Grazing: ‘Attention to Detail’

18 April 2020

by Claire Beckett, Dairy Technical Support Coordinator 

To achieve maximum litres from grazed grass whilst, maintaining milk solids, body condition and sward quality requires an eye for detail and pro-active management. The four key areas to focus on include:

  1. Turning cows out gradually

Lush spring grass is highly digestible and high in rumen fermentable energy, which if introduced to the diet too quickly can result in a sudden major drop in rumen pH. Signs of this include:

  • A drop in milk yield
  • A drop in milk fat percentage
  • Loose feaces

A decline in rumen pH may be inevitable given the high digestibility of grass, but the aim is to minimize this drop as much as possible by:

  • Building cows up to full-time grazing gradually over 3 weeks
  • Reduce the buffer feed gradually over this 3 week period. It is also helpful to keep the buffer feed as consistent as possible
  • Keep the fibre (such as straw) constant throughout this 3 week period.


Figure 1 shows a marked drop in rumen pH of 0.3 in a cow during the first week of turnout on a trial farm in Co. Armagh, where cows had rumen pH boluses and were gradually turned out to pasture over 3 weeks. In cases where cows are turned out to grass much quicker than this, the drop in rumen pH would be much more lower.


  2. ‘Intake is key’

To maximize grass intakes:

  • Target pre-grazing cover at 3000-3400kgDM/ha
  • Don’t force high yielding cows to skim out a paddocks - leave 1700-1800kgDM/ha (5-6cm) as a residual. Use corrective measures such as topped, pre-mowing and baling to replenish the quality of residual grass
  • Allocate the correct area, e.g.:
    • 100 cows
    • Pre-grazing cover 3200kgDM/ha
    • Target post grazing cover 1700kgDM/ha
    • Target intake 15kgDM/head/day
    • 100cows * 15kgDM / (3200kgDM/ha – 1700kgDM/ha) = 1.0 ha/day = 10,000m²
  • Check cows an hour before you bring them in for milking to ensure they still have sufficient grass and there is good rumen fill
  • Offer the buffer feed before evening milking so as not to impact on grass intakes
  • Maximise time spent at pasture – by minimizing time spent standing in the collecting yard
  • Graze at the 3 leaf stage to maximize intake and regrowth potential
  • Don’t forget water intake – sufficient drinkers available, clean water, good flow rate and short distance to access. Drinking troughs in collecting yards at milking times are useful.


  3. Maintaining milk fat levels:

  • Turn cows out gradually
  • Include rumen buffers and/or yeast
  • Graze at the 3 leaf stage – grazing before this will result in grass with higher oil content which can suppress milk fat
  • Sow fertilizer directly after each grazing and avoid sowing fertilizer in excess – nitrogen application and fewer days between sowing and grazing is associated with higher oil content in grass
  • Avoid feeding more than 8kg/day (4kg/milking) through the parlour on full-time grazing. If more needs to be fed it should be fed as part of a buffer feed
  • Ensure cows come in for milking with a full rumen. Avoid feeding concentrate on a relatively empty rumen
  • For those with historical issues of significant milk fat drops at grass it may be worth keeping a small amount of a fibrous buffer feed in until end of 2nd rotation
  • Avoid feeding quickly fermentable energy sources e.g. fodder beet as part of a buffer feed, this can be too quickly fermentable to complement lush grass


  4. Parlour feed settings

  • Be realistic on how the milk yield you should expect off grass. Table 1 outlines the maximum yield that can be expected off grazed grass alone. This requires good weather, excellent grass quality and maximum grass intakes.
  • Be proactive in adjusting feed settings during wet weather when grass intakes are reduced – expect 1-2 litres less during showery weather and 4-5 litres less with over one week of continuous rain.



In summary, to optimize performance at grass transition cows onto grass gradually, focus on strategies to maximize intakes and be dynamic in adjusting feed settings.