1 Measure what’s left over
Measure how much silage is left over in pits and count how many round bales, if any, are being carried over to next winter.
To measure a pit, multiply the length by the width by the average height and then divide this figure by 1.35 to get tonnes of fresh weight.
This figure should then be multiplied by the dry matter of the silage, typically 24% dry matter (DM) to get the tonnes of dry matter available.
If measuring silage in a month’s time, make sure the pit is settled before measuring the height.
Each round bale of silage contains about 200kg DM of silage.
So between what is in the pit and what silage is in bales, you should be able to determine the starting point for what silage is in the yard.
2 Estimate what you need
Most spring-calving dairy farmers will bank on having 1.2t DM of silage in the yard for each cow carried over the winter. Liquid milk farmers and those on very wet farms with longer winters should be banking on 1.5t DM of silage per cow.
Over a four-month winter, weanlings will require 0.7t DM of silage while they will need 0.84t DM for a five-month winter.
Additionally, most dairy farmers will feed some silage to milking cows at the shoulders of the year. This should be budgeted separately to the main dry cow silage.
How much silage to be fed varies from farm to farm depending on stocking rate and soil type but is generally between one and two round bales of good-quality silage which is between 200kg and 400kg DM of silage.
For example, a farmer milking 100 cows in Laois and carrying 25 weanling replacement heifers over the winter will require 120t DM of silage for the cows and 18t DM of silage for the heifers.
This is presuming that cull cows are sold before winter and replaced by in-calf heifers.
If culls aren’t sold until spring, an additional 30t DM of silage will be needed.
In addition to the 138t DM of silage needed, an additional 100 bales of good quality silage will be needed if grass gets tight in the autumn, spring or summer, equivalent to 20t DM of silage.
3 Measure what’s growing
Counting chickens before they hatch isn’t a good strategy, but neither is burying your head in the sand. Yes, most farmers are at least a month away from harvesting silage but we should be able to know how much area will be cut and to estimate the yield. A good crop of first-cut silage will typically yield 6t DM/ha while second cut will yield 4t DM/ha.
If our Laois farmer has 19ha of silage ground and cuts it twice, that should bring in 190t DM of silage.
However, it’s crucial to remember that 20% to 30% of the grass growing in a silage field will not make it to the cow’s mouth. These losses occur at harvesting, ensiling and at feeding out. Good preservation and good pit face and feed face management can help to reduce losses but, on average, 25% of the crop is lost.
This isn’t all that unusual considering 20% utilisation losses is common for grazed grass.
A typical crop of first cut silage will yield 4.8t/ha DM of utilisable silage while a second-cut crop will yield 3.2t/ha DM of utilisable silage
So, in reality, the 190t DM of silage growing in the field will only be 143t DM of silage that the cows actually consume.
In other words, a typical crop of first cut silage will yield 4.8t/ha DM of utilisable silage while a second-cut crop will yield 3.2t/ha DM of utilisable silage.
Remember that the above is based on typical yields. If less fertiliser (nitrogen and compounds) has been applied to silage ground this year, then lower yields can be expected.
As a general rule of thumb, 100kg N/ha (80 units N/acre) will grow about half of the total yield.
So, if a farmer only spreads half of what is normally spread for silage then we can expect silage yields to be back by 25%.
Increasing the area available for silage is another false economy
Delaying harvest by say two or three weeks will be a false economy as the quality will drop significantly and second cut yields will also be much lower. Therefore, if 50% of the normal amount of nitrogen was applied to silage ground this year, farmers can expect first-cut silage yields in the order of 3.6t/ha DM of utilisable silage.
If our example farmer applied half rate of nitrogen to his silage ground, rather than having 143t DM of silage available for consumption, he would be back to 114t DM of utilisable silage meaning each cow would only have 0.9t DM of silage available to them rather than 1.2t DM.
Increasing the area available for silage is another false economy as this will increase harvesting costs and mean less land is available for grazing.
Compare how much silage is required for the winter with how much silage is likely to be made and how much is carried forward.
If the budget is showing that there will be less silage than required then action needs to be taken.
The following is a list of steps farmers can take to ensure they will have enough forage for next winter: