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Dairy Notes May 2010

Grazing management

With the cold weather restricting grass growth in late March/April and delaying turn-out, a rapid improvement in growth conditions now could lead to problems maintaining grazing quality.  With no grazing wedge set up, a large part of the grazing area will become ready for grazing over a short period.  Action needs to be taken now to prevent grazing ‘getting ahead’ of the herd.
When your cows have been at grass for 10 days and grazing conditions are good, start grazing full time and stop buffer feeding.  The cows will have had time to adapt to a grass diet.  While autumn calvers may show an increase in yield the high yielding (>30 litres) cows may drop in yield 1.5-2 litres per head per day.  The loss in milk income will be more than covered by the 5-8 kg reduction in concentrate feed levels to these cows as you move from feeding medium/poor quality silage to high quality grass.
If there is a high number (30 +)  of fresh calvers yielding over 35 litres, and handling facilities allow, there could be a case for grazing them by day and housing at night if high quality silage is available.  In variable grazing conditions this gives more control over intakes, benefitting herd fertility and cow performance.  The problem with housing the whole herd at night is the extra expense of feeding silage and meal to stale cows which are already safely back in calf and capable of obtaining sufficient feed from full time grazing.  
Walk grazing areas twice per week to allow early identification of a grass surplus.  Ideally cows should be turned on to swards with a cover of 3300-3500 kg DM per hectare (15cm tall) and graze them down to 1600-1800 kg DM per hectare (6-7cm tall).  Check the weekly GrassCheck grass growth figures in the agricultural press or on the internet.  If your cows are grazing swards with covers over 4000 kg DM per hectare, the sward to graze in 10 days time has already a cover of 3000 kg DM per hectare

In good grazing conditions cows can produce at least 23 litres from May grass
and GrassCheck is predicting growth rates of 80-90 kg DM per day the grazing is going to get further ahead of the herd.  Cut surplus grass immediately for silage so that the sward will be ready for grazing again in early June.  Delaying cutting until the main silage block is ready for cutting will leave you short of grazing in early/mid June.

Silage – weather affecting crop maturity

Grass maturity at cutting has the greatest influence on silage quality.  For a target ‘D’ value of 70, you should cut at the first sign of ear emergence.  For each week’s delay in cutting an extra 2.2 kg of concentrates per cow per day would be required to maintain the same milk yield.
The cold weather this April/May has delayed the maturity of grass plants as well as growth rates.  Early grass varieties such as Donard and Moy will be heading several days later than normal -  as silage quality won’t suffer be prepared to put back harvest date to allow swards to bulk up.  In swards based on intermediate or late heading varieties heading is also likely to be later than usual but an increase in temperatures over the next two to three weeks could reduce the delay.

Wilting

The positive impact of feeding high dry matter silage on cow intake and performance is well appreciated - hopefully the weather this May will again favour wilting.  To achieve a target dry matter of 25 percent:
  • Assess dry matter (DM) before mowing.  If grass is wet when walked, the DM is about 15 percent.  If your boots are dry the DM is about 20 percent.
  • In ideal wilting weather a crop cut at 20 percent DM will reach target within eight hours if spread out but if left in a single swathe it will take 24 hours.
  • Even in good wilting conditions, crops cut damp will need to be spread if the target DM is to be achieved within 24 hours.
  • Avoid over-wilting which can produce unstable silage. If machinery breakdowns are going to delay lifting, row up swards to reduce the drying rate.