A Challenging Spring for Grazing

19 April 2021

Every grazing season comes with its own challenges, particularly this year with cold and wet conditions.

Turnout has been a slow and challenging process for many herds and a virtual impossibility for others.

As conditions slowly improve, regular reassessment of ground conditions and grass availability will allow calculated decisions to be made on the best timing for gradually increasing the proportion of grazed grass in the diet. Key things to bear in mind for turn-out:

Defining Turn-Out Criteria

For herds running a fully-housed group alongside a full-time grazing group, define criteria for selecting cows suitable for grazing. A realistic turnout criteria might be:

  • 33 litres or less
  • Settled back in-calf greater than 40 days
  • Body condition score 3.0

 

Potential Milk from Grass

Table 1 outlines target dry matter intakes (DMI) and potential milk yield from grazed grass for April and May. ‘Excellent’ reflects excellent grass quality, entry at correct pre-grazing covers (2900-3200 kgDM/ha), correct allocation of grass to achieve required intakes, as well as good weather.

Table 1: Target DMI at grass and potential milk from grass

 

April

May

 

Moderate

Excellent

Moderate

Excellent

Grass Intake (kgDM/head/day)

13

15

15.5

17.5

Milk from Grass (litres)

13.0

17.0

18.0

22.0


Forgotten Energy Costs

Two factors which are often overlooked when it comes to calculating expected milk from grass include:

  1. Higher maintenance requirements at grass due to greater energy expenditure. Walking to and from pasture, as well as physically grazing have an energy cost approximately equal to 1-1.5 L/head/day
  2. Additional energy required to remove excess rumen nitrogen due to the oversupply of protein from grass. Milk urea values will be reflective of the amount of excessive nitrogen in the rumen and hence can be used as a guide for estimating associated energy cost, see Table 2.

Table 2: Estimated potential milk loss associated with milk urea values

Milk Urea (mg/dl)

Estimated Milk Loss (Litres/cow/day)

30

0.3

35

0.6

40

0.8

 

Together these two factors can cost the cow energy, equivalent to a loss in potential milk of 1-2.5 L/head/day. This can often account for the differences noted between typical industry recommendations on the milk yield grass is capable of supporting, verses the cow’s realistic performance from grass while maintaining  body condition – the difference between theory and reality often equates to 2L/head/day.

 

Timely Adjustment of Feeding during Wet Weather

Every 3% drop in grass dry matter will reduce grass DMI by 1kg/day. Therefore, pro-active adjustment of feeding on wet days will be essential to maintain performance, see Table 3 for guidance.

Table 3: Impact of weather on grass DMI and additional compound feed required

 

Reduction in grass DMI

Additional Compound Feed Required

Reduce M+ setting in parlour by:

Showery Weather

1 kgDM

1.0 – 1.25 kg/day

2.0 – 2.5 litres

Continuous Rain

2 kgDM

2.0 – 2.25 kg/day

4.0 – 4.5 litres


Managing Milk Butterfat

Maintaining butterfat can be a struggle whilst grazing lush grass, which is high in sugars and oil and low in fibre. To help maintain butterfat:

  • Offer a small quantity of a fibrous buffer feed – Chopped straw, straw pellets, wholecrop etc.
  • Avoid excessive levels of nitrogen fertilizer and maximize days between sowing and grazing
  • Graze at the 3 leaf stage
  • Avoid slug feeding of concentrate in parlour – ideally a maximum of 4 kg/milking
  • Avoid abrupt dietary changes
  • Avoid selective grazing – maintain sward quality. Pre-mowing can help maintain sward uniformity

 

Grazing conditions change quickly so it’s important to walk the grazing platform regularly, gradually increase grass in the diet as soon as growth allows and pro-actively adjust supplementary feed during poor weather. Capitalise on grazed grass but be realistic what you expect grass to support. 

 

by Claire Beckett, Dairy Technical Support Coordinator