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 below seasonal norms at the start of last week averaging 16.6%, reflecting the rain from the previous week. Grass dry matters will have increased over the course of last week with dry matters up around 20% and above on farms where no rain had been received in over a week. Those suffering from extreme droughts, where grass is scorching, expect grass dry matter in the region of 22-30%, similar to what was experienced during the drought in 2018.


  • Crude proteins are rising on farms, averaging 23.5%CP, with all samples testing above 20%CP last week, due to sufficient rain received at the start of July followed by the high temperatures last week, greatly improving nitrogen uptake and utilisation. As a consequence of improving nitrogen utilization grass sugars have dropped back to 10% and oil levels have jumped to 4.5%. Grass oil levels will also be influenced by drought conditions as grass increases its waxy cuticle.


  • As a consequence of increasing protein and decline sugars, excess rumen degradable protein (RDP) levels in the diet are rising – this will be reflected in rising milk ureas levels which in practice have increased from 17-22mg/dl previously to 23-26mg/dl last week. Milk ureas are expected to rise closer to 30mg/dl . With this excess RDP comes an energy cost to expel the excess rumen ammonia – currently estimated to cost 0.77L/cow/day


  • Grass quality is good at an average ME of 11.4MJ/kgDM, consistent with seasonal norms.


  • Maximum expected grass dry matter intakes are currently 16kgDM/head/day estimated to support maintenance plus 18.7L. To achieve 16kgDM requires good grass quality, pre-grazing covers at 1400-1500kgDM/ha, swards cleaned out well on previous rotation, weather conditions good and correction allocation of grass offered to achieve target intakes. Last week with heat stressed conditions grass intakes of 14.5-15.5kgDM were more realistic, with cows in practice taking off 15.5-17.5 litres from grass.


  • Risk of milk fat depression from RFC and Acid Load (both a result of high sugars, and digestibility of the fibre) has dropped to ‘moderate’. Risk from Fibre Index is moving from ‘moderate’ to ‘low’. Risk from RUFAL (unsaturated oils) is moving from ‘low’ to ‘moderate’.
Trouw Nutrition - Claire Beckett
Trouw Nutrition – Claire Beckett

Management Notes:

Last  week was extremely challenging for cows with heat stress negatively impacting on grass intake, milk yield, milk fat and protein, somatic cell count (including incidence of mastitis) as well as fertility. Hopefully as herds recover this week, keep in mind the following points:

  1. Maintain regular farm walks (at least once weekly)
    Focus on recovering a ‘wedge’ of grass covers
  2. Ensure fertilizer is sown ahead of the forecasted rain, especially in parts of the country where grass growth is really struggling
  3. Be cautious of a luxury uptake of nitrogen once rain comes – keep an eye on milk ureas and carry out a pre-cut test before cutting silage or removing surplus bales
  • Be cautious of oil levels in diet, especially with drought stressed swards
  • Time to consider completing a forage budget for the winter
  • Ear mark the poorest performing paddocks for August reseeding

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

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

Crude Protein %

Oil Process A

ME     (MJ/kg)


Weekly Grass Growths (PastureBase Ireland)

Weekly Grazing Information

Butter Fat Alert (Average)

Turnout – Getting More From Grass

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

Energy from Grass