Grass silage Part 2



In the second part of this series, Wim Hofman, cattle specialist for De Heus Animal Nutrition in the Netherlands, continues his discussion on managing pasture for production. Lloyd Phillips (Farmer's Weekly)reports.

Good pasture managers apply appropriate fertiliser treatment, based on regular soil and grass sampling, analyses and recommendations.

Inorganic fertiliser has the advantage of being able to be measured and applied in a controlled way to meet the specific requirements of the pasture. However, it represents a significant cost in pasture production. Applying too little will impact negatively on the pasture while too much will waste money and can damage the environment and affect the health of the dairy herd.

Organic slurry on SA dairy farms is full of nutrients and microbial life beneficial to soil and grass. It can be used to cut down on the dairy operation’s fertiliser cost. To benefit from dairy slurry, a farmer should have it analysed for nutrient content, as levels can vary due to changes in the feeding regime.

While South Africa lacks average figures for dairy slurry nutrient content, studies in the Netherlands have confirmed its value in pasture production. Total nitrogen (N) content averaged 4,4kg/ m3 of slurry, phosphorous (P) 1,6kg/ m3, potassium (K) 6,2 kg/ m3, magnesium (Mg) 1,3 kg/ m3, and sodium (Na) 0,7kg/m3.

“I recommend that SA pasture-based dairies use a combination of inorganic fertiliser and organic slurry to enhance the palatability and production of their pasture,” says Wim.

When it comes to the appropriate grazing or harvesting time for pasture grasses, European dairy farmers use the height of the grass as a measure (Table 1) while SA dairy farmers use the leaf stage in the grass’s growth cycle.

Wim explains that in Europe, dairy farmers graze their pastures at a height of 15cm to 20cm or cut them when they are 25cm to 30cm, while SA dairy farmers put cows in to graze at the three-leaf stage. During the SA summer season, pasture grasses are taller at the three-leaf stage than at the same stage during winter.

Whether the pasture is assessed on height or on leaf stage, the sward should be optimal for the milking herd.

The dairy cow is the most cost-effective and efficient harvester of pasture grass. However, if a dairy farmer cannot graze his pasture at three-leaf stage, he should cut and wrap, or ensile the grass in a pit. This will give him a bank of supplementary roughage.

“Pasture grass should not be cut to below 6cm above the surface as this removes nutritional reserves stored in the bottom third of the stem,” Wim warns. “These reserves allow grass regeneration after grazing or cutting. To maintain uniform and optimal regrowth, after every second grazing a pasture should get a cleaning cut.”

He adds that irrigation and oversowing pasture must be carried out properly when necessary for grass production. Drainage should be adequate enough to prevent waterlogging after heavy rain.

A European study shows that well-managed pasture has about a third more feed units of energy (VEM)/ha than pasture with undesirable grass species and weeds.

When comparing dairy nutrition quality and its effect on milk production, De Heus uses the world standard that to produce 1kg of milk a dairy cow requires 460 VEM. Using this standard to compare the two pasture qualities reveals a difference of 3 014 units VEM/ha and 6  552 ℓ/ ha of milk produced.

Wim stresses the importance of regular sampling and analysis of ensiled grass to show which nutrients are lacking and which are excessive in the grass and soil of the pasture.

Silage pits are layered with grass harvested from different pastures at different times, so sampling must be carried out at various depths in the pit to generate an average nutritional value from that particular pit. A grass silage pit should also be sampled at various times because the average nutritional value of the ensiled grass will vary as it ferments in the pit. A dairy farmer can then adjust concentrate amounts accordingly to maintain the desired milk production.

It is important to know that the results of soil, pasture grass and grass silage analyses do not always reflect the roughage quality that ends up in a dairy cow’s digestive system. These are tools that the farmer must use for efficient pasture management.

“Sample results and the actual quality of the feed fed to a cow should be as close as possible on a dairy farm. This is attainable with well-managed pasture and grass silage production,” says Wim.

“If your pasture is properly managed, roughage quality will be good, intakes will rise and there will be more milk in the tank.”

Tricky terms defined
Silage – A crop harvested, while green, for fodder and subjected to anaerobic fermentation.
Organic – Derived from living organisms.
Slurry – A suspension of solid particles in liquid, as in a mixture of dung and water.
Oversowing – Sowing seed into an existing pasture.
Dry Matter (DM) –
A measurement of the mass of something when completely dried. The DM of plant or animal material would be the solids, with the moisture content excluded. Feed DM includes carbohydrates, fats, proteins, vitamins and minerals.
VEM is a measure of energy in feed expressed as VEM/kg or VEM (x 1 000/ha).

Related articles

Grass silage Part 1
Grass silage Part 3
Grass silage Part 4