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Wednesday 17 January 2018

We're off to a fine start, so don't spoil it with bad quality pasture

Mary Kinston

Cows are producing very well at the moment, with some herds now hitting over 2kg milk solids per cow per day. Paddock activity is also been notably high, with a large percentage of the herd exhibiting signs of oestrus.

These two factors, combined with good grass growth over the past few weeks, mean things are generally humming along very sweetly.

However, it is still very important that we remain diligent about our immediate situation. Breeding will have either commenced or will be about to in the next week or so, so it's imperative to maximise a cow's intake on pasture, which is reliant on maintaining grass quality. High quality pasture contains a high proportion of green leaf and a small proportion of stem and dead matter and this principle should be a key focus as we head from the second rotation into the third.

Pre-grazing yields have been rising over recent weeks and a few second rotation paddocks have presented with heavy covers of >1500kgDM/ha available. Where these have been grazed down by cows, achieving a good grazing residual of 3.5-4cm has become more challenging. Now the quality challenge is well and truly on. The highly digestible short vegetative pseudo stems have now become reproductive on many grass tillers, with a longer and less digestible true stem which is elongating, with nodes which are visible to the naked eye and easily felt when running the tiller stem through your finger and thumb.

Impact

To minimise the impact of the grass plant's desperate urge to reproduce and develop this stem, which will reduce the cow's ability to perform in terms of both milk production and breeding, it is important that we aim to constantly balance the herd's feed demand (kgDM/ha/ day) with the pasture growth rate. Essentially, the aim is to graze cows as generously as possible whilst preventing excessive pasture waste and losses in future pasture quality. So the aim is to offer just enough pasture to stop these stems developing by grazing them off.

Surplus grass management is what sorts the men from the boys as it can be fairly tricky. There are tools to help your management decisions and maintain this balance, but all of them are reliant on weekly monitoring of grass cover and knowing the desired pre-grazing yield that is required by the cows for each week.

The pre-grazing cover can be calculated as shown below and is often referred to as the "trigger level" as any pasture with a cover greater than this amount is presenting a surplus above the herds feed demand.

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Target pre-grazing cover = (stocking rate x intake of pasture x rotation length) + residual cover

For example, four cows/ha x 17kg DM grass/cow (-1kg ration/cow) x 20days + 50kgDM/ha = 1,410kg DM/ha

This target, alongside the residual cover target, should be used with the feed wedge to help you identify both immediate and upcoming surpluses and deficits throughout the main grazing season (April-- August).The graph (left) identifies the surpluses and deficits for the pre-grazing target calculated above.

In this example, there is an immediate surplus with the paddock covers in excess of the pre-grazing target and also a potential surplus in about two weeks' time. To manage such a surplus there are three management options to consider;

  • Accumulate a surplus on a small area to be conserved as pit silage/bales (long-term silage)
  • Surplus on a small area to be conserved immediately, often as bales (short-term silage)
  • Remove a small area of pasture and reseed or sow a crop that can be eaten after the period of surplus

All three options aim to prevent the immediate surplus manifesting into a surplus all over the farm and an overall loss of quality. After such a good start to the year, it would be a shame to compromise the cow at such a critical stage of her lactation. So walk the farm, create your feed wedge and act on the information accordingly.

Mary Kinston is a farm consultant based in Kerry. Email: mary.kinston@gmail.com

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