Teagasc advice for dairy farmers: Ideal pre-grazing swards and the level of fibre required

Grazing paddocks at the correct grass growth stage over the next two months is very important to meet the dual aims of:

* feeding your cows well;

* and hitting the correct post-grazing residual.

If covers are too low (less than 1,200kg of dry matter per hectare), daily intakes will suffer, and the grass growth rate may drop too.

If grazing covers are consistently too high (more than 1,700kg DM/ha), paddocks will not be cleaned out, and quality will suffer next time round.

Ideal yield

Research has shown that 1,400kg DM/ha is the ideal pre-grazing yield for mid-season grazing.

This corresponds to the three-leaf grass growth stage, and it applies across a range of stocking rates.

The following equation can be used for grazing management decisions.

Multiply stocking rate by rotation length by grass allowance, and add 100 to calculate the pre-grazing yield (1,400kg DM/ha).

These elements can be adjusted together to keep pre-grazing yield on track, where grass growth is variable.

If grass growth is very strong, and exceeding demand, rotation length can be reduced in the short term, by taking out bales, for example.

On the other hand, if growth is slow, then grass allowance should be reduced, and the rotation length increased, by adding in supplementary feed.

Grass fibre

Does ‘1,400 grass’ have enough fibre?

This is a question often asked in the early summer.

Plenty of articles are written claiming this ‘problem’, and advocating use of straw and/or feed supplements to ‘fix’ it. But what exactly is the level of fibre required, and how does high-quality grass compare?

Teagasc guidelines on fibre are based on neutral detergent fibre (NDF, an important fibre fraction in feed) and are based on a combination of international and Teagasc research work. The minimum NDF content for high-producing dairy cows is 32-34%.

High-quality ryegrass swards at 1,400kg/ha pre- grazing covers will, on average, have an NDF content of 36-42%.

This NDF is highly digestible and promotes high dry matter intakes. Therefore, there is adequate NDF for good rumen function.

Adding lower quality fibre (straw/silage) will not be of benefit. Where concentrate is fed, a fibre/pulp-based concentrate, with slowly-degradable starch will best complement high-quality grass.

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