Dry silage can last longer this winter

Increased grass growth during August has helped to replenish winter fodder reserves across much of NI.

But there are still areas of the country where fodder reserves are tight, and livestock farmers are hoping that a late cut of silage will help to alleviate the pressure on winter feed.

When assessing fodder stocks, many farmers have remarked that yields were lower this year and that silage pits are not as full.

While dry conditions did hinder grass growth during June and July, it should also be remembered that there has been a lot of good-quality silage made in near ideal conditions.

Therefore, grass silage harvested during these months will have a high dry matter (DM) content, and drier silage will naturally have less bulk, as there is less water present.

So while the pit of silage may look smaller than in previous years, there might actually be sufficient forage available when feed budgeting calculations are being done. Normally these budgets are done on a freshweight basis, but perhaps this is the year to do the calculations based on actual DM.

With average- to good-quality silage that has a higher DM this year, cattle will have a lower daily fodder requirement, meaning that the silage stocks can be stretched if cattle are fed to meet nutritional demand, rather than fed to appetite.

Consistent feed

The DM content is the amount of feed available after water has been removed. It is the DM content of any feed that contains all the nutrients and energy.

To compare the relative feed value of one feed to another, they are compared on a DM basis, ie after water has been removed.

This allows consistent analysis, regardless of whether you are comparing wet forages with a dry purchased ration.

Lower requirement

Silage typically has a DM content of 25% to 30% when grass is harvested under dry conditions in summer. This year, silage made during June and July will more likely be at least 30% to 35% DM.

Assuming that the feed value of forage is similar to previous years, cattle will require lower quantities of higher DM silage to meet their nutritional demand.

Therefore, it is important to get silage analysed in the coming weeks and work out what quantities of silage each livestock group requires.

Feed value

While DM is important, so too is the feed value of silage. Feeding good-quality silage with a D-value of 70% or above also means that cattle require less silage to meet their nutritional demand each day.

Again, this can lead to considerable fodder savings during the winter period on farms where silage stocks are under pressure.

Perennial ryegrass harvested before grass started to head-out in June, should have a high feed value this year.

Cattle demand

As a rule of thumb, cattle will eat around 2% of their bodyweight as DM every day. This means a 500kg store animal will consume around 10kg DM/day.

Assuming the animal is fed a forage only diet of good-quality silage at 35% DM, the animal would consume approximately 29kg of fresh silage on an ad-lib basis.

For silage with the same feed value but 25% DM, the animal will eat approximately 40kg/day of fresh material on an ad-lib basis, so logically, a pit of very dry silage will stretch longer.

For a group of 40 steers over a 100-day store period, the difference between eating 25% or 35% DM silage works out at 44t, worth £1,320 if silage is valued at £30/t.

Of course, there are other factors to consider when working out how long feed will last this winter.

For example, the stage of lactation for cows will affect forage demand, as will the level of supplementary concentrates being offered.

For dry spring-calving cows in good body condition when housed this autumn, the farmers involved in the BETTER Farm NI programme have managed to restrict these animals to 20-25kg/day of fresh silage in mid-gestation.

The main point of action to note is to get silage analysed so that cattle (particularly dry suckler cows) are not being overfed on higher DM silage.

Impact of silage dry matter

The effects of higher DM on silage volume is outlined in the following example.

Calculations are based on a silage clamp measuring 25m long by 12m wide, with an average clamp height of 2m.

As the example shows, with increasing silage DM there is an increased volume of DM feed available.

So while the physical yields of silage harvested this year have been lower than other years, there may well be a similar quantity of DM feed available from forage.

Calculating silage stocks

To calculate how much silage is in store, measure the length and width of the pit in metres and multiply by the average height of the clamp to work out the volume of grass present.

The next step is to convert this cubic volume to a fresh-weight tonnage. At 25% DM, multiply the cubic volume of grass by 0.68 to calculate the tonnage.

If the silage is 30% DM, multiply the cubic volume of the pit by 0.60 to calculate the fresh-weight volume and then convert to DM tonnage by multiplying by 30%. For 35% DM silage, multiply by the cubic volume of the pit by 0.53 to get the fresh-weight tonnage, and then multiply by 35% to get the DM tonnage. When you have calculated how much silage is in the pit in terms of DM, you can quickly work out how much you need to feed livestock either on a daily, weekly or monthly basis. This will indicate how long silage reserves are likely to last this winter and whether you need to stretch fodder reserves by feeding more concentrate or purchase additional silage.

How much silage is required?

To get a good indication of how much silage is required this winter, and how this compares with stocks, calculations should be based on typical intakes of silage DM/head/day.

Assume the following daily DM intakes for the various groups of stock:

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