UK milk production from grass forage is remaining stubbornly static, UK Technical Support Manager Roy Eastlake believes producers must challenge what they are trying to achieve with silage, especially grass.
“If the systems of forage production employed aren’t focused on producing a higher proportion of total production from forage, then you question those systems starting with the most fundamental question of all which is why do we use grass silage?”
The objective for all producers cutting grass is the same, which is to produce sufficient, high-quality forage to be a key ingredient in cost-effective diets, whether fed in isolation or in combination with other forages. This objective can then be broken down further.
Three optimisation factors
Any silage bunker can basically be viewed as an energy store, the better the quality of the silage, the higher the energy and the less the producer needs to rely on purchased feeds. Produce quality silage requires the optimisation of three factors. The first is the physical yield; we need to produce the quantity. The second is dry matter (DM) content as for effective diets we need silage ideally from 30 to 35% DM. Finally, we need a high metabolizable energy (ME) content to maximise the energy per kilo of dry matter.
Production from forage can only be maximised if all three of these areas are optimised. If we have silage that is too wet or too dry, then intakes will be compromised. If we don’t make enough, then intakes have to be restricted to ensure stocks last, meaning more purchased feeds are required. If energy content is reduced, then energy intakes are suppressed, again driving up purchased feed use.
By breaking down the reason for cutting, grass into these three elements, it is possible to focus on improvement and to develop a system which will increase the energy in the bunker in a form the cow can utilise.
All too often, however the quantity of grass produced that dominates producers decision making, with success defined by ‘having enough’ and ‘clamps full’ but this disregards the actual quality. As any crop matures you certainly get more bulk to satisfy the quantity requirement but quality declines. At peak, a grass plant will be around 12.8MJ/kgDM, but grass silage typically averages around 10.6 MJ in the UK, which is a major loss of nutrients.
Not only do mature heavy crops have lower energy, but they can also be harder to wilt, making it harder to hit the dry matter target. If the crop has to wilt longer to hit the dry matter target, then respiration losses can increase further contributing to energy loss.
For grass silage, utilising a system of more frequent, shorter interval cutting offers a change in thinking that can help balance the three objectives of yield, energy content and dry matter.
Grass offers a great opportunity to make better quality forage. It produces a high energy content in a highly digestible form, and it does it repeatedly. Producers using grazing systems have known this for years, and it is why they graze frequently, taking the crop off before energy starts to decline. When making silage, we tend to work against the crop rather than with the crop, letting quality decline to make big cuts of poorer quality, rather than more smaller cuts of a higher quality.
Cutting at 28-day intervals when the grass is at the flag leaf stage will give a cut crop at higher energy values, closer to a 12.0 MJ.
By operating a policy of silage in a day, only cutting what will be picked up the same day, respiration and field losses can be reduced to preserve energy. The risk of crop damage due to rainfall is also reduced with smaller cuts on the ground at any one time and more opportunity to time cutting to avoid poor weather.
More frequent cutting combined with leaving a decent stubble can then exploit the rapid growth potential of grass, allowing target total quantities required to be reached, albeit from more cuts but at higher energy levels.
Targets for grass silage
Total target forage intakes 12-14 kgDM/cow/day
Cutting interval 28 days
Stubble length >6cm
Sugars in fresh grass >10% in dry matter
Nitrates <1,000mg/kg dry matter
Target DM at ensiling 30 to 35%%
Target NDF at harvesting 38-40%
Target ME in silage >11.5MJ