“A cut corner here or a slight oversight there can ultimately result in silage which is unusable due to insufficient dry matter content, or worse, that is dangerous to herd health because of mould growth and the likely presence of mycotoxins orlisteria.
“Many farmers have come to accept some issues, particularly with mould, as inevitable and as a necessary evil. The reality, however, is it’s all too often caused by committing one of a number of cardinal sins.
“Mould growth, particularly in silage bales, depends on two crucial contributory factors. Firstly, the harvested forage needs to be contaminated with mould spores prior to it being baled and secondly air – or more specifically oxygen – needs to have entered the bale after wrapping.
“Oxygen will always be present in baled forage, but if a bale is wrapped correctly it will be quickly used up through respiration, either by the plant or by aerobic microorganisms present on the crop. Once it has been consumed, the wrap acts as an air barrier and will inhibit any further oxygen ingress.
“Moulds on the other hand are ubiquitous on farms and so it is impossible to completely remove all traces of contamination from the forage. That said, you still can, and should, take steps to minimise their numbers and to reduce the risk.”
Dr Davies says this starts with the grass itself, as any surplus grass at the end of the previous growing season must be removed completely, by grazing or topping.
If left unchecked this material just dies and provides nutrients to support the growth of moulds and other undesirable bacteria, which remains in the sward until harvest.
Removing this surplus grass helps reduce the number of mould propagules in the harvested sward. Surplus grass has also been shown to reduce spring grass growth rates and, thus, first cut grass yields.
Dr Davies says the need to remove surplus grass could be more pronounced this year, as the early snowfall last autumn and winter caught many farmers unaware and before they were able to properly prepare their fields.
This can also lead to silage being contaminated by moulds, says Dr Davies: “Sometimes harvesting over-mature grass is unavoidable because of the weather conditions, or because you require a mature low D value forage for feeding certain classes of stock, such as dry suckler cows, or if farmers are participating in environmental management schemes.
“This practice is, however, more often than not, carried out because farmers are looking to increase crop yield despite the trade off in forage quality.
“The problem with this is that as forage matures and the seed sets, the vegetative parts of the crop, like the stems and the leaves, begin to die and become increasingly vulnerable to invasion by fungal pathogens.
“These pathogens, which are not necessarily visible to the naked eye, will in turn enable many none pathogenic fungi to establish themselves in the forage, creating a high overall load of fungal propagules.”
In addition to risking increasing the silage’s mould population, harvesting over-mature grass with stalky stems can puncture bale wrap and allow air ingress. Therefore, if you are producing silage from this material, consider wrapping bales with eight layers of film.
If you want to reduce the likelihood of mould contamination within your silage, avoid leaving your cut grass in a thick narrow swath, says Dr Davies.
Such swathes encourage mould growth because their density results in higher temperatures and humidity levels, both of which enable bacteria to thrive. In addition, thick swathes reduce the wind’s effectiveness in helping to dry the crop out.
Aim to spread grass over 80-100 per cent of the original harvested area (depending on ground conditions) as soon as possible after mowing, and certainly within two hours.
Doing so will promote rapid wilting and enables the sun to play a more active role in mould control – in the same way as UV radiation causes sun burn and skin cancer, it is just as potent at killing undesirable bacteria and moulds in the swath.
This reduces the chance of damaging the wrap, preventing oxygen entering the bale and mould forming.
Dr Davies says: “Admittedly the advice has always been, and always will be, to wrap bales as quickly as possible – and wrapping in the field would appear to facilitate this.
“Doing so can present other hazards however. Dropping a well wrapped bale on to the recently cut sward presents the very real risk of the wrap being punctured by either stubble or by stones.
“When that wrapped bale is then picked up and moved to the stacking site, this damage can be exasperated.”
If bales are wrapped in the field, Dr Davies recommends checking bales carefully for damage from stubble.
“Any holes caused by stubble may be small but, rest assured, oxygen is much smaller,” he says.
It is recommended you move bales as quickly as possible after wrapping – ideally within two hours and certainly no more than eight.
Once at the storage site, the bales should be left in place until they are fed out.
“Many farmers understand moving a bale once fermentation is underway means a greater likelihood of damaging the wrap and opening up the seals between layers of film, enabling oxygen to enter,” he says, “As such, they leave them alone for two weeks. However, even
if you move them after this time, there is a significant risk of facilitating oxygen ingress.
“That’s because the bale is most likely moved with a bale grab, which in effect squeezes the bale as it’s picked up. This squeezing action forces the carbon dioxide in the bale out and creates a potential vacuum.
“Once the bale is placed in its new resting place and the grab is released, the bale returns to its original shape with the vacuum drawing in unwanted air and oxygen, which will ultimately feed mould growth.”
It is not okay to spike an unwrapped bale in order to move it to the wrapper, says Dr Davies.
“When you produce a bale, you’re creating a densely packed mass of forage where much of the oxygen has already been squeezed out.
Once you spike it though, you’re undoing all your hard work.
“Not only does the central spike hole allow oxygen back in but you’ll also create lots of concentric holes around this as you move the bale, all of them having the same negative effect.
“It’s a lot like ripples in a pond. Ultimately, this introduces so much oxygen that moulds are able to grow before the oxygen is used up after the bale has been wrapped. As for spiking a wrapped bale – that really is the ultimate sin.
“You’re deliberately puncturing a film and any patch used over the resulting hole will never provide the same degree of oxygen protection as the original undamaged film, irrespective of how well it is applied.
“It is always better to use a grab whenever you’re moving bales – wrapped or not.”
Birds and vermin do not care that your bale wrap is there to provide an air barrier – and it is not just wild animals you need to worry about either, as cats’ claws can have the same negative effect.
Do not squander the time, effort and energy spent creating baled silage by not placing a net over the bales.