Grass silage Part 3


Making grass silage while the sun shines

Although not commonly practised in South African dairy farming, grass silage production is likely to take off as dairy enterprises expand. Wim Hofman, cattle specialist at De Heus Animal Nutrition of the Netherlands, explains how to make quality grass silage. Lloyd Phillips (Farmer's Weekly) reports.

While the principles of grass silage production and maize silage production are the same, this important task is arguably one of the most challenging to master. Mistakes made in the ensiling process can prove expensive, leading to unusable or low quality silage, according to Wim Hofman, cattle specialist at Dutch animal nutrition company De Heus.

Poor quality silage is of sub-optimal nutritional value, reduces the intake of dairy cows and lowers milk production. It can also cause sub-acute ruminal acidosis.

Common sense tells the farmer that the better the quality of the grass, the better the quality of the silage. Table 1 shows significant differences between the nutritional value of fresh ryegrass and its grass silage when the ryegrass is cut late in the growth cycle, with too much stem and too little leaf. Digestible organic matter dropped by a significant 20% and energy values also differed.

In comparing dairy nutrition quality and its effect on milk production, De Heus uses the standard, where 460 VEM (feed units milk) is needed to produce 1ℓ milk.

Low sugar content in ryegrass has a negative effect on silage quality. In this case, lower quality fresh ryegrass led to lower quality silage.

“Energy is lost if silage is allowed to heat up excessively in the pit, and protein is lost if silage rots and releases ammonia. Poor quality grass silage can lead to high levels of butyric acid in the milk, making it difficult for the processor to produce quality products,” says Wim.

Grass silage provides better quality silage than hay and is less weather-dependent, as rain can set the hay- making process back.

Grass mown for hay must dry to a DM level of 80% before baling, while grass cut for silage can have a high moisture content.

In the southern hemisphere, grass cut for silage can be picked up within 24 hours, which means low nutrient loss between mowing and ensiling. Grass silage-making is also less labour-intensive than hay-making.


Timing is critical in silage making. Cut grass at the three-leaf stage of its growth, or at 30cm. Getting the balance right means taking advantage of leafier, young, more digestible material but striking the balance and getting bulk into the pit. In this way, the farmer can manipulate the feeding value of the silage.

“Tedding is easier if no more than 3,5tDM/ ha is harvested from the pasture at a time,” says Wim. “Mow on a sunny day to benefit from the higher sugars.”

Sugars of 2% to 3% in fresh grass mean sugars of 10% to 15% in the DM. Fermentation losses are low in pasture, which is above 25% DM, and grass should not be drier than 45% DM. The optimum DM content for cut grass going into the pit is between 35% and 45%.

“The grass must have the highest possible energy and protein content,” explains Wim. “Don’t cut it shorter than 6cm as this will reduce the regrowth. Ideally, grass should be cut into short lengths by a chopper harvester.”


The dairy farmer should aim to minimise the inevitable losses, including DM and nutrient wastage in-field. Pasture loses sugars to respiration while it waits to be picked up.  If the silage is not properly compacted, protein and organic matter can be lost with too much oxygen in the stack. This can also occur if the pH is too high.When air is present due to poor compaction, heat can be generated by the action of yeasts on nutrients, causing losses.Nutrient loss through silage effluent should be minimal, with a DM of above 30%.

Various techniques can improve silage-making. The crop should have a high sugar content for the best fermentation to occur.

Strategic tedding helps to dry the grass after mowing to get the DM right as quickly as possible. A DM level of above 45% will negatively affect the efficiency of the fermentation process in the pit.

If the DM level is below 25%, put in an additive to keep the pH low and stimulate lactic acid production.

“It is important to fill the pit layer by layer,” Wim stresses. “Don’t allow the silage contractor to rush this, as proper compaction forces out the air to create the anaerobic environment as quickly as possible.”De Heus recommends raking and ensiling no more than 4ha of grass an hour to ensure proper layering in the silage pit.

“Heavy machinery achieves good compaction. When the pit is full, quickly seal it with plastic silage sheeting and weigh it down to keep the ensiled grass compressed,” says Wim.

The seal should be inspected once a week so that any damage can be repaired quickly.At feed-out, move across the face cleanly and evenly to minimise unnecessary oxygen penetration. Properly ensiled grass can maintain quality for as long as anaerobic conditions are maintained.

Fats facts

 Silage value is dependent on timing, yield and quality.
Losses can be minimised with good management.
Filling, compacting and sealing the pit properly will ensure quality silage.

Related articles

Grass silage Part 1
Grass silage Part 2
Grass silage Part 4