Grass Watch 21


Grass Watch 2021

Grass Watch is designed to demonstrate the value of grass in milk production and the impact this variable food source can have on key components such as butterfat and Protein(%).
This key information on grass quality can help shape a feeding program to achieve the results of a modern day high yielding herd. Samples are taken Weekly every Monday from the Paddocks the cows are grazing and are sent off to be analysed. 15 monitor farms are used across Ireland and are combined to achieve average. One of the farms is a Corby Rock customer farm belonging to father and son Tom and Edward Treanor. Program runs until November.
 If you would like to receive weekly updates please submit your interest in the form on the right.

Overview of this week results by Trouw’s Dairy Technical Support Coordinator 

Grass Quality Summary:

  • Grass dry matters remained high at the start of last week averaging 18.6%. Grass dry matters of around 16% were recorded under continuous rain conditions whilst dry matters were around 20% under mainly dry conditions. With wide spread thundery showers at the end of last week and continuing into this week grass dry matters are expected to be more in the region of 13-16% for many, impeding dry matter intakes considerably (expected >2kgDMI/head/day less).
  • Grass quality and digestibility remains very good, ME averaging 12.5MJ/kgDM
  • NDF’s dropped again slightly from 36% week previous to 34% last week. This further drop in NDF was mainly due to premature entry at low pre-grazing covers of 1200-1300kgDM/ha in many cases compared to mainly 1400-1500kgDM/ha week previous. Low fibre in grass together with early entry at low covers will pose an extremely high risk of milk fat depression.  In practice, milk fats are falling considerably across many farms at the moment.
  • Based on current daylight hours, grass digestibility and dry matter, ‘maximum’ expected dry matter intake is 16kgDM/head/day – capable of supporting maintenance requirements plus 22.5 litres. Cold nights continue to depress potential dry matter intakes during the evening and early morning. On days of heavy showers expect ‘maximum’ potential dry matter intake of grass  to be no higher than 12-13kgDM at best – supporting maintenance plus 13.5-15.7 litres. On days of light rain expect ‘maximum’ potential dry matter intake of grass to be 13-14kgDM at best – supporting maintenance plus 15.7-18.0 litres.
Full-time Grazing – *Maximum* Housed by night Small quantity of buffer silage prior to evening milking
Grazed Grass (kgDM) 16.0 8 14
Grass Silage (kgDM)


5 0.5-1.0
Milk from forage (L/head) 22.5 15.5 19.0-20.0

Note: these are considered ‘best case scenarios’ (maximum to be expected)

  • Grass sugars continued to rise to 15.8%, much higher than we have recorded in previous years.
  • Crude proteins continued to fall to 18.2% last week- for many farms crude proteins were around 16% last week. Milk urea’s across monitor farms currently range from as low as 12mg/dl to as high 28mg/dl. Farms experiencing milk ureas repeatedly in the low teens should consider the need for additional protein supplementation.
  • Risk of milk fat depression from RFC, Acid Load (both a result of high sugars) and Fibre index remains ‘extremely high’ and indeed much higher than we have seen in recentyears. Risk from RUFAL (unsaturated oils) remains ‘low’. Butterfat levels have dropped significantly over the last couple of weeks – keep in mind the factors mentioned in the management notes to maintain butterfats as it is always hard to recover butterfat levels once they crash.
    Trouw Nutrition - Claire Beckett

    Trouw Nutrition – Claire Beckett

Management Notes:

A lot of issues occurring across farms at the moment, including many cases of PICA, butterfats falling, disappointing milk peak yields and persistency post peak and low milk ureas.

Be pro-active in adjusting supplementary feed on wet days (see table below)


  Reduction in grass dry matter intake Additional compound feed required
Showery Weather 1kgDM/head/day 1.25kg
Continuous Rain 2kgDM/head/day 2.25kg

 Persistency Of Milk Yield Post Peak:

  • Many herds reached peak yield a couple of weeks ago. For some herds peak yield achieved was lower than typically achieved in previous years due to curtailed intakes of grass all season. After peak, milk yield will naturally fall, however for some herds litres have fallen sharper over the last two weeks than should be expected.
  • It is vitally important to be regularly measuring grass intakes as accurately as possible and hence supplementing accordingly to maintain persistency in yield– aim to curtail milk yield drop to <2% per week

For herds with milk ureas repeatly below 20mg/dl, consider the need for additional protein supplementation

Managing Butterfat:

  • As has been evident over the years prevention is always much more successful than treatment when it comes to managing butterfat levels
  • Milk fat drop is usually multifactorial meaning a number of things are likely contributing to a drop, which include:
  1. High sugars in grass – acidosis
  2. Lack of fibre – acidosis and shortage of the building block of milk fat
  3. Moderate levels of oil in grass reducing fibre digestion in the rumen
  4. Herd coming towards the end of negative energy balance when contribution of body fat to milk fat is less
  5. Peak yield and hence dilution effect
  6. Abrupt dietary changes – grass quality changing quickly moving to 2nd rotation / pulling out buffer feeds abruptly
  7. Slug feeding of compound in parlour (max. 4kg/milking) or too high starch content of compound

To help maintain butterfats:

  1. Offering a small quantity of effective fibre source until end of 2nd rotation – Chopped straw, straw pellets, wholecrop, maize silage, soya hulls, sugar beet pulp etc.
  2. Avoid excessive levels of nitrogen fertilizer and sow directly after grazing to maximize days between sowing and grazing
  3. Graze at the 3 leaf stage
  4. Avoid slug feeding concentrate in parlour – max 4kg/milking. Ensure cows aren’t coming into the parlour hungry then getting a slug of concentrate – monitor rumen fill and adjust allocation of grass as necessary
  5. Ensure starch level of compound supplement is appropriate for feed rate
  6. Avoid periods of feed deprivation
  7. Avoid abrupt dietary changes
  8. Avoid selective grazing – maintain sward quality. Pre-mowing can help maintain sward uniformity
  9. Include rumen buffers/neutralisers and/or yeast
  10. C16 protected fat can be included to artificially increase milk fat – consider economics first

Risk of PICA remains

  • With very low NDF levels in grass and very high sugars, combined with cold temperatures restricting phosphorus uptake there will be a risk of PICA in herds moving closer to full-time grazing
  • Signs of PICA – cows eating stones, briars, soil etc
  • Causes:
    • Low phosphorus
    • Low sodium (salt)
    • Poor rumen health / acidosis – lack of fibre, high sugars
  • Prevention/treatment
    • Ensure good rumen health – keep a close eye on dung score and milk fat levels and increase fibre content of buffer feed if necessary. Rumen buffers will also be helpful. Avoid any abrupt dietary changes
    • Ensure sufficient salt in diet. Salt blocks can be offered. Cows self-regulate salt so they will only consume it if they need it
    • Ensure sufficient phosphorus in diet. If phosphorus deficiency is the cause of PICA cows will take around 2 weeks to respond to the additional phosphorus

The dry matter (DM) content of forage (measured as a percentage) is the proportion of total components (fibres, proteins, ash, water soluble carbohydrates, lipids, etc) remaining after water has been removed.
Knowing the dry matter percentage of forage is important. The lower the dry matter content, the higher the fresh weight of forage required to achieve a target nutrient intake, whether this is grazed grass or conserved forage.

In Ireland, due to the climate, we typically have very low grass growth rates in the spring and again in the autumn, with maximum growth rates being achieved during the month of May. Although there is little we can do about the weather in the spring and autumn periods, there are a number of measures we can take to improve grass production at the shoulders of the season.

If you would like to be updated with the latest results fill out the below contact form and we will keep you up to date.

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Weekly Dry Matter

  • Min Dry Matter (%)
  • Avg Dry Matter (%)
  • Max Dry Matter (%)
  • CRM Monitor Farm Dry Matter (%)

Predicted Milk Yield From Grass Only: Based on Average Grass Energy

  • MY @ 12kg DMI
  • MY @ 14kg DMI
  • MY @ 15kg DMI
  • MY @ 16kg DMI

Crude Protein %

  • Min Crude Protein (%)
  • Avg Crude Protein (%)
  • Max Crude Protein (%)
  • CRM Monitor Farm Crude Protein (%)

Oil Process A

  • Min Oil (A)
  • Avg Oil (A)
  • Max Oil (A)
  • CRM Monitor Farm Oil (A)

ME     (MJ/kg)

  • Min ME (MJ/kg DM)
  • Avg ME (MJ/kg DM)
  • Max ME (MJ/kg DM)
  • CRM Monitor Farm ME (MJ/kg DM)


  • Min NDF %
  • Avg NDF %
  • Max NDF %
  • CRM Monitor Farm NDF %

Weekly Grass Growths (PastureBase Ireland)

  • kg DM/ha/day

Weekly Grazing Information

  • Grass ME (MJ/kgDM)
  • Grass Crude Protein (%)

Butter Fat Alert (Average)

  • RFC Intake
  • Acid Load
  • Fibre Index
  • RUFAL Intake

Turnout – Getting More From Grass

Short informative video on key essentials to maximizing yield from grass systems.

Energy from Grass