Grass silage usually forms the basis of ewe diets in the final weeks prior to lambing.
However, few sheep farmers will know the actual feed value of the forage offered to heavily pregnant ewes.
The mild autumn helped build grass covers and in most cases, farmers report ewes in strong body condition heading into the new year.
Where ewes are carrying slightly more flesh than desired, it is important that body condition is altered in the runup to lambing.
This is another reason for knowing the feed value of silage. Silage with a higher feed value will see ewes in good flesh maintaining condition and leading to more problems at lambing time.
Silage quality will vary due to the stage of maturity when grass was cut, weather conditions during harvesting, whether grass was wilted to increase dry matter and how well forages are preserved.
Given the increase in concentrate costs, up £50 to £70/t (€60 to €83/t) year on year, there are considerable financial savings to be made from getting silage analysed for feed value.
In some cases with high-quality silage, supplementary concentrates may not be required until the final two to three weeks pre-lambing.
At the opposite end of the spectrum, with lower quality forage, twin- and triplet-bearing ewes may need supplementary feed offered earlier than normal.
Ewes that are offered a balanced diet pre-lambing will experience fewer problems post-lambing.
Colostrum quality and milking yield are also improved in early lactation, helping to reduce mortality in the first few days of lambs being born.
It should be emphasised that a silage analysis is only as good as the sample taken. Concentrating on silage from one or two areas at the pit face will not give a representative reading.
Silage should be taken from multiple points on the clamp, thoroughly mixed together and then a final sample taken for analysis.
Equally, it is worth taking a follow-up sample once you reach the halfway point in the clamp or bales to see if diets need tweaking.
All of the farmers have now had silage analysed and this information is being used to draw up winter feeding plans.
While there are still March- and April-lambing ewes on a grazing only diet, some of the farmers have moved to begin housing early lambing ewes and ewe lambs.
The results of a silage analysis can be off-putting as there are multiple readings presented such as dry matter, pH, crude protein, metabolisable energy (ME) and D value. A brief explanation of what these parameters mean is outlined as follows.
Dry matter (DM)
This is the amount of silage remaining once water has been removed and expressed as a percentage. A good target for grass silage is a dry matter between 30% and 35%.
The lower the figure, the wetter the silage and vice versa. Silage that is too wet, or too dry, will have a negative impact on animal intakes as well as preservation.
Silage pH gives an indication of how well the forage has been fermented. Ideally, a well-fermented grass silage will have a reading around pH 4.
At this level, silage is less likely to spoil, or heat, once the clamp has been opened and forage is being fed out.
However, higher dry matter silages are likely to have a pH ranging between 4.5 and 5, yet still have a stable fermentation.
Crude protein (CP)
Protein is a key part of the ruminant diet and drives weight gain and milk production in animals.
In terms of grass silage, the crude protein value generally reflects the quality of grass sward harvested. Fertiliser applied to swards can also affect protein levels.
Silage swards harvested before seed heads develop tend to have higher protein levels compared to swards harvested with a high percentage of stem and seed heads present.
Most first-cut grass silages harvested in late May to mid-June usually have a crude protein level between 12% and 15%.
Swards that headed out will have lower protein readings which means a greater reliance on supplementary concentrate is required.
Metabolisable energy (ME)
ME refers to the energy content that silage will provide in the animal’s diet. Again, silage swards harvested with a high leaf content will have a higher ME and vice versa.
Silages with an ME between 11.5 and 12 Mj/kg DM will require lower levels of supplementary concentrate as these forages are high in energy.
Silage with a high level of stem and seed head present will have much lower energy levels and require higher levels of supplementary concentrate.
DMD or D-value
The DMD or D-value is a good one-stop, overall indicator of silage quality. The more technical explanation is that DMD is the percentage of digestible energy within the dry matter content.
Basically, the higher the DMD%, the higher the feed value of the forage. It will also be more digestible, so animals will eat more and performance will be higher. As a rule of thumb, a DMD of 70% or higher reflects good-quality silage, with average-quality forage around 65% to 66%.
Silage with a high level of ammonia is more likely to have had a poor fermentation. As a result, there will be a high level of spoilage once bales or the clamp are opened.
Silage is also likely to have a foul smell, have a brownish/black colour and will quickly heat once fed out.
A high ammonia reading is usually the result of grass being harvested before residual nitrogen has been fully utilised by the sward, or when leafy grass is cut in wet conditions and not wilted to increase sugar concentration.
A good target is to have ammonia levels between 5% and 10%. A forage with ammonia levels above 10% will be more prone to spoilage, heating when fed out, and animal intakes will be low.
Neutral detergent fibre (NDF)
Silage with a high fibre is harder to digest. This means intakes are lower, which ultimately reduces performance.
Silage harvested with a high percentage of leaf will be easily digested and such forages tend to have an NDF between 45% and 50%. As readings increase beyond 50%, fibre content increases.
Silage is made in bale form on five of the programme farms. First-cut silage will be fed to ewes on seven farms in the coming weeks.
Dry matter (DM) content ranges from a low of 19% to a high of 50.3% for bales of second-cut made on Trevor Nixon’s farm.
The higher dry matter content of this fodder is a key factor behind the pH reading at 5.0. However, bales should be well fermented as ammonia levels are at 7%.
While silage on James McCay’s farm has a low-DM silage after harvesting in damp conditions, it still has a relatively good feed value in terms of energy and protein and should help to limit concentrate requirement in the run up to lambing.
First-cut silage made on Dermot McAleese’s farm had the highest D-value at 75.8% reflecting grass harvested before standing swards started heading out in June.
Dermot has also undertaken a reseeding programme on farm and there are some younger swards being harvested for silage.
Closer analysis shows the first cut on Dermot’s farm has an excellent energy (ME) value of 12.1 Mj/kg DM and is also high in protein at 14.7%.
At the outlined feed values, this silage should be able to meet the nutritional demands of ewes in optimum body condition and carrying single lambs.
For twin-bearing ewes in optimum body condition and offered this silage when housed, supplementary concentrates are unlikely to be required until the final fortnight prior to lambing.
Monitoring body condition
Dermot’s silage also has a low fibre content at 45% NDF. This means it will be easily digested and ewe intakes will be higher if silage is offered on an ad-lib basis.
Therefore, Dermot will need to handle ewes regularly, as there is potential for animals to gain body condition, especially in the case of ewes carrying single lambs.
Regular handling will enable Dermot to restrict silage if necessary before it leads to potential problems at lambing time.
In the event of a delayed turnout to grass post-lambing, this silage should be capable of maintaining milk production without the need for concentrates.
On Tynan Abbey farm run by Kate Kingan and Peter Mant, a large amount of first-cut silage was harvested from surplus grass on the grazing block to maintain sward quality for lactating ewes.
By removing silage as bales, it provided greater flexibility in cutting dates for Kate and Peter compared to closing up ground for one large crop to be ensiled in a clamp.
Again, silage is benefiting from younger grass swards as well as improved grassland management.
At the outlined D-value of 70%, ME of 11.2 Mj/kg DM and a crude protein of 14.6%, first cut silage will require low levels of supplementary concentrate feeding this spring for twin bearing ewes.