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Delaying silage cutting date will have a negative effect on quality and quantity

Delaying silage cutting date will have a negative effect on quality and quantity

James Dunne, Teagasc Dairy Specialist, outlines the reasons why you should avoid delaying silage harvesting and looks at the quality of silage needed on dairy farms this year.

Grass silage makes up around a quarter of the annual feed budget on the average dairy farm. We know where land type is heavy and/or dairy grazing stocking rates are high, this could be closer to one third of annual feed intake.

With high levels of rainfall and poor grazing conditions throughout March and into April, silage reserves have become depleted on many farms. One common question currently is 'should silage cutting date be delayed' to allow first cut crops to bulk?

It is important to consider the yield of forage dry matter across the year as a whole, not just from a single cut. Using a ‘one big first cut’ approach to make silage increases the risk of fodder shortages because second cut yields and annual grass production are reduced by pushing first cuts into mid-June.

Management decisions around first-cut silage yield should be made on the basis of meeting DMD (dry matter digestibility) targets and improving annual grass tonnage per hectare, rather than focusing solely on the bulk of an individual cut. Table 1 outlines typical quality targets and corresponding expected DM yields for first-cut silage crops. Differences in yield due to cutting date will generally be offset by heavier second-cut crops on swards cut earlier for first cut. In some circumstances (e.g. silage-only land blocks), earlier cutting will also facilitate a third cut in late August, further boosting total annual silage production.

Table 1: Guideline grass silage DMD for different classes of dairy stock

 Dry cowsSpring cows in milkGrowing heifersWinter cows in milk
DMD % 68-70 72 72 75
Typical first cut date Early June (or second cut) Late May Late May Mid May
First-cut yield (t DM/ha) 5.5-6.0 5.0-5.5 5.0-5.5 5.0*
*Assuming grazed in late autumn, not spring

It is often argued that spring-calving, pasture-focussed systems feed silage mostly to dry cows, and therefore do not require significant stocks of quality feed. However, spring-calving dairy herds need about 0.8t DM of 68-70 DMD silage per cow with 100% of the remainder as high quality (72+). Therefore, when factoring in youngstock, at least 50% of total silage will need to be high quality in a typical spring-calving system. This will increase for farms at higher stocking rates, or farms operating on heavy land.

Grass growth stage at harvest is the most important factor deciding silage quality. Once seed heads appear, DMD will be around 70% at most, and will drop by 1 point every 2-3 days after that. Lodged crops with dead material at the base will have 3-4% lower DMD still. Therefore the advice to improve average quality is cutting from mid-late May rather than into mid-June. Some flexibility in harvest date (4-5 days) is usually necessary to ensure favourable cutting conditions. It is advisable to monitor the development of your crop and see if the heading date, the absence of lodging and the absence of the accumulation of dead herbage, etc., are progressing as expected.

A common reason for putting off cutting silage is concern about nitrogen. A useful guide for fertiliser N is that grass uses 2.5 kg N (2.0 units) per day on average, so final N should be applied approximately 50 days before planned cutting date. If weather conditions are suitable for cutting, test the grass crop for sugars rather than sticking rigidly to the ‘2-unit rule’; the crop can be safely harvested sooner depending on conditions.

High sugar content allows the crop to ferment quickly in the pit/bale, reducing pH and preserving the crop correctly. Teagasc advisory offer a testing service (nitrates also), or indeed crops can be home-tested using a refractometer. If sugars are over 3%, then the crop will ensile readily, at 2-3% wilting rapidly for 24-36hrs will be beneficial (target 28-30% DM), while below 2% an additive will be required. Optimum mowing time is in the late afternoon/evening when sugars are highest, where this isn’t possible ensure mowing takes place after the dew has risen as this means that 2.5 tonnes water/ha (one tonne/acre) has been removed.

Some farmers consistently make good quality silage. Their repeated success does not indicate ‘good fortune’. They have a plan that works. It is essential to adhere to all components of a plan for successfully producing silage on your farm.

Also read: Completing a simple winter feed budget for a dairy herd