P.PSH.1171-Phase 2-Maximising the reproductive potential of the meat sheep industry by eliminating high oestrogen clovers, more live lambs on the ground

Summary

Reproductive difficulties in sheep grazing highly oestrogenic subterranean clover (subclover) were described as ‘clover disease’ in the 1940s. By the 1990s, this issue was thought resolved through release of new cultivars. However, there are ongoing reports of poor lambing percentages in Merinos ewes and these can be explained by the persistence of highly oestrogenic cultivars that contain unsafe levels of formononetin in their green leaves.

This project has substantially raised awareness of the continuing issue of highly oestrogenic subclover pastures. This included training to identify oestrogenic cultivars, and on how to remediate the issue in the short and long term, for 975 producers, consultants, veterinarians and students. We also developed an oestrogenic pastures fact sheet and a Ute Guide. Around 600 leaf samples submitted by producers were tested in the re-opened diagnostic centre at the University of Western Australia. Of these, 60% contained higher formononetin than the safe threshold. Dinninup was the most common oestrogenic subclover. Several cultivars released as safe, had a substantial number of samples over the safe limit. Large variation was present in the level of formononetin for individual cultivars, especially Dinninup, the most common oestrogenic subclover identified. It seems that unknown factors are impacting formononetin levels in field samples. We also demonstrated through a field experiment that the soil seedbank of oestrogenic clovers can be very greatly reduced by three years of cropping with in-crop herbicide control of oestrogenic subclover seedlings. We also developed new subclover identification tools to aid the quick identification of oestrogenic subclover contaminants in seed lots.

Objectives

Objective 1

Use a Design Led approach to develop and implement an extension and adoption plan to address oestrogenic induced reproductive failure in meat sheep

One of our project team members undertook a course in Design Led Thinking (DLT) in Brisbane in 2018 at the start of the development of the Phase 2 project. We used DLT to inform our approach to the project.

This may involve but is not limited to:

Five practical farmer workshops per year in association with producer groups and consultants across five states

COVID-19 reduced opportunities to undertake workshops and field days, however, we were still worked closely with producers, consultants and researchers via online technology. These included: The Association for Sheep Husbandry, Excellence, Evaluation and Production (ASHEEP); Department of Primary Industry and Rural Development (DPIRD) in WA; Sheep Connect, Ag KI (Kangaroo Island) and Department of Primary Industries and Regions in South Australia (PIRSA); Perennial Pastures Society (PPS) and Southern Farming Systems(SFS) in Victoria; Local Land Care Services (LLS) and Department of Primary Industries (DPI) in New South Wales (NSW);and the University of Tasmania.

A minimum of four social media releases per year aimed at informing farmers and advisors about the project

We established a Twitter account and connected with southern Australian producers with interest in low Merino lambing rates as our initial contact point. We regularly posted, and producers and consultants used this forum to engage with us directly. Two of our social media posts reached 30,000 potential followers.

Presentations at a minimum of two high-impact industry forums per year (e.g. Agribusiness Update and Livestock Update)

In 2019, we presented at the PPS in Victoria and the ASF committee meeting in Perth. In 2020, we presented online at two annual conferences, Grasslands Society of Southern Australia and PPS. The project leader was the panellist for the webinar hosted by the New South Wales DPI on “Oestrogenic sub clover pastures: identification and potential sheep health issues”.

Objective 2

Implement a monitoring and evaluation plan to record and highlight the results, outcomes and impact of the extension and adoption plan

The extension and adoption relating to the project was highly successful, with 975 people interacting directly. Beyond these numbers, it is difficult to gauge the impact of social and print medias; however, the number of enquiries coming into the team increased with extension over time. The project featured on other media channels such as “The Land”, UWA Institute of Agriculture Annual Reports, PPS newsletter, and “Farming Ahead”.

Objective 3

Use farm consultants to distribute sampling kits to farmers with at least 100 kits returned, clovers identified, and oestrogen levels measured in the laboratory and farmers informed of their result

There was a very enthusiastic response by producers to have their pasture samples identified and analysed for isoflavones. We disseminated 310 free pasture kits with subclover identification sheets to producers; 159 were returned, and many contained multiple paddock samples or samples from several farms (from consultants). All producers received their subclover identification and laboratory results. Of the pasture samples received, 60% had higher formononetin levels in the green leaf than the ‘safe’ threshold (0.2% of leaf dry matter). The most common oestrogenic subclover was Dinninup; its formononetin levels mostly varied from ~ 0.35% to 2.5%, with one outlier at 3%. Some cultivars selected for low formononetin had levels above the safe limit in a significant number of samples, notably Seaton Park and, especially, Trikkala. Enhanced formononetin under waterlogging may be one cause, but further investigation is required. The kits were an excellent strategy to extend our message nationally to the sheep meat and wool industry and increase the awareness of producers, veterinarians and agronomists on oestrogenic subclovers and provide the first real measure across southern Australia.

Objective 4

Produce a Subterranean Clover Cultivar Guide, using photos from Phase 1, covering identification of all common subterranean clover cultivars, including their oestrogen levels, and best alternatives for use in renovating high-oestrogen pastures.

After receiving user responses, the feedback from the livestock and seed industries was a preference for an oestrogenic subclover Ute Guide rather than an updated Subterranean Clover Cultivar Guide; hence, we focused on producing a Ute Guide, which will be released in late 2021.

Objective 5

Update yearly a handout, targeted at farmers and advisors, outlining the problem (in terms of clinical and subclinical impact on livestock), how to identify it, and how to mitigate it using pasture renovation

We produced two oestrogenic subclover fact sheets for the sheep meat and wool industry. The UWA version was later updated by MLA and is available on their website. (P.PSH.1171) - here

Objective 6

Communicate to seed industry about oestrogenic clovers

There is an unintentional inflow of oestrogenic subclover cultivars onto farms due to the sowing of non-certified commercial seed. In 2020, we discussed the issue with the ASF and the need to undertake testing for oestrogenic subclover contaminants in commercial seed. They agreed to highlight the issue nationally. They will also encourage customers to buy certified subclover seed.

Objective 7

Complete case study of a high-oestrogen pasture renovation

At the UWA Ridgefield Future Farm, on a medium rainfall site (winter dominant, annual average 425 mm), we reduced the oestrogenic soil seed bank on a commercial scale under continuous cropping (with in-crop control of broadleaf weeds and subclover seedlings) over three years from an estimated 220 kg/ha to just 9 kg/ha by the end of March 2021. Further research is needed to identify economic options for renovating oestrogenic pastures, especially where large seedbanks of oestrogenic subclover exist and where cropping options are limited, such as in higher rainfall zones or permanent pastures that cannot be cropped due to frequent rocks, trees or waterlogging.

Objective 8

Quantification of clinical and subclinical cost of oestrogenic clovers for livestock

Our cost-benefit analysis estimated the impact of remediating oestrogenic pasture—to achieve 10% more lambs and 1% less ewe mortality—on overall farm profit. The potential effect of ‘clover disease’ expressed as a decline in lambing percentage ranged from $10–51 per hectare per year of gross margins per 10% change in lambing percentage.

Key findings

The project has substantially raised awareness of the continuing issues of highly oestrogenic subclovers in 975 producers, consultants, veterinarians and students. This included training to identify oestrogenic cultivars and how to remediate the issue in the short and long term; many more were alerted to the need to monitor their pastures through social media.

Around 600 leaf samples submitted by producers were tested in the re-opened isoflavone diagnostic centre at UWA. All producers received their pasture identification and laboratory results, demonstrating the extent of highly oestrogenic subclover pastures across southern Australia. The kits were an excellent strategy to extend information on oestrogenic subclovers nationally to the sheep meat and wool industry.

Of the subclover samples submitted, 60% contained higher formononetin than the safe threshold of 0.2% of green leaf tissue. Dinninup was the most common oestrogenic subclover these samples. Several cultivars released as safe, notably Trikkala, had a substantial number of samples over the safe limit. Large variation was present in the level of all isoflavones, including formononetin for individual cultivars, especially Dinninup.

A contributing factor to safe cultivars being over the limit and high variation in formononetin is likely waterlogging. There was no evidence of suboptimal nutrition being a factor, although previous research suggests it is possible. Thus, it seems that unknown factors are impacting formononetin levels in field samples. Screening of new cultivars for formononetin levels under commercially relevant field conditions is therefore highly recommended.

The soil seedbank of oestrogenic clovers can be very greatly reduced by three years of cropping with in-crop herbicide control of oestrogenic subclover seedlings. Sowing of a low-formononetin cultivar directly following an oestrogenic pasture is likely to result in considerable oestrogenic subclover contaminating the pasture in.

Benefits to industry

The project alerted producers, consultants and researchers across southern Australia to the problem of oestrogenic subclovers through workshops, laboratory results, identification tools, presentations, pasture walks and social media. Thus, the sheep meat and wool industry is now much more informed about ‘clover disease’. Future extension will be aided by: the oestrogenic subclover factsheet; the oestrogenic subclover Ute Guide; the map of southern Australia indicating where clusters of oestrogenic subclover are present.

The sample kits enabled many producers to be informed about the presence of oestrogenic subclover in their pasture and identified the cultivars present. The results suggested a significant proportion of pastures across southern Australia likely contain oestrogenic subclover and that Dinninup is the most common cultivar that producers need to know how to identify.

We communicated with producers, and the pasture seed industry, about the need to renovate with certified seed and developed a method to identify and visually separate seedlings of the highly oestrogenic Dwalganup from Dalkeith: this should reduce the inflow of oestrogenic subclover into the system.

We demonstrated that the soil seedbank of oestrogenic clovers can be very greatly reduced by three years of cropping with in-crop herbicide control of oestrogenic subclover seedlings. Our techniques will guide producers to renovate successfully.

Future research

A more comprehensive field survey of New South Wales is needed to better under the occurrence of oestrogenic subclover.

Further information is required to determine which environmental and management factors can cause the level of formononetin in subclover to increase in pastures under field conditions.

Further economic modelling analysis should be undertaken to compare the full costs and benefits that result from pasture improvement by renovating with new cultivars.

Research is needed to develop an accurate in-field test for pasture formononetin level. If successful, the need to identify subclovers visually or submit pasture samples to a laboratory will be removed and producers will be able to quickly act to address the issue by, for example, removing livestock from the pasture or strategic grazing.

Research is also needed to develop a simple in-field test to be used by livestock veterinarians to determine equol levels in sheep grazing oestrogenic subclover.

Development of an herbicide-resistant subclover is urgently needed in the medium and high rainfall zones where producers cannot crop due to waterlogging and thereby reduce the soil seedbank of oestrogenic subclovers.