Grass silage makes up around a quarter of the annual feed budget on the average dairy farm. It is essential then, to have a plan in place to avoid deficits both in bulk and feed value. What happens on farms over the next few weeks will have a significant impact on silage stocks on dairy farms for next winter.
A good management plan will deliver on the three main objectives for quality silage:
• Good dry matter (DM) yield for the first and subsequent silage cuts with high annual grass tonnage per hectare.
• A clean, well-preserved silage with good palatability and minimal waste.
• The appropriate quality (DMD) for the type of stock to be fed.
Optimum DMD will vary depending on the type of animals to be fed e.g. dry cows vs. milking cows. Table 1 outlines typical quality targets and corresponding expected DM yields for first cut silage crops. Differences in yield due to cutting date will generally be offset by heavier second cut crops on swards cut earlier for first cut.
A good measure of whether you made enough silage last year is how much silage you have left over this spring. Before sitting down to complete your fodder budget consider if there will there be more stock on-farm compared to last year, will you end up cutting less area than last year and what is your fertiliser strategy for silage crops this year?
To estimate your fodder demand for next winter fill in your stock numbers and the expected length of the winter in months (including a 4–6 week reserve) in Table 2. Once you have estimated the silage demand (from Table 2) for the winter you can estimate the expected total yield from the area closed for silage. Multiply the total area (ha) closed by the expected yield per ha from Table 1.
Take into account the silage reserves remaining on the farm. Measure the length, width and height of the pit in metres; multiply the length x width x height and then divide by 1.35 to get the tonnes of silage (fresh weight). Multiply this figure by the dry matter of the silage - which you will find on your silage test report – to get the tonnes of silage remaining on a dry matter basis. A typical round bale contains 220 kg of silage on a dry matter basis.
There is a simple template available to complete the above calculations on PastureBase Ireland (www.pbi.ie). Having the numbers done early will result in better decisions made! A rolling reserve of one months feed above normal winter feed requirements should be in place to cope with adverse weather.
Grass DM yield is the single most important factor determining silage cost per tonne, but quality also needs to be considered when setting the target cutting date. The potential benefits from improving the DMD of first cut silage by three to four points for spring-calving herds of include shorter dry periods to replenish BCS, reduced concentrate supplementation for milking cows in late autumn, and improved growth rates in dairy weanling heifers. There are a number of key points to remember when planning a strategy that balances silage yield and quality.
Later cutting may be planned on some farms this year to bulk up yield. However, it is important to understand that while delaying the first cut well beyond (more than one week) grass heading date appears to put bulk in the pit, losses in digestibility means that total feed available to the animal is not increasing, or perhaps even declining. It also slows grass recovery rate and reduces second-cut yield, so that total yield of digestible feed per hectare is lower. Identify how much high DMD silage is needed for the system. Calculate the minimum area (1st and subsequent cuts) needed to produce this silage. Set a target cutting date. Use all remaining silage area to produce standard quality material. For spring calving herds, an option may be to take out a percentage of first cut as bales seven to ten days early to secure the higher DMD silage requirements of the farm.
With fertiliser costs much higher this year, farmers will be trying to make savings. However, silage ground must be fertilised properly. Silage ground should have received 2,500 – 3,000 gal/ac which should supply 25 kg N/ha or 20 units/ac and all the P and K requirements. For first cut silage the remainder 60-75 kg N/ha (48 – 60 units/ac) should be supplied from chemical N, a total N application of no more than 100 kg N/ha (80 units/acre) - including 12-15 units of sulphur - for a crop growing from early April to late May (60 days).
The grass growth stage at harvest is the most important factor determining silage quality. Once seed heads appear DMD will be around 70% at most and will drop by 1 point every 2-3 days after that. Well-managed silage swards closed from early April should have good yields of 5.5 to 6 t DM per ha (9-10 tonnes per acre fresh) ready for cutting by late May. A rule-of-thumb is that grass uses up two units of N (2.5 kg) per day. However, the crop may be harvested sooner depending on nitrate and sugar levels. Test the crop rather than delaying cutting based solely on the ‘2-unit rule’.
You may need to consider offloading non-productive or marginal stock to reduce silage demand for the winter. Selling poor performers, high SCC, lame or late calving cows has the potential to reduce any deficit or increase the reserve on farm.