As we are now in early June grass growth rates have exceeded 100 kg per hectare per day. There is exceptional growth at this stage of the year, with elevated air temperatures, high rainfall and plenty of moisture in the soil. Conditions are ideal for optimum growth but worth noting that dry matter digestibility (DMD) of the sward can deteriorate significantly, particularly once the proportion of stem to leaf ratio changes and when the plant flowers heads out.
Impact on Milk Protein
In the last fortnight grass growth rates have increased significantly leading to greater pre-grazing yields but reduced milk solids produced per cow. Milk protein can be depressed significantly if the pre-grazing yield exceeds 1,800 kg per hectare and predominately if there is a high content of stem in the sward. Energy intake is a key driver for milk protein synthesis and poor digestible grass can lead to a reduction in milk solids produced per cow.
Benefit of Grass Budgeting
Good quality grass with a pre-grazing yield of between 1,300-1,600kg per hectare can be up to 80% DMD, have an energy content of 0.95 to 1.05 UFL/ kg DM and a crude protein of 20-25%. The aim should be to have at least 10-14 days grazing ahead of dairy cows of which can be achieved with grass budgeting and removing surplus grass via baled silage. The aim should be to graze grass down to 4cm to have pre grazing yields of between 1,300-1,600 kg hectare and rotation length of 18-21 days to ensure high quality grass for dairy cows. Grass farm cover per cow should be between 150-170 kg per cow dry matter in May and August.
How to manage reduced grass growth
In periods of reduced grass growth it will be crucial to ensure dry matter intake, and more importantly energy supplementation is matched for each cow to reach targets for the overall lactation cycle. Unfortunately in such incidences where energy supplementation is not at the optimum for milk production, reduced reproductive performance can be a huge issue, particularly over extended periods in the grazing period. (See table 1 to show the requirement of energy supplementation at grass when grass dry matter intake is reduced).
Good grass management practises
Aim to maximise grass dry matter intake to achieve greatest milk yield and solids produced per cow, but most importantly it is crucial to know what the current dry matter intake of the herd is, by allocating grass daily and calculating the residuals following grazing.
Table 1: Energy Supplementation is dependent on Milk Yield and Dry Matter Intake at grass
|GRASS DMI KG DM/DAY||28 kg day||30 kg day||32 kg day||34 kg day||36 kg day||38 kg day|
|10||8.8 kg||9.8 kg||10.7 kg||11.7 kg||12.6 kg||13.6 kg|
|11||7.7 kg||8.7 kg||9.6 kg||10.6 kg||11.5 kg||12.5 kg|
|12||6.6 kg||7.6 kg||8.5 kg||9.5 kg||10.4 kg||11.4 kg|
|13||5.5 kg||6.4 kg||7.4 kg||8.3 kg||9.3 kg||10.2 kg|
|14||4.4 kg||5.3 kg||6.3 kg||7.2 kg||8.2 kg||9.1 kg|
|15||3.3 kg||4.2 kg||5.2 kg||6.1 kg||7.1 kg||8.0 kg|
|16||2.2 kg||3.1 kg||4.1 kg||5.0 kg||6.0 kg||6.9 kg|
|17||1.1 kg||2.0 kg||3.0 kg||3.9 kg||4.8 kg||5.8 kg|
*Source: Assoc. Prof. Finbar Mulligan, School of Veterinary Medicine, University College Dublin