Farm Ireland
Independent.ie

Monday 24 July 2017

Extend autumn grass rotations

It has been an excellent back-end to the year in terms of the acreage of silage harvested. Farmers above get in a late cut of silage outside Killygordon, Co Donegal
It has been an excellent back-end to the year in terms of the acreage of silage harvested. Farmers above get in a late cut of silage outside Killygordon, Co Donegal

Mary Kinston

August saw both extremes in terms of grass growth. Some of it was excellent while more of it was very dry, resulting in poor grass growth rates.

Each individual farm has its own set of circumstances, but many dairy farms came into this month with one of two extremely different scenarios:

1. Average pasture cover had decreased and was substantially behind target.

2. Average pasture cover was on target but some paddocks had heavy covers of poor quality.

Recently, I took a group to visit two farms, which highlighted these two extremes in pasture cover. Farm A had a stocking rate of 3.5 cows/ha and an average cover of 570kg DM/ha. It was in a clear deficit, though pasture quality was excellent. Farm B had a stocking rate of 3.2 cows/ha and an average cover of 870kg DM/ha, though at least four paddocks were heavy with covers in excess of 2,000kg DM/ha prior to a big dip in the feed wedge to lower covers.

I imagine most farmers would rather be in the comfort of the situation of farm B. This obviously requires less immediate action and less supplementary feed. However, for farm B, there was still some debate to what needed to be done with regards to when and how much feed should be introduced, and how to achieve good post-grazing residual covers on the paddocks without sacrificing both cow condition score and milk yield.

One of the visiting farmers highlighted the extremes of the two situations and asked me which one would I prefer to manage. The answer was simple -- farm A. Why? Because the set of decisions that need to be taken in a feed deficit are clear and simple. For those of you that have a lower-than-desired pasture cover this autumn, there are three actions to take:

  • Immediate action -- don't chance the recovery of a low pasture cover in the autumn.
  • Extend rotation length. In early September move to 1/35 (35 days) or 1/40 (40 days) if in a large feed deficit.
  • Reduce the demand for pasture (increase supplementary feeding or reduce numbers).

Autumn is a period characterised by the fall in pasture growth below pasture demand. Therefore when presented with a feed deficit, immediate and adequate action is required to limit the deficit becoming even larger.


If pasture covers fall to less than 300kg DM/ha, grass growth will also decline. During the autumn, it's an essential part of grass management to keep extending the rotation. This is important because falls in temperature and daylight result in slower leaf appearance rates.

Balancing

So, in essence, grass now needs more and more time to grow as we head further into the autumn. An extension in rotation length should initially provide an increase in pasture cover, which can then be pushed forward and grazed by cows later on in the autumn -- when grass growth is substantially lower than grass demand. However, this is a balancing act as building up too much will reduce tillering, resulting in tiller death and reduced feed quality.

Rotation length targets are shown in the table (below) in relation to the total area to be grazed per day by all stock classes. It is calculated from the total area available divided by the rotation target (eg, 30ha/35days = 0.86ha/day). These should be considered against your feed budget targets and the actual pasture cover presently on the farm.

Once 1/35 is achieved by September 15, at this stage you should look to the action required to achieve your next target of 1/40 by October 1. The final step is to feed your cows an adequate amount of supplementary feed in line with this extension in rotation length, or to consider other options to lower the demand for pasture.

These options can include getting youngstock or cull cows off the milking platform, drying off or milking once a day animals with a poor condition score which will calve early next spring (February calvers).

Scanning your cows now and using your latest milk recording results can be excellent tools to provide information that will help you make the right culling and drying-off decisions. For example, any cows producing less than 0.5kg MS/day could be considered for drying off -- or cows with a repeatedly high somatic cell count.

Thankfully most farmers have received rain and the last of the fertiliser has been or is being applied. However, if your grass is in short supply, react now to have a fruitful autumn.

  • Dr Mary Kinston is a farm consultant who works in Co Kerry and Co Clare. Email: maryk@primefields.co.uk

Irish Independent