This week sees the end of another round of meetings with the Irish Farmers Journal grassland management courses. Due to social distancing restrictions, our courses this month were held online.

The focus this month was how to use PastureBase and making decisions based on the grass wedge, which I previous went through here in The Grass Week.

In the meeting, we also discussed current issues on the ground in relation to grassland management. One of the main topics discussed this week was 36-hour grass allocations and why they are so important.

Once farmers start the second rotation, they should move to 24- or 36-hour grazings.

Graze hard

If you give the cows enough grass for 36 hours, you ensure they get all the grass they can eat for two grazings and only force them to graze hard on the third grazing when some animals may not get to eat their full intake.

However, the cows will be going into a fresh paddock with lots of grass in the next grazing and will quickly make up for the shortfall from the previous grazing.

If you graze a field for longer than 36 hours, the problem arises with regrowths

This means all animals are able to get enough grass intake each day to support their dietary needs for maintenance and production, which is essential coming into the breeding season.

If you graze a field for longer than 36 hours, the problem arises with regrowths.

After 36 hours, grazed grass will start to come back and as this will be the fresh leaf in the field, cows will eat the new fresh leaf appearing, significantly slowing down the growth of that paddock for the next rotation.

On the other side, when you only give the cows enough grass for one grazing, you start to restrict animals, although you might find it easier to get a good graze-out.

Performance

What happens is the weaker animals in the herd - for example, the first calvers or lame cows or thin cows - won’t get their full intake of grass between milkings, as stronger, more-dominant animals will ensure they get their fill first.

This will hit production and the performance of those weaker animals in the herd, which can lead to a bigger problem during the breeding season, as poor nutrition is one of the biggest causes of poor fertility in dairy herds.

So, from now on, farmers need to be implementing 36-hour allocations where possible and, if not, at least 24-hour allocations.

The key to maintaining good graze-outs is really keeping pre-grazing yields below 1,500kg/ha or even closer to 1,400kg/ha.

The best clean-out results from farmers on 36-hour grazings where a farmer would fence off 10% of the field to leave a strip of fresh grass for the last grazing to settle the cows in the paddock after milking on that third grazing.