Making high-quality silage is critical in reducing winter costs on farms, irrespective of whether they operate a store or finishing system.

High-quality forage that is balanced with good yields gives the farmer more options. On the other hand, poor-quality silage means a higher meal bill.

All of the farms have now completed harvesting second-cut silage. While it is too early to analyse the feed value of second-cut silage, this week we detail the results from first-cut silage on the 10 farms.

Results

As a group the results make good reading, with a D-value averaging 73%, although they range from 65.6% to 76.4%.

D-value measures the digestible organic matter within the dry matter of silage and it will decrease progressively as the forage matures.

Basically the higher D-value, then the more digestible the grass and greater availability of nutrients. D-value is a good measure of overall nutritive value.

As shown in Table 1, there is also a relationship between D-value and cutting date.

Mark Lewis had the highest D-value within the group at 76.43%.

Ultimately, making high-quality silage starts long before harvest

Not only was his grass cut at the optimum stage before seed heads appeared, it was ensiled in excellent conditions after a short 24-hour wilt.

Ultimately, making high-quality silage starts long before harvest. Mark finishes store lambs off-grass during winter, with animals sold by mid-January. Silage swards were grazed bare.

Early applications of slurry, urea and CAN, along with mild weather, meant there was high-quality regrowth on silage ground.

In contrast, Ryan McDowell also harvested silage during good conditions in May, but D-value is lower than expected.

This silage will be retested. Given that grass on the farm is baled, the initial test results are possibly due to a poor sample.

Silage costs

The cost of making silage varies from farm to farm, primarily down to P and K status of soils. If phosphorus (P) requirement can be met by organic material, money can be saved using zero-P fertilisers.

Whether you aim for high D-value early silage or lower-value late-cut silage, the cost of growing the grass is the same.

Delaying harvest will increase yield and therefore reduce harvesting cost per tonne of fresh weight when grass is put in a pit

The majority of farmers will apply approximately 100 units/ac of nitrogen irrespective of planned cutting date.

Delaying harvest will increase yield and therefore reduce harvesting cost per tonne of fresh weight when grass is put in a pit.

However, the true cost of harvesting silage should be based on unit of energy.

For example, take a high ME silage crop (silage A), ensiled at 34% DM, and with an ME of 12.2. For every one tonne of fresh weight (FW) there is 4,148 MJ of ME.

A second silage (silage B) has a much lower ME of 9.5 MJ. Assuming it is also ensiled at 34% DM, it means there are 3,230 MJ of ME per tonne of FW.

Both silages cost £65/ac to harvest. If silage A yields 8t/ac FW, it produces 33,200 MJ ME/ac (4148*8t). Silage B yielding 10t FW produces 32,300 MJ ME/ac (3230*10).

Therefore, per unit of energy harvested, silage A (£65/33.2=£1.96) is cheaper than silage B (£65/32.3=£2.01).

Research

Recent work with beef cattle in Ireland reported that every percentage increase in D-value increased daily carcase gain by 23g.

Consequently a 5% increase in D-value increased carcase gain by 115g/day.

This equates to an extra 17kg of carcase weight over a standard 150-day finishing period. At £3.30/kg, that is an additional £56/carcase.

This comparison is based on concentrates fed at the same level of 52% of total dry matter intake.

Other factors

Wilting is beneficial to silage quality and a rapid wilt 24 hours before ensiling is ideal. Wilting to dry matters above 30% can cause fermentation problems.

Barry Carty has one of the highest silage dry matters analysed, but as all silage is baled on-farm, this should not cause any issues.

Wilting beyond 24 hours can actually reduce digestibility. Although Alastair McNeilly’s silage D-value is good at 73.16, it could have been higher.

Alastair mowed grass in good conditions but unexpected rain arrived. Grass remained on the ground for three days before lifting and D-value would have decreased during this time.

Sward type affects digestibility. Swards with higher percentages of ryegrass are more responsive to fertiliser and produce higher sugars.

However, across the group there is a range of established swards from one year old to over 10 years old.

Work in Ireland has also found little difference in D-value between old and new pastures that receive the same nutrients and are harvested at the same time, so long as each sward has at least 50% ryegrass.

Excessive N applications will actually reduce silage D-value. Most, if not all of the programme farms, aim for applications of 80 to 100 units/ac of N for first and second-cut silage respectively. Applying higher N levels offers no benefit.

Take home messages

  • Plan ahead: Removing excess herbage from silage fields before spring growth will reduce the amount of decaying material harvested in a first cut. However, overgrazing in early spring may reduce initial rates of growth.
  • Nutrients: When planning for silage, the correct level of nutrients must be applied early. If applying 100 units/ac of N, as a rule of thumb allow seven weeks for this to be utilised by grass. Meet P and K requirements according to soil analysis.
  • Cutting date: Feed quality will fall with delayed harvesting. Beyond early June, silages will generally fall below 70 D-value. Be prepared to harvest when conditions are suitable. Mow grass after midday and allow for a rapid 24-hour wilt, if possible.
  • Sward quality: Ryegrass content within a silage sward will generally decline with age. If ryegrass content falls below 50%, considering stitching in grass seed after the second cut is removed. Use a zero-N fertiliser and graze regularly to reduce competition from the existing sward, or apply a light coat of slurry.
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