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Silage Making Targets

by Ranald Fowler

Dairy farmers, sheep farmers and beef finishers have much to gain through increased profitability by planning to make their silage with a D value of 70 -75 (ME 11.5 -12) and a DM of 28-30%. To do so requires positive forward planning, so that the contractor, if used, will be on the farm the day after the first small part of a seed head is detected in the growing crop.

Thereafter the D value and ME drops so rapidly, that a weeks delay in cutting will necessitate feeding an additional 2.2 kg of concentrates /cow/day to achieve the same milk yield! And that increases with each weeks delay. To catch the right starting day means walking the silage fields twice a week, having your contractor pre-warned and being fully prepared for action; with pits all cleaned, silage sheets and inoculants on farm.

More from your investment

Although some of the management steps will have already been taken, it is probably worth restating that perennial ryegrass swards give the greatest response to fertiliser applications and a more consistent silage quality. If replacing leys at any time it is worth choosing a new ley mix in which the varieties all head within a week’s spread of indicated heading dates. This enables a higher yield and quality when cut on the right date, as yield gain is largest pre-heading, after which the seed heads elongates and becomes more fibrous, no new leaves are formed and existing ones start to die off. Leys with low perennial ryegrass content will have 3 to 5 units D, lower than ryegrass at the same stage.

Crop growth is fastest and most responsive to fertilisers in May and June, so to make  sufficient high feed value silage it is best to remove the first cut by mid May and re-fertilise immediately for a second cut 6-7 weeks later, making full use of the seasonal rapid growth. Remember every days delay in fertilising the aftermath causes an irrecoverable yield reduction (Kingshay trials) Spread 80u N/acre along with 45-50u K2O to replace the potash removed and maintain the vigour of the perennial ryegrass. If the soil index drops below 2 then the perennial ryegrass starts to die out of the sward: a costly loss!

Grazing pre-first cut until early April, cuts yield by the same Dry Matter as that removed by the grazing, but also removes any over wintered, decayed herbage and will improve the quality of the cut by 3-4 units D.

Early harvesting

Cutting crops at a leafy stage provides a much more nutritious and highly digestible silage that improves intakes and thus milk yield, but also improves milk protein.  Preferably start cutting after midday when all dew or rain has dried off and grass sugars are at their highest. Do not cut below 5-6 cms or grass recovery will be delayed. Below this height the material is of lower feed value, but guards the growing tip and supplies the necessary sugars that push up the new leaves. In addition to cutting at the correct stage of maturity, there are two further steps that should be taken to lift milk yields and quality, or improve beef growth rates. These are, rapidly wilting the crop and using an effective inoculant.


Rapid wilting, means tedding out the crop within an hour of cutting to get a 10% drop in dry matter within 24 hours. This has been shown to improve both milk butter fat and especially milk protein.

Other advantage of a rapid wilt are:-

Enables a faster pick up and fewer loads; as, for every 1000 tonnes of grass cut at 18% moisture and wilted to 28%, 350 less tonnes of water will have to be carried.

There will be less or no effluent produced.

More silage dry matter can be stored in existing pits.

Test the DM by wringing some representative samples with the hands and if moisture can be wrung out, then the moisture content will be below 25%.


Proven inoculants work by ensuring a rapid reduction in the pH of the grass ensiled. In turn, this reduces the breakdown of water soluble carbohydrates, protein and digestible fibre, maximising the feed value of the silage. While many feed trials have shown yield increases of 0 to 2lit/cow /day, the early trials at Hillsborough indicated a 0.18% increase in butterfat when used on early cut grass, as a result of preserving the digestible fibre.

Chop length

Chopping grass allows the sap to flow, releasing sugars to aid fermentation in drier silages, but also enables effluent to run more readily in wetter silages, removing up to 10% of their nutrient value. Chopping enables easier consolidation and the exclusion of trapped air, again benefiting fermentation.  The promoted recommendations are that, if crop DM is greater than 20%, the chop length should be 10 -25 cms; while for grass of under 20% DM the chop length should be 20 to 40cms. However, too short a chop reduces the amount of long fibre available for efficient rumen function.

By contrast, on the continent where most grass silage is picked up with forage wagons, high dry matters of over 30% and long chopping of 150-200cms are the norm. The difference may be that their clamps, generally without walls, are completed daily, sealed and weighed down until feeding out; where as we take 2 to 3 days to fill, sheet down and finally seal. 

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