Assessing Sward Quality

The quality of pastures is influenced by the species of grass, previous management and whether or not clover is present in the sward. The presence of a large number of weeds or inferior grass species will compromise nutritional quality, as will large amounts of dead or dying leaves.

The aim must be to achieve a leafy well-managed sward where ryegrass is the predominant grass species. Winter is a good time to assess ryegrass quantity in a sward, by doing a stem base check to identify the proportion of ryegrass in relation to other grasses. Most perennial ryegrass have a red stem base and when the leaf underside is shiny, it is almost certainly ryegrass. By walking fields and randomly checking 10 to 20 plants in several metre squares, and counting the proportion, you can get an idea of ryegrass percentage content.

Target Ryegrass Content: Minimum of 50% of the sward, preferably 70% or more

In these swards nutritional quality will generally not constrain cow performance. The energy content of good, well-grazed ryegrass swards is consistent at above 11.5 MJ/kg DM.

Factors known to reduce sward energy content include:

  • Previous grazing residues.
  • Prolonged grazing intervals.
  • Poor species mix.
  • Poor pasture topping practice.

With clover in the sward at the target level protein levels will be a percentage point or two higher than in grass-only swards - around 18-20%. This will allow useful economies to be made in the protein content of any supplementary concentrates. The quality of swards, as measured by their organic matter digestibility, increases with the proportion of live leaf.

Live Leaf and grass sward digestibility

Target Live Leaf Content: Minimum 65%.

The proportion of live leaf in a sward can be estimated as follows:

Step 1: Take a range of grass samples from the sward, cutting down to a height of 4 cm.

Step 2: Mix the samples and take a 50 g sub-sample.

Step 3: Divide the sub-sample into two piles, one containing live leaf and the other all remaining plant material.

Step 4: Dry both samples in a microwave oven for 5-6 minutes.

Step 5: Calculate the live leaf percentage of the combined weights, as follows:

Dried weight of live leaf                           6.5 g

Dried weight of plant material                  2.8 g

Total weight (6.5 + 2.8)                           9.3 g

Live leaf percentage (6.5 ÷ 9.3 x 100)       70%