Delaying silage cutting date will have negative effects on silage quality & quantity for dairying

Grass silage makes up about a quarter of the annual feed budget on the average dairy farm. With below average growth rates in late April/early May, James Dunne, Dairy Specialist Ballyhaise, answers the common question: “should silage cutting date be delayed to allow first cut yields to increase?”

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 forage intake. With lower than average growth rates through the latter half of April and into early May, one commonly asked question is “should silage cutting date be delayed to allow first cut yields to increase? ” It is important to consider the yield of forage DM 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 towards mid-June.

Management decisions around first cut silage yield should be made on the basis of meeting DMD 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 harvested 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.

It is often argued that spring-calving pasture-focused 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 determining silage quality. Once seed heads appear, DMD will be around 70% at most, and will drop by 1% DMD every 2-3 days after that. Lodged crops with dead material at the base will be 3-4% lower DMD. Therefore the advice to improve average quality is to cut from mid-late May onwards rather than to defer cutting closer to 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 delaying silage harvesting is concern about Nitrogen content. 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 offers 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 24-36 hours 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 that 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 to successfully produce high quality silage on your farm.

You can check out more of what James has to say on 1st Cut Silage in today's DairyEdge podcast below

You might also like to read Plan a Safe Silage Season in 2021 

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The Teagasc Dairy Specialists issue an article on a topic of interest to dairy farmers every Monday here on Teagasc Daily