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Target quality silage for sheep farms

Target quality silage for sheep farms

Damian Costello, Sheep Specialist, shares key advice to ensure you produce enough high-quality silage for your ewes next winter.

The inclement weather has presented many challenges to sheep farmers this spring, not least forcing a delay in fertiliser applications and the closing up of silage ground on many farms.

Where ewes are winter housed, silage feed value has been ranked as the third most important factor affecting profitability in mid-season sheep production (Keady and Hanrahan, 2006).

Like many things, making good silage is all about attention to detail right through the various stages of the process. You can’t make a silk purse out of a sow’s ear is an old saying that can apply to making high feed value silage.

Unless you are harvesting top-quality grass at the right growth stage that has been appropriately managed since pre-closing, you will not end up with top-quality silage. Dry matter digestibility (DMD) is the key factor influencing silage feed value and this article gives practical tips on providing enough high DMD (target 75%) silage for your ewe flock next winter.

How much silage do ewes require?

The guideline silage requirement for the average lowland ewe is 0.15 tons pit silage per ewe per month or 0.19 bales per ewe per month. Budget for 15 to 16 tons pit silage or 19 to 20 bales per 100 ewes per month.

Where rotational grazing is practised, some or all of the sheep silage requirement will be met from removing heavy grass covers as high-quality surplus bales. It is really important to clearly identify with permanent spray paint the different batches of bales. Ensure that bales likely to be high DMD material are stored so that they will be accessible when needed. The actual quality of the various batches should be determined later by analysing representative silage samples. Ideally ewes should be offered high feed value silage right throughout the housing period.

Management at closing

Graze out tightly to 4cm to remove any dead material prior to closing for silage. Roll ground where necessary to reduce the risk of soil contamination. If clods of soil end up in silage (pit or bale) there is a risk that sheep fed on this silage can ingest the bacteria that causes listeriosis.

Check phosphorous (P) and potassium (K) requirements based on most recent soil analysis, taking care in particular not to exceed P allowances. The normal recommendation is to apply up to 100 to 120kg/ha of nitrogen (N) in the form of an appropriate compound or protected urea, allowing that about 30% of N previously applied for grazing will still be available to the plant. However, this year, reducing chemical N applied at closing will enable earlier harvesting and reduce the risk of crop lodging pre-harvest, which negatively impacts digestibility. If for example 80kg/ha of N is applied in late April, this nitrogen will be used up in 4 to 5 weeks, allowing for a late May / early June harvest date. This in turn allows for closing in time for a second cut where necessary.

Harvest at correct growth stage

The main factor affecting DMD is crop maturity at harvesting. The target for high-quality, first-cut silage is to be cutting before grass seed heads start to emerge. A common reason for delaying harvesting is concern over whether the crop has used up all applied N. If in doubt, contact your local Teagasc advisor to test grass sugar levels and nitrates – it may enable crop to be safely ensiled sooner given the right conditions.

Don’t delay harvesting for a prolonged period, as research has shown that for each week harvest is delayed digestibility goes down by 3% units per week (Keady et al, 2000). The aim is to harvest leafy material before grass heads out and before base of the sward begins to decay – regularly walk and inspect the crop, watch the weather and take the best available opportunity to mow around the planned harvest date.

Tips on mowing

The optimum time for mowing is in the afternoon of a sunny day when grass sugars and dry matter levels are at their highest. In reality, this is not always practical but at least aim for a dry day and allow the dew to evaporate from grass before mowing. Don’t mow too bare to avoid ensiling dead material and the risk of soil contamination. Ensure that mowers and tedding machines are set at the correct height to avoid rooting up soil. Where soil contamination may be an issue due to poor ground conditions at harvest, identify as silage not to be fed to ewes next winter.

Effect of wilting on silage quality

Wilting negatively impacts digestibility and the rate of reduction in DMD due to wilting has varied among different studies. Each day (24 hours) wilting will reduce silage DMD by between 0.5 and 2 percentage points. Therefore, aim for a rapid wilt of 24 to 36 hours after mowing. Target 25% dry matter at ensiling for pit silage and 30% dry matter for bales. Spreading heavier crops over the ground straight after mowing helps achieve this but is generally not necessary for light cuts. Surplus bales or light crops should be baled and wrapped relatively soon after cutting, particularly if good drying conditions prevail.

Anaerobic conditions for good preservation

Ensure silage pit is covered and fully sealed as soon as possible after filling. With bales, extra layers of plastic wrap combined with careful handling and storage will help ensure air is totally excluded from the bale. Don’t allow birds or other vermin damage your silage clamp or bales and don’t forget to repair any bales damaged in transit to avoid mould and wastage.