Senior scientist, farms systems, Kevin Macdonald and DairyNZ principal scientist, animal science, John Roche, set out fundementals to making great silage.
- Pasture cut for silage must be of high quality.
- Grazing residuals should be 1500-1600kg DM on paddocks to be closed for silage.
- Silage paddocks should be closed for no longer than six to seven weeks.
- Cutting, packing and covering the stack must be done quickly to reduce spoilage losses. Some inoculants can improve the fermentation process.
- Take care to minimise losses both at the stack and in the paddock/feed pad.
Pasture silage is a major source of supplementary feed on New Zealand dairy farms.
Making high quality pasture silage should not be difficult, but it must be viewed as an investment in supplementary feed, rather than just a necessity to manage pasture. New Zealand experimental results indicate that increasing silage quality by 2.3 MJ ME/kg DM increased MS production by 13, 17 and 41 percent in spring, summer and autumn, respectively1. Higher quality feed will also increase BCS gain/kg DM eaten.
Making of silage should only be done from a true surplus and the objective is to preserve as many of the original nutrients as possible. In practice, however, silage is often not made at the optimal time, and little attention paid to the silage-making process.
What is silage?
When grass is cut and left in a heap, it rots! Silage-making is the process of “pickling” pasture to reduce the pH (acidity) to a level that stops the feed “rotting” (i.e., stops microbial activity). This is achieved through “packing” the pasture and covering with plastic to exclude air, while microorganisms “burn” the sugars in the grass to produce lactic and acetic acid. If the silage is exposed to air (e.g. torn plastic), a chain reaction occurs that reduces silage quality.
Should I be making my silage in bales or in a stack/pit?
Pasture silage can be made either in a field stack, a pit/concrete bunker (on top of the ground) or as bales. Provided the quality of the material going into the silage is the same and proper attention is paid to compacting and covering the pasture, pasture silage quality should be the same from either stack/pit or baled silage. The decision to make bales or stack/pit silage is generally dependent on the farm system, the method of feeding silage and the infrastructure available for silage storage.
- Baled silage is more costly but enables flexibility for crop size and storage location on-farm and feeding out of small amounts on set occasions.
- Stack silage can also be stored in multiple locations and is cheaper than baled silage.
- Pit/bunker silage does not offer flexibility in storage, but, when properly used, will result in less wastage. Pit silage is easier to compact and, therefore, expel air.
Making high quality silage in practice
Rubbish in, rubbish out
The pasture you put into a stack cannot improve in quality. Therefore, it is important to ensure that the pasture to be ensiled is as high quality as possible and that the pasture has a high ryegrass/clover composition.
The drive for higher silage yields/ha to reduce the cost/t DM of making pit or stack silage has often been used as an excuse for ensiling “overgrown” pasture (i.e. pasture that has been growing for too long since its last grazing). New Zealand data indicates that pasture quality does not decline between 10 to 40 days after grazing in early spring2. Yet, on some farms, silage is often made more than 50 days after closure, with poor ensiling results (ME<10.5 MJ/kg DM and crude protein <15% DM2), plus there is an added disadvantage of a slower regrowth after harvesting.
Wrenn and Mudford3 reported that with later closure of the paddock, pasture quality declined earlier due to increased seed head emergence. Their data from both Waikato and Taranaki indicates that silage can be made six to seven weeks after closing without major loss in quality when the final grazing was in the two weeks before balance date. When the silage area was closed two to four weeks after balance date, there was a significant drop in pasture quality within three weeks of closing because of seed head emergence.
As well as the closing date effect on silage quality, Wrenn and Mudford3 also noted an effect of post-grazing residual before closing. Their data indicated that for every extra 100kg DM/ha increase in grazing residual above 1500kg DM/ha in the grazing before closing for silage, pasture should be closed for 1.4 days less. Nitrogen fertiliser can be applied at 30-50kg N/ha to increase pasture growth and subsequent silage yield.
To inoculate or not
When a crop is ensiled, the bacteria naturally present turn sugars into acids. To aid this process, inoculants are often applied to increase the population of “desirable” bacteria, thereby ensuring a more rapid reduction in pH and speeding up the ‘pickling’ process.
There are many different types of inoculants on the market. The most effective inoculants will be those that reduce pH quickly, produce the most lactic acid relative to acetic acid, and increase the time taken for the silage temperature to rise when the stack is opened. Choose carefully to ensure you get an inoculant that will improve your silage quality.
Field losses can be minimised by ensuring the paddocks chosen for silage are the largest paddocks, to minimise machinery turning, rectangular shaped, to avoid more corner losses than necessary, and that water troughs and other obstacles (e.g. electricity pylons) can be easily avoided. Even in the best conditions these losses will be 5-10 percent of the pasture available4. If not careful, losses can be greater than 25 percent.
Losses in the stack can be minimised by:
- reducing the length of time that the cut material is exposed to air
- ensuring the stack is well packed and promptly covered with plastic
- ensuring that the entire stack is covered in tyres (tyre to tyre touching) to hold the cover in place.
Feeding out losses can be controlled by allowing the silage sufficient time to ferment and by ensuring the correct shape of stack/pit for herd size. Depending on the inoculants used, the stack should not be opened for three to four weeks after closing. The face should be cleaned daily to ensure the material at the front is not exposed to air for longer than 24 hours and movement of the silage within the stack should be minimised (preferably through use of a block cutter/shear grab). Wastage at feeding out is best reduced by using a trough or a feed pad so cows cannot trample it into the ground.
Deferred grazing is the practice of holding over pasture that is considered to be surplus to requirements and grazing it at a later date. For example, if a surplus is identified in late October/November, the surplus area will be skipped and not grazed until at least February. Advantages in doing this can be:
- reduction in farm costs, through avoiding the expense associated with making silage
- use of pasture to better fit feed supply/demand.
When used as part of a low cost farm system by McCallum et al.5, they reported that it was more profitable than a traditional hay-silage system. The profitability was from an increase in MS production and no conservation costs. Further, the natural reseeding that occurred as a result of the deferral doubled the tiller density of the perennial ryegrass and increased pasture growth by 15-19 percent in the following season.
To get the advantages of the natural reseeding through deferred grazing, it is important to not graze until the pasture has gone to seed. In the New Zealand research, the pasture was strip grazed as a ‘supplement’ to the grazing rotation and offered to the cows between morning and evening milking. They reported that mowing before grazing increased pasture utilisation but there was no increase in MS production5.
In times of fluctuating pasture growth, deferral of areas for short periods can be an effective method of pasture control, and is often referred to as “rolling deferred pasture”. In these cases the pasture may not be grazed for periods of 30-40 days. If doing this it is important to ensure that pasture utilisation is high as the grass is still growing and, because there is no seed drop, there is a reliance on good pasture growth immediately after grazing.
- Macdonald, K., Nicholas, P., Kidd, J.M., Penno. J.W., and Napper, A.R. 2000. The effect of pasture silage quality on milk production and liveweight gain of dairy cows. Proceedings of the New Zealand Society of Animal Production 60: 253-255.
- McGrath, J.M., Penno, J.W., Davis, K.L., and Wrenn, R. 1998. Effect of date and length of closure and post grazing residual on pasture quality for silage. Proceedings of the New Zealand Grassland Association. 60: 259-264.
- Wrenn, N.R.; Mudford C.R. 1996. Making quality silage. Proceedings of the Ruakura Dairy Farmers’ Conference. 48: 50 57.
- Davies, D. 2011. Silage insights – Bale silage production, improving silage quality and reducing CO2 emissions. http://www.dow.com/silage/tools/experts/improving.htm
- McCallum, D.A., Thomson, N.A., and Judd, T.G. 1991. Experiences with deferred grazing at the Taranaki Agricultural Research Station. . Proceedings of the New Zealand Grassland Association. 53: 79-83.
This article was originally published in Technical Series September 2016