Is there an opportunity for autumn grass

Published 13 September 13

Exploiting autumn grass

Autumn grass is often undervalued, but carefully managed, has the potential to save on feed and housing costs. Piers Badnell, DairyCo extension officer, discusses the opportunities presented by autumn grazing.

But the key is being able to take advantage of this opportunity while avoiding a drop in production and body condition.

First we need to know how much is eaten and what is it worth.  See the example below of how this is worked out, and the opportunities it creates.

  • A 600 kg cow requires 70 MJ ME per day for maintenance.
  • She will require 5.3MJ ME per litre for a 4% fat and 3.3% protein litre of milk.
  • If this cow consumes 10 kg DM of 12 ME grass this will give her 120 MJ ME.
  • Take off 70 for maintenance, leaving 50 MJ ME
  • Divide this by 5.3 and this equals 9.43 litres of milk.
  • In contrast if she consumes 14kg DM grazing at 12 ME that is 168 MJ ME.
  • Take her maintenance of 70 MJ ME from this and that leaves 98 MJ ME.
  • Divide this by 5.3 and this equals 18.5 litres of milk.

(Source for calculations DairyCo Feeding+ manual chapter 7)

Daily cow intakes will depend upon grass supply and demand, stage of lactation and weather, and will vary from farm to farm. For example at Matt Senior’s, in Somerset, cows are currently grazing 15kg DM each day with 1kg of concentrate, and producing 14.5 litres. The herd is Jersey, producing 5.6% fat and 3.8% protein, which on a standard litre converts to an equivalent of 18.5 litres.

At Lydney Park in Gloucestershire Keith Davies, cows are also grazing 15kg DM per day, and receiving 2kg concentrate. Keith is trying to raise covers at the moment to extend the round so the extra concentrate is aimed at reducing demand on the grass. If he did not want to raise covers, grass intake would be 17Kg and concentrate feeding lower.

Both these herds are spring calvers, with grazing genetics, and will currently be well into lactation, in the region of 200 days average in milk.

What about Holsteins? At a recent meeting of a discussion group with predominantly Holstein-based herds, mid to late lactation cows (herd averages in the 8,000 to 9,500 litre range) were still grazing hard and daily grass dry matter intakes were between 11 and 15kg per cow. Their calculations put milk from grazing between 10 and 17 litres. With these grass dry matter intakes the cow still has capacity to be supplemented and to achieve yields into the mid twenties, if that pays.

Data collected over the last five years in Forage for Knowledge shows that, if well managed, grass quality can be maintained at 12 ME all year. But as we move further into the autumn, grass growth will reduce and, unless covers have been built, availability will also reduce and intake potential will decline.

So what can we expect to achieve? A study from SRUC a number of years ago looked at the DM intakes of late lactation cows, yielding 20 litres per day. On a dry day, grass intakes were 15kg DM/day and in wet weather, 8-10kg DM/day. This gives a good guide of where you should be aiming.

As the days get shorter we are getting heavier dews, so what effect does this have on grass dry matter?

On Tuesday the 10th September I took three grass samples from the same spot in a grazing paddock at different times to see how dry matter varies through the day. This sampling was not high science – it was one day and in one place, and not replicated and should just be used as a guide or a point to consider.  But it does throw up some interesting points.

The day was dry, mostly cloudy with sunny spells and a gentle breeze. There was a heavy dew, as you would expect at this time of year. I sampled at 6.30am, 11.30am and 5.30pm. The temperatures were 9° C, 16°C and 18°C respectively, and the dry matters as follow:

  • 6.30 am – 15.1%
  • 11.30 am – 24.4%
  • 5.30pm – 24.2%

This shows that if we time grazing, we can maximise the dry matter intake. Some herds will be being supplemented to a degree, so if you want to maximise grass intake you need to make sure you are using the right supplementation to avoid substitution, and at the right time.

You want to encourage grazing peak once the dew has evaporated, so that every bite maximises dry matter intake of the 12 ME grass. So this suggests supplementation around morning milking so that by the time the dew has gone, the cows have an edge of appetite to maximise grass intake.

The key is that with good management, there is still plenty of milk in autumn grass.  If we know the true potential from the science and trials that have taken place, and it’s backed up by what people are actually doing on farm, then we can take advantage of autumn grass and profit from this opportunity.  The key is understanding and management.