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Beyond the Bale : March 2019
ON FARM 55 Some older sub clover cultivars that were widely sown in Australia from the 1930s to 1980s have high levels of oestrogenic compounds. These can cause a number of reproductive disorders in ewes and together form ‘clover disease’. While newer varieties do not have this problem, remnant populations of the older sub clovers could still potentially impact sheep production. Clover disease affects ewes and wethers. Symptoms include: lowered ewe fertility, increased difficult births, prolapse of the uterus, udder development and milk secretion in nonpregnant ewes and wethers, and enlarged bulbourethral glands and urethral blockages in wethers. Clover disease will only impact sheep when high oestrogenic clovers make up 20 per cent of the pasture eaten by sheep. Temporary infertility can occur where ewes graze germinating or green oestrogenic clover at mating or six weeks before mating. Permanent infertility occurs when ewes graze oestrogenic pastures for two or three years. Sheep are most at risk while grazing when the leaf material is still green, rather than dry pasture. However if very good clover hay is made from the oestrogenic clovers and the leaf material is cured very well and has kept its colour, such hay can still be oestrogenic. Although the older oestrogenic (‘bad’) sub clovers have not been planted for many years, like all sub clovers they produce a percentage of hard seed that can survive Sheep producers are being urged to check their clover pastures for older high-oestrogenic sub clover varieties that can cause infertility in sheep and low lambing percentages. false breaks and dry springs and therefore persist in many paddocks. Regeneration might occur following cropping rotations or drought conditions. If one of your pasture recovery strategies following the drought is to increase the sub clover population by using the existing clover plants then you should check that they are not oestrogenic cultivars. IMPORTANT TO CHECK YOUR CLOVER PASTURES Not all older cultivars are high in oestrogens; the main bad cultivars of concern are Dwalganup, Dinninup, Yarloop and Geraldton. To identify the bad cultivars three parts of the plant need to be examined: the leaf markings, the hairiness of the runner (not the leaf stalk) and the colour of the calyx below the petals in the flower. Unfortunately, it can be very difficult for farmers and agronomists to accurately identify sub clover cultivars, but ‘Good Clover Bad Clover’ fact sheets to help in identifying bad clover are available on the website of AWI’s state grower network Sheep Connect South Australia (see below). Primary Industries and Regions SA (PIRSA) is helping increase producer awareness of potential issues and management strategies through a new Good Clover Bad Clover project, which is an MLA Producer Demonstration Site project supported with co-funding from Sheep Connect South Australia, the MacKillop Farm Management Group and Natural Resources South East. PIRSA’s David Woodard says 160 producers were surveyed as part of the project with the majority unaware of the presence of oestrogenic clover and not confident in identifying such clovers. “Some 85 per cent of producers had never undertaken visual or laboratory analysis of their paddocks. Since, visual assessment and laboratory tests have been undertaken from 25 paddocks across 10 focus farms in south east SA and Kangaroo Island,” he said. “Of the 25 paddocks, 20 paddocks had greater than 20 per cent oestrogenic clover present in the clover portion of the paddock. Of the 20 paddocks, 50 per cent had the potential to cause fertility issues in ewes with visual assessments ranking them moderate to high.” WHAT IF I HAVE BAD CLOVER ON MY FARM? Once oestrogenic cultivars have been identified, the next step is to determine how potent the pasture may be to sheep. This will vary with the pasture composition across the paddock. Other good cultivars low in oestrogen and other pasture grasses and broadleaf plants will collectively dilute the amount of oestrogens that the sheep will consume. Paddocks can be assessed by one of two methods: visually by the ‘Stick method’ or by collecting clover samples and sending them for laboratory analysis of oestrogen levels. Both methods are described in the Good Clover Bad Clover fact sheets. The safest pastures should be reserved for ewe weaners and maiden ewes; the mid-aged breeding ewes on the next safest and so on. The higher oestrogen ranked paddocks should be kept for older breeding ewes, steers, lambs destined for slaughter, wethers or cropped. These higher ranked paddocks could be also targeted for pasture renovation with more suitable low oestrogen cultivars of clover – seek advice from your local agronomist. It is important to examine overall ewe management as a number of factors can attribute to poor lambing performance. These include inadequate nutrition of ewes at mating, poor ram fertility, over feeding in late pregnancy, and other general health problems which can overshadow the effects of grazing oestrogenic pastures. Consult your veterinarian if you have any problems. MORE INFORMATION: Good Clover Bad Clover fact sheets on www.sheepconnectsa.com.au/factsheets KEY POINTS: • Clovers containing oestrogens can significantly impact on lambing percentages. • Know the 4 ‘bad’ clovers: Dwalganup, Dinninup, Yarloop and Geraldton. • Rank your pastures. • Graze toxic paddocks selectively or implement strategies to eliminate the bad clovers. CHECK YOUR CLOVER PASTURES!
In the Shops - March 2019