Two or three leaves?

Published 23 May 14

Piers Badnell, DairyCo technical extension officer, explains why the three leaf grazing rule does not always apply at this time of year.

The grass plant has three live leaves; beyond this, the first grown leaf dies as a new leaf appears. When this happens stalk length increases and overall quality starts to decline. The first leaf is the smallest, with about 15% of yield of the plant, the second provides 40% of the yield, and the third is the largest with 45% of yield (Lee et al, 2010 Grasslands Conference). 

Grazing at three leaves ensures quantity at the time and quality in the future, as the plant has recovered from previous grazings by the second leaf stage and has the resources for its next round of growth.

But, at this time of year, with fantastic growing conditions, the leaves are very big (insert pictures) It probably measures well over 3,000kg DM/ha on the plate meter. This makes it very difficult for a cow to graze to a good residual, which we know is imperative to grow quality in the next round.

So you should stick at the 2,800kg DM/ha cover. Two leaves as an entry and accept the potential loss of the third leaf and 45% of the yield. In reality, if cows are unable to utilise the grass, we are not really loosing anything.

Therefore, when leaves are big and growth is good, grazing at two leaves is fine. An exception to this may be if you are pre-mowing and wilting, as the mower cuts the residual needed, rather than having to rely on the cows to graze down so hard.

As we head towards July, reducing growth rates and a dry summer will also slow down growth and reduce leaf size. At this point, you need to extend the rotation to take account of this drop. It is very easy at this time of year not to react quickly enough and to bite too hard into the wedge. When this happens, it is very difficult to get back into balance.

You need to slow the rotation quickly, so that at this point the plant definitely has three leaves and you can utilise that 45% of yield in the third leaf. Go too early or quickly and you could be grazing at two leaves and, by default, accelerating and exaggerating the slow up in growth, baring out the farm. Extend the round early and get the full potential to take you through the dry period.

During dry times, still aim to hit 1,500kg DM/ha residual as leaving too much means excess grass can act as a straw to dry out ground even quicker.

The key is knowing how the plant grows, measure monitor and plan. Ryegrass performs when worked hard, but hard in the right way.