Grass Sileage
It is impossible to produce high quality silage from low quality pasture, no matter how good the fermentation is. Both the quality of pasture and the quality of the fermentation must be considered.
What is pasture silage?
Silage is pickled pasture. When pasture is ensiled, its sugars are converted into lactic acid by bacteria. It is the lactic acid which pickles the pasture, allowing it to be preserved for a lot longer than it would have been if left in the open air. With well-preserved silage, losses in feeding value during fermentation will be small, and the final silage will be only slightly lower in feeding value than the original pasture.
Minimum values for high quality silage is 10MJME/kgDM and 16% crude protein.
Good quality pasture silage is a good source of energy and protein for a milking cow and can be used as a fibre source when feeding high sugar or starch feeds. However, a poor quality pasture silage (made from low quality pasture, or ensiled with low quality fermentation, or both) will not support high milk yield and will only be suitable for dry cows, or as a fibre source to reduce risk of acidosis.
Losses when making pasture silage
Losses occur as sugars and protein in the grass is broken down by enzymes, and bacteria. This process starts as soon as the grass is cut. Losses decrease quality as well as quantity, because it is the highly digestible components which are most rapidly broken down.
Losses during harvesting
Losses depend on the dry matter (DM) of the pasture. The optimum DM for silage is 25-30% because total DM loss is minimised.
• Cut in the morning of a sunny day, for rapid wilting. Cutting after 1-2 days’ sunny weather will result in good sugar levels in the pasture, even when cut in the morning.
• Avoid wilting for any more than 24 hours.
• Compact the silage well. In a stack or pit, use the heaviest wheeled vehicle available.
• Tractor wheels should not sink into the pile of pasture any further than the depth of rubber.
• For baled silage make sure that a high density baler is used.
• Seal the stack completely with a weighted, airtight cover. Wash old polythene before use to avoid contamination with the wrong bacteria.
• Don’t re-open a covered stack to add more pasture on another day
Losses while grass is in the stack, pit or bale
Once the silage is sealed, nothing can be done to change the fermentation process. Poor fermentation (e.g. air in the stack) leads to major losses of protein quality. In poorly preserved silage protein is broken down into ammonia, which decreases the feeding value of the silage. Getting things right while the grass is being harvested will maximise the chance of having a good fermentation:
• A fast wilt to 25-30% DM will leave good sugar concentrations in the pasture.
• Quick compaction and effective sealing will keep out oxygen, making conditions more suitable for bacteria to convert sugars into lactic acid.
• Fast production of lactic acid will quickly reduce the pH, to prevent protein losses.