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Mating sheep on red clover swards

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The research

Four farmers and researchers are investigating whether the inclusion of red clover in swards impacts the fertility of grazing ewes.

Red clover is increasingly being recognized for its multiple benefits and ecosystem services. It is also a component of sward mixes for countryside stewardship payments. Some farmers are hesitant to put down to herbal leys containing red clover, potentially limiting yield; drought resilience, on-farm biodiversity. This is because farmers and advisers rely on outdated research from the 1960s and 1970s which established that grazing ewes on red clover reduced their fertility. This research has been used as the basis of veterinary advice since, yet is limited in its applicability as it was done in the southern hemisphere on pure red clover swards rather than as part of a mixed sward, whereas red clover is rarely grown as a monoculture in the UK.

Red clover contains phyto-oestrogens which mimic oestrogen and interfere with the fertility of sheep. Modern varieties of red clover have been developed with lower levels of phyto-oestrogens, yet no practical research has been conducted to establish whether these new varieties are ‘safe’ to graze during mating. Anecdotal evidence from farmers suggests that grazing multi species grassland swards containing red clover (comprising 10-30% of the sward) does not negatively affect fertility.

If no negative effect on ewe fertility is found, the potential economic and environmental benefits are huge. Sheep farmers could confidently integrate red clover into more of their grazing swards and thereby drive down input costs, reduce their carbon footprint and improve sustainability. It would also enable more businesses to establish legume and herb rich swards as part of agri-environment schemes and therefore generate additional sources of income.



The benefits

Red clover is becoming increasingly popular for a variety of reasons. It is a crucial component of the GS4 mix (legume and herb-rich swards) - one of the most popular stewardship options for arable or grassland farmers, where a minimum of 10% red clover coverage is required. Red clover's benefits include:

- High yielding
- Drought resilient
- Nitrogen fixer - reduces use of inorganic nitrogen
- High protein content
- Nectar rich (for pollinators) - in GS4 mix, the sward has to be left to rest for 5 weeks in the summer to assist pollination

Within herbal ley mixes, in the autumn, which is also mating season, red clover is more prevalent than other species in the mix. Farmers require confidence to graze breeding stock onto clover during this time and are otherwise limited on how much land they can put down to multi-species swards containing red clover. If no negative effect on ewe fertility is found, farmers could expand how much land is put down to legume and herb rich swards, which would generate additional sources of income and boost farm sustainability.

Trial design

Four farmers across the West Midlands and Wales are triallists in this field lab. All of them have a flock of min 100 breeding ewes, randomly split 50/50 into two 'sub-flocks', taking account of variation in age, breed and past performance. One sub flock will graze the sward containing red clover for at least 3 weeks pre mating and for the duration of the mating period. The control sub-flock will be grazed on swards which do not contain red clover.

At the end of the mating period the sub-flocks will be merged (if possible) to ensure management for the remainder of the ewe’s pregnancy is the same. Scanning results will be collated to determine an overall trend.

Information on fields and swards in the field lab will be collected during the trial set-up, including soil type, establishment date, seed mixture and varieties sown. During the set-up visit previous fertility performance data and details of normal grazing policy will also be gathered. 

During the field lab the quantity of red clover in the sward will be assessed using quadrats to establish the percentage of red clover contained within the sward prior to and during the grazing period. 3 weeks before the start of the mating season, a sample of the sward will sent for lab analysis for dry matter and nutritional content. 

The farmers will record treatment of the sward, stocking rate, length of time grazed prior to tupping and to record the scanning results for each sub flock separately.  

Once the field lab trial is complete the results will be collated and analysed to determine if mating sheep on red clover swards influences fertility.

We started off with just 20 acres using red clover and have gradually increased it over the years, which has helped us to decrease our dependency on nitrogen. Without the legumes we would be looking at paying huge costs this year – we would have gone from £35,000 last year to £90,000 this year.

A portrait of Marc Jones.

Marc Jones, Sheep Farmer & Farm Consultant, Trefnant Hall Farm

Latest updates

Following the successful result of the field lab, ADAS is conducting a follow-on survey to better understand what barriers remain to using red clover mixed leys. The results will help identify how to encourage greater take-up of red clover by the industry.

The survey takes five minutes to complete and all sheep farmers across the UK are invited to take part. Responses submitted by 31 July 2023 will be entered into a prize draw to win a hamper worth £100.

Click here to take the red clover survey.

If you wish to find out more or get more involved, please email redclover@adas.co.uk

Kick off meeting
Farm set ups confirmed
Pre-tupping sward assessments
End of mating period, sward assessments
Ewes scanned & recorded for fertility
Analysis & results
Results meeting & final report published

Group Coordinator

A portrait of Gillian Preece.
Gillian Preece


South Shropshire

Gillian is a senior agricultural consultant at ADAS and also a first-generation sheep farmer in Shropshire. She is an experienced consultant who has worked in the livestock sector throughout her 25 years in the industry. She works predominantly with beef, sheep and dairy farmers assisting them with business management, technical aspects of livestock production and accessing environmental schemes. As a partner in their own farm business Gillian also has practical experience of beef and sheep farming, alongside her husband Phil.


A portrait of Marc Jones.
Marc Jones

Trefnant Hall Farm


A portrait of Gillian Preece.
Gillian Preece


South Shropshire


  • Ewes that grazed leys containing red clover had a higher scanning percentage than ewes that grazed non-red clover leys
  • There was no negative effect on ewe fertility at 3 of the 4 sites
  • It is thought that the groups of breeding ewes which grazed the red clover swards achieved a higher scanning percentage due to improved availability and quality of forage before and during the mating period

This should increase farmers' confidence in integrating red clover into grazing swards, which in turn would reduce input costs and reduce farm carbon footprint. These findings may also encourage more businesses to establish legume and herb-rich swards as part of agri-environment schemes to generate additional income.

Further work will be necessary to determine whether there is an upper limit to the proportion of red clover. The red clover fresh weight content of the herbal leys in this study ranged from 8.9% to 36.9% producing an average of 17.6%, despite the seed mixes all originally containing 10% red clover by weight. Further research should also be performed to determine the best way to conserve red clover content in swards in livestock grazing systems, as well as reintroducing or stitching in red clover without ploughing.