Autumn grass - good bad or indifferent?

Published 29 August 14

Autumn grass; good, bad or indifferent?

Piers Badnell, DairyCo technical extension officer, discusses the opportunities that lie in autumn grazing.

Carefully managed autumn grass, though often undervalued, has the potential to provide high-quality forage, allowing savings on feed and housing costs. To get the most from it requires understanding of what it can and can’t do.

The picture below (Figure 1) was taken in late September 2012 and is an excellent example of how good grass management throughout the season can leave a high-quality sward with a high leaf-to-stalk ratio and minimal waste.

Figure 1 autumn grass

Figure 1 Autumn grass management

So, how do we take advantage of this high-quality sward, and avoid drops in production and body condition?

First, we need to know how much is eaten and what it is worth. The examples below show how this is worked out, and the opportunities it creates.

Example 1

  • A 600kg cow requires 70MJ ME for maintenance
  • She will need 5.3MJ ME per litre for a 4% fat and 3.3% protein litre of milk
  • If this cow consumes 10kg DM of 12 ME grass, this then gives her 120MJ ME
  • Take off 70MJ ME for maintenance, leaving 50MJ ME
  • Divide this by 5.3 and this equals 9.43 litres of milk.

Example 2

  • In contrast, if she consumes 14kg DM grazing at 12ME that is a total of 168MJ ME
  • Take her maintenance, 70MJ ME, from this and that leaves 98MJ ME
  • Divide this by 5.3 and this equals 18.5 litres of milk.

(Source for calculations DairyCo Feeding+ manual chapter 7 (link))

Daily cow intakes depend upon: grass supply and demand, stage of lactation, weather, and will vary from farm to farm.

Grazing still makes up the largest part of the diet for the cows of the Forage for Knowledge contributors. For example, Matt Senior’s (link), in Somerset, cows are grazing 15kg DM each day with 1kg of concentrate per day, and produce 14.5 litres. The Jersey herd is 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’ (link), cows are grazing 15kg DM per day, and receive 2kg concentrate. At the moment, Keith is trying to raise covers to extend the round, so the concentrate is in there to reduce demand on the grass. If he did not want to raise covers, grass intake would be 17kg.

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

What about Holsteins? At a recent discussion group, the members  predominantly had Holstein and were still grazing hard, with mid to late lactation cows (herd averages were in the 8,000 to 9,500 litre range). Daily grass dry matter intakes were between 11 and 15kg per cow. The group’s 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.

So, with good management there is still plenty of milk in autumn grass. The key is understanding and management.

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

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

The Table 1 below from Grass + Chapter 6 page 8 (link) complements this information from SRUC

Table 1 Supplementary concentrate levels for higher yielding cows

Table with source

 

 

So the potential is there, as shown by grass quality. Autumn usually provides good growth rates to provide the quantity, and the experimental work shows what is possible as seen above. The key is how much is to calculate what the cow is actually eating against her requirement, as there is plenty of evidence to suggest if you overestimate this, the potential for body condition loss is there, with the knock on effects of yield and fertility in the next lactation. This is especially the case for the more Holstein-type cow. Grass-based genetics will tend to look after themselves far better. So, to be sure measure how much your cows are eating, and balance where necessary.

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

Last year on 10 September I took three grass samples from the same spot in a grazing paddock, at different times of the day, in order to see how dry matter varies. 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 06:30, 11:30 and 17:30. The temperatures were 9° C, 16°C and 18°C. The dry matters were as follows:

  • 06:30 – 15.1%
  • 11:30 – 24.4%
  • 17:30 – 24.2%

What I think this shows is that if we time cows grazing we can maximise the dry matter intake. Some herds will be supplementing 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 12ME grass. So, does this mean supplementation around morning milking so that by the time the dew has gone, the cows have an edge of appetite to maximise grass intake? What do you think? This sampling is 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.

The new Recommended Grass and Clover List has information on growth performance for each variety in, for example, autumn or spring, so when selecting varieties for reseeds you can tailor what you want to suit your grass production requirements.

The key is that there is a grazing opportunity in the autumn, and if we know the true potentials from the science and trials that have taken place, and it’s backed up by what people are actually doing on farm, we can take advantage of autumn grass and profit from this opportunity.