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Do herbal leys affect milk yield and quality?

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Establishing diverse swards can improve the resilience of grazing platforms. However, the un-quantified effect of increased sward diversity on milk yield and quality is a potential financial risk for dairy farmers. This effect on milk has not been trialled and recorded in the UK before.

In this Farm Net Zero field lab two farmers will monitor the difference between milk produced by cows grazing a rye grass sward, and cows grazing a herbal ley / diverse sward.

Alongside the trial a discussion group of Cornish farmers will explore the benefits of their own herbal leys, and follow the trial results.

The idea for this field lab arose from the Farm Net Zero project discussion groups, and it is part of the Farm Net Zero Project in Cornwall, funded by the National Lottery Community Fund.

The research is being led by Dr Daniel Enriquez Hidalgo of Bristol Veterinary School, with assistance form Cornwall Wildlife Trust and Trifolium Services.

The benefits

There are many accepted benefits of growing herbal leys, they can:

  • Improve soil structure and health
  • Provide resilience in dry periods
  • Extend the grazing season
  • Benefit carbon sequestration
  • Nitrogen fixation from legume species – so requires little fertiliser
  • Improve livestock growth rates when rotationally grazed
  • Improve biodiversity of bird and insect species
  • Some species have anthelmintic properties – so less need for wormers

However, there has never been a study in the UK looking directly at the impacts of herbal leys on milk for dairy farmers.  This field lab aims to look at the impacts.

Trial design

Andrew Brewer, who farms in Cornwall, will monitor milk throughout the grazing season. A second farm will take part in the late summer / autumn after calving.

The dairy herd on each farm will be split into two groups; one will be grazed on a standard rye grass-clover ley.  The rest of the herd will be grazed on herbal leys.   The milk yield and main constituents will be regularly monitored from each group.  The forage will be sampled and analysed monthly throughout the growing season to get an idea of which species are dominating.

The trial will last for one year.

Latest updates

Conor from Cornwall Wildlife Trust braved the driving Cornish rain to collect the April forage samples this week.  


Weighing forage samples at the Eden Project.

The trial cows have now been split into their groups, with half grazing ryegrass and the others grazing diverse swards.  

The trial cows will be moved onto the sampled areas immediately after sampling.  The milk yield will be recorded tomorrow, and the milk sampled for constituents, including butterfat and protein. This should give us a picture of the impact forage type has on milk.  This will be repeated monthly throughout the grazing season until roughly November.


The first forage sampling was carried out today at the trial farm. Conor Kendrew at Cornwall Wildlife Trust collected samples from both the diverse swards and the ryegrass swards that the cows will be grazing tomorrow and over the next few days.  Forage samples will be taken monthly by the group to get a good understanding of what species are growing in the fields which the two groups of cows will be grazing.  

Conor Kendrew at Cornwall Wildlife Trust checks out the grass in the trial fields

Wet weather has delayed grazing plans this year, so Andrew Brewer, the farmer, has been unable to split the cows into their trial groups yet.  Let's hope it dries up soon.


Jan 24

Trial begins when cows start grazing outside

Mar 24

Discussion group meet to look at first set of results

Jun 24

Second farmer joins trials

Aug 24

Trial ends when cows go inside for the winter

Nov 24

Results and report

Jan 25

Group Coordinator

A portrait of Laura Gude.
Laura Gude

Soil Association

Bristol / South West

As the Innovative Farmers Network Coordinator, Laura engages with farmers, scientists, industry bodies and advisors to launch on-farm trials, ensure they keep running smoothly, and to share results. With an MSc in Sustainable Rural Development, Laura trained as a land agent. She then worked as a farming advisor in Devon, particularly on projects aimed at reducing diffuse water pollution in river catchments.


A silhouette of an unidentifiable person.
Andrew Brewer



A portrait of Dr Daniel Enriquez Hidalgo.
Dr Daniel Enriquez Hidalgo

University of Bristol


A portrait of Cornwall Wildlife Trust.
Cornwall Wildlife Trust


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