The art and science of making supplementary feed was the topic of the second in a series of three webinars run by B+LNZ's Central Otago Farming for Profit committee.
Dr Jakob Kleinmans, a forage and nutrition consultant from NutriAssist Ltd, was the subject matter expert. He set the scene by outlining how important high-quality silage is for filling feed gaps and driving animal performance. Conversely, poor-quality silage costs money through greater wastage and lower intake.
What determines good silage
Jakob listed harvest timing, compaction and sealing, fermentation, and animal performance as the key determinants of good silage.
Harvest timing
He said harvest timing is a trade-off between yield and quality. As yield goes up, so does the quantity of Neutral Detergent Fibre (NDF), meaning the plants become more ‘woody’. The higher the NDF, the lower the intake, and the lower the ME and crude protein. Growing and lactating animals in particular need higher levels of ME and protein, so to maximise these, grass silage should be cut while the pasture is still leafy.
With cereal silage, the grain development adds energy (ME) but grain should not become too hard because it will pass through the animal. Ideally, cereal silage should be cut when the grain is at the cheesy dough stage, with the crop not drier than 45% drymatter. Below 28% drymatter, the crop is too wet; above 45%, it is too dry and harder to compact in the stack.
Drymatter matters
Conditions are ideal for fermentation at 30–40% drymatter. Below 28%, the silage stack will produce effluent. Above 40–45%, the silage will be too dry – compaction will be poor and the stack could generate heat and mould.
To estimate drymatter, Jakob recommends taking a handful of chopped or well-mixed plant material, squeezing it into a tight ball for five to ten seconds, and observing what happens:
- Ball forms easily and juice is released easily – drymatter is below 25%, too wet for harvesting.
- Ball forms but breaks apart easily, with no juice – drymatter is between 30–40%, ideal for harvest.
- Material barely sticks together and feels dry and springy – drymatter is above 40–45%, too dry for compaction.
A more accurate alternative is to weigh a sample of material and microwave it stepwise until it dries down to a constant weight - this gives the percentage of drymatter in the crop. A detailed method description is available on request.
Fermentation
The three factors that control fermentation are lack of air, sugar, and drymatter.
If a silage stack is airtight, it can last for many years. Once air enters, yeast could become active, temperature rises, mould develops, energy is lost, and intake drops.
Compaction is the cheapest insurance in a silage stack. Jakob suggests building the stack in thin layers of 15cm, using heavy tractors or loaders to continually compact it to a target density of 230kg DM/m³, and sealing immediately.
He acknowledges compaction isn't easy to measure, but as a rough guide: standing in front of the stack, if a person can get their fingers into it, it's too loose. Ideally, they should only be able to get their fingertips into the front of the stack.
For fermentation to occur, there needs to be sufficient sugar in the crop. Ryegrass is naturally high in sugar; lucerne and clover are not. These legumes need to be wilted sufficiently to allow sugar levels to rise before being made into silage or baleage.
Spoilage and feeding out
Spoilage is caused by oxygen penetrating the front layers of the silage, causing CO₂ to flow out the bottom of the stack. Ideally, the feeding-out rate should be greater than the rate of air penetration - i.e. 1–2m per week.
Baleage
Bales should contain 180–220kg DM/m³. Jakob recommends contractors use maximum pressure in the baler chamber and wrap bales with stretch film ideally within two to six hours.
Clostridia
Clostridial spores are the villains of silage fermentation. They occur naturally in soil and favour wet conditions. They can be incorporated into silage when the mower bar is set too low, when raking wet crops, when the stack is built on muddy soil, or when the field is flooded before harvest.
Silage should have a pH of around 4.5, indicating a healthy level of lactic acid. When clostridia spores develop in the silage, the pH rises and the silage takes on a foul, vomit-like smell.
Mould
Visible mould is never acceptable in silage. Mycotoxins may still be present if infection occurred before the crop was harvested. Mould almost always indicates oxygen ingress resulting from poor sealing, damaged bale wrap, inadequate density, or a slow feeding-out rate. All visible mould should be removed and discarded.
Silage analysis
Jakob describes silage analysis as a management tool, not just a lab report. Measuring ME, crude protein, NDF, pH, ammonia, and butyric acid indicates:
- ME – animal performance.
- Crude protein – protein supply.
- NDF – intake potential.
- pH – fermentation success.
- Ammonia – protein breakdown.
- Butyric acid – clostridia risk.
The results indicate what class of livestock the silage is suitable for.
Better silage begins before harvest
Good silage is the result of many things done well. Jakob recommends documenting every stage from harvest through to opening the stack. A monitoring form is available on request.