Cut early and cut often

4 May 2020

After the middle of May, every week delay in cutting up until the middle of June results in grass losing three units of dry matter digestibility and delays second cut by two weeks.

Therefore, each week delay in cutting could reduce potential milk from forage by greater than 1.0 litre/cow/day.

Making subsequent silage cuts at no more than 6 week intervals will maximize quality of forages and set a farm up for a very cost-effective winter feeding period. Further advice on maximizing grass quality include:

Ensure ‘free nitrate’ level is below 1,000mg/kg (0.1%) in the freshweight before cutting

The free nitrate value indicates the nitrogen fertiliser that has not yet been converted into protein in the grass. Free nitrates increase the buffering capacity of silage, which will slow the fermentation process, allowing for greater loss of nutrients and undesirable bacteria to multiple before a stable pH is reached. Additionally grass silage tends to be less palatable and less stable at feed out (i.e. at risk of secondary fermentation).

A ‘free nitrate’ level between 1,500mg/kg (0.15%) and 2,500mg/kg (0.25%) in the fresh weight, is acceptable and effects on fermentation marginal provided the optimum dry matter (28-30%) and sugar level can be achieved in grass. Cutting should be delayed if ‘free nitrate’ level is above 2,500mg/kg (0.25%) in the freshweight. If this occurs retest again in 2-4 days.

Free nitrates can be tested in the laboratory and results received within 24-48 hours or tested on-site using nitrate testing strips.

Ensure sugar level is at least 3% in the fresh weight or 10% in the dry matter before cutting

The higher the sugar the better the fermentation and the quicker a stable pH can be achieved, hence, conserving as much of the nutrients in the clamp as possible. Grass sugars will be low in cases where free nitrate is high. Allowing time for nitrates to be used up in grass will also help to increase sugar level. Cutting in the sunshine and delaying cutting until the afternoon when sugars in grass are typically highest, combined with a rapid wilt (<24 hours) will help to concentrate the sugars for ensiling. 

Sugar levels can be tested in the laboratory and results received back within 24-48 hours or tested on site using a refractometer (same device used for testing colostrum quality).


The main reason for using an additive should be to improve fermentation quality to retain as much of the feed value in the clamp as possible. The need to apply an additive to address concerns over aerobic stability can often be avoided by good ensiling and feeding-out management practices. However, in some circumstances outside a farmers control where aerobic spoilage could be an issue (e.g. feeding out during summer) an additive that improves fermentation quality and reduces aerobic spoilage should be used. If applied correctly silage additives are typically cost effective even with excellent grass quality and ensiling conditions.

Where grass dry matters are optimal (28-30%) and ensiling and feed out management good a chemical additive or homofermentative bacterial inoculant can be used. In cases where aerobic spoilage could be an issue a chemical additive alone or chemical plus homofermentative bacterial inoculant combination is advised. In cases of low grass dry matters (low 20’s), low grass sugars, residual nitrogen or slurry contamination a chemical additive is advised. For slurry contamination use a chemical additive containing nitrite to inhibit undesirable bacteria (clostridia & enterobacteria) which can be present on slurry.  When using bacterial innoculants ensure the product provides a minimum of one million bacteria per gram of grass.