Reinstating the residuales

Published 6 June 14

Reinstating the residual

Piers Badnell, DairyCo technical extension officer, explains why reinstating residuals and getting on top of rejection sites is crucial to ensure grass quality for the rest of the season.

We have had a wet spring, and many farmers have found the first round of residuals challenging. In some pastures, the result of this has been an increased stem to leaf ratio, and lower quality, which we have seen in the results some of our Forage for Knowledge farmer contributors.

On different farms I have seen increasing numbers of rejection sites and higher residuals over the last few weeks. If you don’t do something about this now, you will see decreasing quality later in the season, and with that a reduction in potential, and ultimately a reduction in profit.

In May and June, milk from grass is fairly easy. However, from the end of June onwards this can become harder if you don’t manage your grazing well. You may need to do something now to maintain quality and production from grass all season long.

From the end of June grass growth rates decline and, if not managed well, rejection sites increase and utilisation plummets as cows graze between these rejection sites. The grazed area reduces, and with reduced growth rate, the problem of supply is compounded. The pressure on the grass plant increases, as the round is shortened due to supply issues, so it is unable to get to its third leaf stage (link to 3 leaf article), 45% of the plant yield, compounding the supply problems.

To avoid this nightmare scenario, assess pasture now and look for rejection sites. Can you reduce their incidence? link to rejection site article. Grade paddocks on residuals – good, medium and bad. Those graded bad do something about this round, those graded medium do something about next round.

Pastures may look a bit worked and a bit tired, with rejection sites around dung and seed heads, and higher proportion of stem to leaf than wanted, with consequent reduction in quality. But principally the seed heads are normal this time of year. The grass plant wants to put a seed head up and you can’t prevent that, but the perennial ryegrass plant, unlike Italian ryegrass, only puts one head up in the year. So if you can remove this you can get back to leafy growth and quality.

If grass is grazed at two leaves at seed heading time the seed head is still low within the plant, and is relatively digestible. In late May early June grazing at two leaves reduces the impact of heading.

 Residuals 1

Image 1 - Paddock ready to be pre-mown

Residuals 2

Image 2 Cover of about 3,100 Kg/DM/ha, ideal for pre mowing

Residuals 3

Image 3 - Seed heads

By this time of year the sward may have been grazed five to six times, and just may seem a little tired. As cows have been out this long there will be some rejection sites, see above.

The best ways to reinstate the residual, and get rid of the seedheads and rejection sites, are by pre mowing, wilting and grazing, cutting for silage or by using youngstock / dry stock to tidy up for you.

If you are taking a silage cut big bales are probably the best way to remove the material and start again with the aftermath. When cutting for silage try mowing tight to recreate 4-5cm residual.

If correctly allocated, and with a good amount of grazing pressure, youngstock and dry cows can be used to take a sward down to reinstate the residual. But this needs to be quick, and cattle should not be left roaming around for weeks. Allocate a small area and graze down hard in a few days, then move on.

 Residuals 4

Image 4, 5 and 6 - Pre-wilting and grazing in practice

Residuals 5

Residuals 6

One first class method is to pre-mow wilt and graze the cut material. To do this well mow an allocation equal to what the cows will realistically clear up in a feed (aiming to mow to a residual of 1500kg DM/ha, about 5cm). Most people mow eight to 12 hours ahead of feeding, to allow for wilting to increase palatability. Cows are then turned in to clear up everything, including rejection site and seed heads, as long as they are not given in excess of what they can eat. As a result you get no waste, all grass is cleared and a reinstated residual, like a silage aftermath, for good quality regrowth.

 Residuals 7

Image 7 - Cows just before coming in for afternoon milking on the cleared area

The key to successful pre-mowing is grazing pressure. Only allocate what the cows will eat. Because they clear everything, this will generally be a slightly smaller area than you would have allocated for conventional grazing. Revaluate after each feed as a guidance for future allocations.

The conventional way to “tidy” up would be topping, but this method of pre-mowing wilting has many advantages over topping. Toppers generally cut too high and shred the plant when cutting, as opposed to cutting cleanly like a mower. This reduces regrowth and leaves lumps of material around the field which cows will not eat. This then blocks out light beneath the plants, and impairs regrowth. Finally the animals do not fully utilise the grass, put simply it’s a waste.

If you are removing grass that the cows are not eating, in a period where growth rates are slowing anyway, you are actually putting extra pressure on yourself due to this wastage. If you are going to top you will be spending money on diesel and your time, so why not use that time and money to create an opportunity as opposed to a waste?

Key points for successful pre-mowing

  • When you first start pre-mowing, cows won’t have come across it before so may not take to it straight away
  • Persist, accept a bit of waste for a day or two, and allocate a new area per feed
  • Don’t return them to what is a few days old - don’t forget once grass is cut it is starting its journey to compost!
  • The photos in this piece were taken on a farm which has just begun to pre-mow, wilt and graze. The cows took to it straight away, even on covers that were a bit too high
  • One trick is to make sure cows have an edge to their appetite when they go in to the pre-mowed area
  • Start pre-mowing in dry weather; make it easier for the cows
  • Allocate the right area, maybe slightly less than you would normally, so that there is real grazing pressure. For example, if a paddock is normally four grazings, with pre-mowing it will be more like five or even six grazings, simply because you will be clearing everything, so there is more material available to cows
  • You may in fact get increased dry matter intake as the pre-mowing makes it is easier for cows to take bigger mouthfuls, so they may eat more than in a normal allocation
  • Top covers for this method are about 3,000 – 3,300kg DM/ha, much more and the grass is to stemy and there is too much for cows to clear.

Some producers will decide to pre-mow the whole round at this time of year, in order to get all residuals reinstated, and others will pick individual paddocks that need it. This is a farm specific choice, made by looking at paddocks and assessing them individually for residual, rejection sites and seedheads.