Sheep in clover may give you less than you baargained

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Ewes grazing on oestrogenic clovers have low fertility rates because both ovulation and fertilisation rates are reduced.

It is every sheep producers’ worst nightmare. You’ve done everything right (or think you have) but come marking, lambing percentages are horrifyingly low. This was the scenario for Parndana producer Nick Clarke who, in 2012 in his Merino flock, had a 65% lambing percentage and only 35% in his maidens.

“It was a great finish in 2011 and an early start in 2012 so our ewes were in excellent condition and we were expecting to get our usual lambing percentage of around 80%,” Nick said. “When our percentage was so low we spoke to our local vet Deb Lehmann and she organised the abattoir to collect the uteruses from some ewes we had just sold.”

Testing found the ewes had lesions consistent with oestrogenic issues so Deb then collected pasture samples which confirmed the diagnosis – high levels of oestrogenic clovers.

“We knew something was wrong as we heavily hand-feed our sheep so we knew it wasn’t due to poor ewe condition. We checked our rams and they were also healthy so we knew there weren’t any other causes for the low lambing percentage,” Nick said.

Deb said

“The cervix becomes hostile to sperm and cysts can form in the uterus and cervix,” she said. “Permanent infertility can occur if ewes are exposed to oestrogenic clovers over many seasons. Even hay cut from paddocks with toxic oestrogenic levels can retain that potency and can affect fertility if fed to ewes before and during joining.”

Many pastures sown down during the Soldier Settlement days after World War II contained oestrogenic sub clovers, such as Yarloop, Dwalganup and Dinninup. While newer varieties do not have these problems, many properties still have a clover base that contains a high percentage of the older varieties. The older varieties have high levels of hard seed and so can become dominant after a long cropping phase or a run of dry seasons. Nick has since tested the pastures in most of his lambing paddocks.

“The test is quite simple and involves taking a pasture sample and sending it to the lab for analysis,” he said. “We found having this information is crucial in deciding what stock to run in which paddocks with the aim being to keep young ewes away from the worst paddocks.

“I run younger ewes on the lower oestrogenic pastures. We’ve also increased the ram percentage to 3% and ensure rams are in condition score 3. As more ewes will return to service with oestrogen toxicity, the rams have more work to do,” he said.

The other part of the solution is to ‘dilute’ the oestrogenic clovers as much as possible by avoiding any herbicide sprays that will encourage clover dominance.

“We’ve now stopped spray-grazing our pastures. Basically you don’t want to remove other pasture species as they help dilute the oestrogenic clovers,” Nick said.

Since Nick has identified the problem and changed management practices, lambing percentages in the past two years have been well above average at 86% in 2013 and 89% in 2014.

Key tips to improve fertility:

  • do not graze young ewes on pastures that have a high percentage of oestrogenic clovers
  • paddocks with less than 20% clover are likely to be safe
  • delay joining ewes until at least six weeks after the clover was died and ensure they are in condition score 3
  • test pasture hay for oestrogens and if levels are high, only use it after joining
  • aim for 3% rams at joining and check ram health
  • consider culling adult ewes scanned not pregnant as they are likely to be permanently infertile
  • o not spray-top pastures and/or consider drilling in winter feed oat to ‘dilute’ the clover.

Written by Lyn Dohle, Department of Primary Industries and Resources of South Australia. Work supported by the Kangaroo Island Natural Resources Management Board through funding from the Australian Government’s National Landcare Programme.

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