buying on effective nutrition rather than price.”

Looking at average first cuts, Ms Bonnick suggests that due to lower Total Fermentable Carbohydrate (TFC) and higher Total Fermentable Protein (TFP) levels they will need careful balancing with supplemental carbohydrates to balance the higher TFP and ensure optimal microbial protein production and protein efficiency. Conversely second cut is higher in TFC and lower in TFP, meaning they are better balanced than first. Consequently, balancing should be slightly easier.

“Acid load and Fibre Index values mean both first and second cut silages look safe to feed and should promote reasonable levels of butterfat without the need for huge amounts of additional buffer. Given the higher fibre index in both cuts, especially first, it will be vitally important to ensure rapidly fermentable carbohydrates are added in to the diet to optimise rumen function alongside rapidly fermentable protein to maximise microbial protein production.”

She advises keeping a close check on dry matter as fluctuations can significantly affect ration potential. “If the dry matter of the clamp differs from the dry matter used to calculate the diet, the nutrients supplied will differ significantly. For a cow targeted to receive 12kg silage DM, a 3% reduction in silage dry matter will reduce energy supply by the equivalent of one litre of milk meaning the ration will need rebalancing.

“The better picture you have of silages this year, the more effectively you will be able to formulate cost-effective diets to meet your objectives. Central to this will be regular analysis of all opened clamps, at least monthly, combined with detailed assessment of the most effective supplements,” Ms Bonnick concludes.

Average 2024 first and second cut grass silages (source: TNGB)

1st cut 2024 2nd Cut 2024

Units Average Average

Dry Matter % 33.7 34.7

Protein % DM 14.4 13.5

D Value % 68.6 68.3

ME MJ/kg DM 11.0 10.9

NDF % DM 46.7 47.0

ADF % DM 29.7 30.0

Lignin g/kg DM 38.4 37.1

Sugars % DM 1.7 2.3

pH 4.1 4.2

Lactic Acid g/kg DM 84.9 70.8

VFA g/kg DM 24.9 26.1

Ammonia % 3.3 3.1

Rapidly Fermentable Protein g/kg DM 88.0 82.7

Total Fermentable Protein g/kg DM 103.4 97.0

Rapidly Fermentable Carbohydrates g/kg DM 190.9 195.9

Total Fermentable Carbohydrates g/kg DM 434.2 449.6

Acid Load 47.5 47.3

Fibre Index 186.7 188.7