Assessing oestrogenic sub-clover biomass

To assess if the total oestrogenic sub-clover content exceeds 20%, identify and record pasture species along a paddock transect. Use a 1cm thick piece of dowel about 50cm in length with a nail sticking out of each end or with the ends shaved to a sharp point.

In early spring, walk diagonally across a paddock, throwing the stick 50 times at 10-pace intervals. Collect 100 measurements by recording the oestrogenic clover touching each end of the stick. If oestrogenic clover is recorded more than 20 times, sheep grazing that paddock are at risk.

Oestrogen levels of pasture samples can be tested….

Oestrogenic rod assessment

How to manage a paddock if you suspect a problem

  • Manage the stock rotated onto the paddock:
    • don’t graze young ewes or lambs
    • limit grazing by wethers to avoid high exposure
    • rams are not thought to be affected
    • cattle may be affected, but likely this is rare
  • Be aware that high oestrogen levels can be maintained over long periods of time in hay cut from these pastures if dried quickly or used to make silage

  • Ensure soil phosphorus nutrition is adequate as deficiency mayincrease pasture formononetin levels

  • Dilute the proportion of feed intake that contains oestrogens:
    • provide alternative feed sources e.g. shrubs or grasses in adjacent paddocks
    • sow other species into the pasture e.g. rye grass or oats to dilute the intake of sub clover
    • do not grass clean, dilution is part of the solution
  • Remember to consider other reasons for poor lambing percentages.

Pasture renovation – the ultimate solution

To aid success with replacing high oestrogen pastures:

  • reduce clover seed bank by cropping for several years, and prevent sub clover seed set
  • choose a well-adapted, ‘recently released’ low oestrogen cultivar
  • consider a higher seeding rate than normal/recommended to aid the new cultivar to become dominant
  • apply recommended rhizobia at sowing
  • fertilise adequately based on soil tests
  • when renovating pastures ensure certified seed is used to avoid contaminated seed.

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