Learn to identify clover varieties and safeguard sheep fertility

Clover disease in sheep is caused by old cultivars of subterranean clover high in oestrogenic compounds. These compounds can cause a range of issues in livestock which include a permanent form of infertility, or a temporary form just before or and the time of mating. Both of these forms continue to reduce reproductive potential and profits in the sheep meat and wool sectors, although profits from the wool section are less affected due to less reliance on reproduction. Dr Foster stated: "The literature from the 1970-1990s and our own preliminary data suggest that clover disease persists in production systems and is likely a significant contributor to suboptimal lambing rates. Paddocks that are dominated by oestrogenic clover may lead to permanent reproductive decline in ewes, with impacts including prolapsed uterus, stillbirth, masculinised genitals in the ewe and false bladder and abnormalities in wethers". However, Dr Foster points out that the classic signs of oestrogenic sub-clover impact, like uterine prolapse and lactating wethers may not be as common as they were 60 years ago.

In spite of this persistent problem it seems that following the release of safer subclover cultivars by the late 1990s, many producers and consultants considered the problem to be in the past. Indeed, the last comprehensive survey of oestrogenic subclovers across the Mediterranean climate of the southern states was in 1979 in South Australia. However, recent producer surveys across southern Australia by the UWA team reveal this is not the case. Indeed, it was found that around 20 % of all pastures may contain significant amounts of high-oestrogenic clover cultivars, such as Dinninup, Geraldton, Dwalganup, Tallarook and Yarloop: in some districts up to 65 % of paddocks were affected. Pastures with greater than 20 % of biomass consisting of oestrogenic clover are regarded as unsafe and should be avoided by most classes of livestock with careful management or renovation then considered. However, the UWA team also found that even when paddocks had been oversown or renovated with new improved cultivars, the older oestrogenic cultivars had often persisted due to factors such as being hard seeded, already having a large seed bank and being very competitive. Indeed, if a paddock had not been resown successfully to a newer cultivar in last 25 years, the probability of containing some oestrogenic clover was high.

Successful renovation of a paddock containing oestrogenic clovers with newer cultivars should involve oversowing with certified clover seed at a high rate, using new rhizobia and/or dilution of the oestrogenic clover component of the pasture with oats or grasses to reduce animal intake. Pastures with very high levels of oestrogenic clovers may need to be cropped (e.g. with oats) for several years to reduce the seed bank; although this may be difficult in wet places, which favours the oestrogenic Yarloop. Note also that uncertified seed should be tested to avoid accidently introducing oestrogen clover again. Indeed, Dr Foster found 5 out of 13 non-certified seed lines contained 20 % or more of oestrogenic clover seed. Overall, Dr Foster said renovating high oestrogenic pastures would lead to more lambs per ewe joined, less mortality and a longer reproductive life in ewes.

If producers need paddocks with oestrogenic clover for grazing then Dr Foster recommends that soil tests be undertaken and any deficiencies remediated, as low levels of phosphorus and sulphur can result in a two or three fold increase in oestrogenic compounds in the green leaves of subclover. He also recommended grazing only after joining or after the subclover is dry for 6 weeks. He also suggested producers limit exposure by younger ewes to maximise their reproductive life. At the enterprise level, producers could also switch to more wool production, retaining more wethers, although the impact of doing so on profits would require consideration.

Several other worrying issues were flagged by Dr Foster. "The issue of hay and silage is a bit of a sleeper as few know about danger of oestrogenic clovers in the field," said Dr Foster. "And virtually no one knows about the risk of hay and silage cut from these clovers and the potential impacts on livestock fertility." For instance, he noted that for producers buying in feed, as did most during the drought, there is the real chance of importing untested oestrogenic clover hay, which can retain the potency when dried quickly or made into silage.

Dr Foster also noted that while cattle may not be as affected by oestrogenic pastures or hay as sheep, there may still an impact; indeed an impact has even been noted for captive cheetahs and rhinoceros when fed a diet containing oestrogenic feed. Cattle on silage containing oestrogenic clovers may have a temporary reproductive set-back, as has been found for shed fed cattle in Europe and Norway.

"The cattle issue is an area we need to investigate further and soon. I am suspicious that cattle are not immune to the effects of high oestrogenic clover. It has previously been thought that rams are protected partially or even fully, but even that is now under question now; there is no information on impact on bulls. There is a clear need for an Australian-relevant investigation and new guidelines on which to make livestock recommendations around oestrogenic pastures and cattle".

Dr Foster concluded: "The good news is that we have just appointed a new Lefroy Postdoctoral Fellow at UWA. Ms Kelsey Pool will work with Dr Dominique Blache and the rest of the UWA team with an initial focus on investigating the effects of oestrogenic compounds on ram reproductive function. We are hopeful of generating preliminary results to share by the first half of next year. Overall, the UWA team aims to benefit producers and industry by redefining understanding of clover disease".

If you think you have a problem sheep or cattle grazing oestrogenic clovers please contact Dr Foster at the University of Western Australia at kevin.foster@uwa.edu.au. Dr Foster has a limited number of free oestrogenic pasture test kits to distribute; results will inform you of the cultivars present in your pasture and their level of osteogenic compounds.