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Too much grass can be a problem too!

As we are heading into a period where grass growth exceeds grass demand, dairy farmers will need to be extra vigilant that they don’t fall into the trap of grazing grass covers that are ‘gone too strong’. James Moyles, Teagasc Dairy Advisor, Co. Offaly has options for managing grass and quality here

Grazed grass provides most of the energy, protein, and the majority of minerals in the diet of Irish lactating cows at peak production.  However, the quality of grass one dairy farmer is offering his stock can vary significantly from that of his neighbour. This can have large effects on the milk cheque and the feed bill at the end of the month.

The objective of every dairy farmer at this time of year should be to have cows eating as much grazed grass as possible. That said, it is important to point out that the quality (OMD) of the grass, as well as the quantity offered, will dictate what the herd actually eats.

Feeding grass that is ‘too strong’ has the double negative of (i) reduced cow intakes because this grass is less digestible and (ii) less energy per kg of grass DM.  This is why milk yield and protein % tend to slip in early summer even though cows have lots of grass in front of them every day.

Measuring grass quality

Organic Matter Digestibility (OMD) is the common measure of grass quality.  Grass that has a high OMD value will have a high energy content (measured in UFLs’), plus will be low in fibre.  Less fibre means less filling and this in turn means more can be eaten.  Grass with a low OMD value on the other hand, will be low in energy, have higher fibre, so less can be eaten.

In practice, we rarely see the 5kg of milk yield differential between the two grass qualities above.  Farmers not managing grass to the optimum will usually prop up their milk yields over the main summer months of May - July by feeding extra concentrate, so instead of feeding 1.5 – 2kgs/cow/day for CalMag/minerals, these farmers are typically feeding 3.5 – 4kgs/cow/day.  This will close the milk yield gap somewhat, but at a financial cost.  These farmers will also need to resort to the topper on a more frequent basis to arrest the decline in grass quality.

How can we maximise the quality/energy value of our grass?

The simple answer is to try to ensure that the grass plant we are offering to our cows is at the optimum 3 leaf stage.  During the summer months, this typically occurs approximately 19-21 days post grazing.  For farmers familiar with putting figures on grass covers, this equates to 1,300 - 1,500 kg DM/Ha or approximately 10cms in grass height.  What we are trying to achieve is the maximum amount of leaf and the minimum amount of stem in the sward.  This will only be achieved by constantly grazing down to 4cm post grazing height.  All of this sounds relatively straightforward in theory, but it takes a very good grassland manager so consistently achieve top quality in every paddock the cows enter.

Options to maintain quality

The following are some of the options open to dairy farmers to avoid running into grass covers that are ‘too heavy’:

  • Increase milking platform stocking rate:
    • Reduce area by closing ground for long term silage or taking land out for reseeding,
    • Bring back young stock such as breeding heifers to milking platform,
  • Decrease level of concentrate supplementation;
  • Remove grass surpluses as bales;
  • Reduce rate of chemical N being applied. 

Making an informed decision

Maintaining high quality grass ‘in front of your cows’ does not happen by accident.  It takes hard work and effort.  This begins by walking your farm to establish the amount of grass on your farm.  Top grassland performers use all the available information at their disposal such as weather forecast, their own previous week’s grass growth figures plus forecasted growth rates for their own area (see map below from Pasturebase).  This information gives them the confidence to make the best informed decision for the week ahead for their farms.  It is important to make a grass management decision and go with it.  You won’t always get it 100% correct, but the alternative which is often to procrastinate and do nothing will invariably be the wrong decision.  The rewards for getting grass quality right as outlined earlier are too big to be ignored.  Make it one of your farming goals to feed your cows as much quality grass as possible as often as possible.

Figure 1. – Grass Growth Predictions showing increased grass growth for the week ahead beginning 31/05/2021.

Read more here on Grassland Management or about Grass10 or about Pasturebase Ireland

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