By Mikaela Baker (B. Ag Sci), TRAC Ruminant Productivity Consultant
Silage can be tricky to nail at the best of times. What makes great silage is multifactorial in the parameters we are chasing, such as dry matter, neither too high or too low; fibre fractions; energy content; sugars; a low pH and high silage acids, but in no scenarios do we want butyric acid.
This year we saw the challenge of either cutting early and accepting loss of quality from rain, or letting silage go a bit too long but hoping for better curing conditions – neither of which is what we hoped for. However, as with all things in farming there is a gamble and what makes us continue moving forward is the ability to re-plan, adapt and make the most out of a scenario. The best chance we have of achieving our desired results at the end for either milk production or weight gains, is having an understanding of what can go wrong and how, and then put in place mechanisms to use the silage in the most efficient way.
How does fermentation work in silages?
The difference between silage to hay and fresh cut grass, is that silage has high moisture and has gone through a fermentation process to allow long term storage while retaining many of the nutrients. To create the acids to preserve and retain the nutrients, the silage goes through several phases where acids, temperature and O2 levels change.
When the grass or crop is cut, the plant is still respiring and using up sugars and energy, the faster the stomata close the more nutritional value is retained, this is where conditioning and tedding facilitates this process. When the forage is layered into the pit, the most crucial component is reducing the amount of oxygen throughout the forage.
Phase one is the aerobic phase, this begins immediately after cutting and early on after being ensiled. This is where respiration and proteolysis occur. During respiration, sugars and O2 get converted carbon dioxide, water and energy for the microbes. This will continue as long as substrate and oxygen are available. When looking at time on the ground it is estimated that there will be 5% nutrient loss per day - so it is a high priority to shorten this phase. In this phase, the sugars are used for aerobic bacteria causing oxygen to drop in a closed stack. The other main factor in this phase is that we will see a rapid increase in temperature. If the temperature goes too high there will be more nutrients used and result in an increase in NDF, ADF and drop in energy for lactation – the increase in fibre as a percentage is because we are losing other components. Overheating can also lead to degradation of protein quality where we see high levels of soluble protein and it can also increase undesirable bacteria, yeasts and moulds. Proteolysis is the second portion of phase one, where we can see protein breakdown resulting in high levels of ammonia (also from excess O2) or high temperature. The longer the silage is exposed to air, the greater protein loss will be observed.
What causes higher temperature?
Too much oxygen from a poorly compressed stack
High dry matter (>50%)
Poor spreading over stack – uneven compressing
Long paddock time
Phase two will start when all of the oxygen has been used and we begin fermentation. Acetic acid will begin to be formed and pH will start to decline, however there is only weak acids at this point and high nutrient losses can be observed. This phase should typically only take 1-3 days. An important time to consider regarding relocating baled silage, by moving the silage we will be again adding oxygen and the entire process will begin again, losing more nutrients. Toward the end of phase two, lactic acid will begin to be produced and pH will continue to drop towards 4. The higher the sugar content to begin with, the stronger the fermentation that can occur as this is food for the microorganisms.
The silage is now at stable state with a constant temperature and no more fermentation is taking place. Generally, we allow 6 weeks to reach this phase. It is only when oxygen is introduced back to the silage that fermentation can begin again - think of moving baled silage, accidental tears to the plastic and opening the face of the stack to feed out, all problems that can restart the process, however if the oxygen is not eliminated such as taping the holes, it will never reach phase two and continue to lose nutrients and grow mould.
There has been so much work that goes into making silage, it is important to maintain the integrity of the feed when we go to feed it out, such as face management or the time that either pit or baled silage is sitting in the paddock exposed to air. This is the ideal growth area for moulds, yeast, aerobic bacteria and risk significant dry matter loss and loss of nutritional quality – we can lose up to 50% of the nutritional value!
A few areas where we can preserve quality:
Move through 30 cm of silage face in a pit per day - Is the face too big? Feed off from left side one day, then from right side next day
Plan the size of the stack and minimum quantity that will be fed out per day
Remove silage from top to bottom – lifting a bucket upwards can lift portions of the stack and allow air to enter.
Remove evenly from top and bottom of face – dispose of wasted / loose forage appropriately
Only pull back plastic cover enough to remove 1 days feed
When feeding out bales – feed as close to the time the animals will consume feed
When it is warm or humid, consider the time it will take animals to consume the silage and the impact to mould growth.
What we can’t control: What happens when silage gets wet?
This will depend hugely on what stage the crop was, how soon after cutting the rain was, frequency and quantity of rainfall. What we do know (fairly certainly), is that rain significantly increases risk of mould – and mould can impact dry matter intake, fertility and growth rates. Fortunately, this we can control through toxin inhibitors in dairy rations and through loose lick minerals and dilution of feed If needed. The other things we aren’t so certain about, is which areas might be challenged from rained forage.
When there is rain or external water sources on the forage, it can increase the length of respiration and the plant uses its reserves of sugars and other soluble carbohydrates. This can also result in leaching of proteins, soluble carbohydrates, and some minerals. The challenging conditions can cause leaf shattering, loss of energy from respiration and microbial activity and an increase in fibre percentage.
Be sure to get a feed analysis before any purchases and for all home-grown forage, to plan for the year ahead and how to manage any unwanted surprises. Get a mould and yeast count before purchasing, or have one done prior to feeding.
Depending on where your count sits, there are ways we can often still utilise the feed:
Dilution is key – the risk will be reduced if the animals are eating less of the problem.
Do a risk assessment on the group you are choosing to feed, if they are rams being prepared for joining, joining animals or animals actively giving birth, choose a lower risk group.
If you need to feed the forage (or grain) and are concerned about the impacts or seeing clinical signs, there are mycotoxin inhibitors that can be fed with grain or with loose lick minerals.
A mould and yeast count will take 5-7 days from receival in Bendigo, however an identification will take up to four weeks. Take a sample as normal for a feed analysis preferably with a corer, place in a plastic zip loc bag clearly labelled and do not freeze. Post with your submission form via express post. For a nutritional analysis of silage, select the A1 Plus to receive silage acids.
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