Understanding DDE Downgrades

Summary:

Here you’ll find an overview of what DDE is, how it gets into milk, and practical ways to manage and reduce DDE residue risk on farm.

DDT is a synthetic organochlorine pesticide that was applied extensively to pastures in the 1960s and 1970s to control grass grub.

As DDT is extremely fat-soluble, it accumulates in animal fat, including milk. DDE is the only DDT metabolite that is expressed in milk.

Downgrade support

Downgrade levels are set at 0.3 mg/kg milk fat from 1 June to 30 September and 0.5 mg/kg milk fat from 1 October to 31 May to meet industry milk quality targets.

See the Fonterra Farmers’ Terms of Supply for more information about DDE levels, testing requirements and downgrades that you will incur if you supply milk with unacceptable DDE levels.

Organise a traceback

Your milk quality results are available daily on your tanker docket or on the Farm Source website. If you have any questions about these results or managing DDE residue on your farm, call the Farm Source Service Centre on 0800 65 65 68.

In some situations, the DDT levels present in soil on the milking platform may be so high that you require specialised management. Fonterra has expert help available for such situations. Contact the Farm Source Service Centre on 0800 65 65 68 if you think this situation applies to you.

A snapshot of what to look for:

  • DDE levels usually peak in the first six weeks of lactation as cows lose body condition.
  • The highest DDE levels occur in early lactation as stored residues are released after the dry period.
  • Milk DDE levels can rise when cows lose condition or graze paddocks with DDT residues.
  • DDE levels in milk after calving depend on the amount stored in body fat at calving.
  • Body fat DDE levels at calving are influenced by DDE levels at drying off.
  • Intake of DDT over winter affects the amount of DDE stored in the cow.
  • The cow’s body condition score at calving also impacts DDE levels in milk.

Management can reduce the levels of DDE in milk

Research undertaken in 1989, 1990 and 1991 by the Ministry of Agriculture and Forestry has shown that management can greatly reduce the levels of DDE in milk.
  • Better cow condition at drying off reduces DDE concentration stored in body fat.
  • Increasing cow condition in autumn lowers DDE levels and improves milk solids production.
  • Testing soil DDT levels across all grazing paddocks is essential for managing risk.
  • High soil DDT levels (above 0.5 ppm) increase the risk of elevated spring milk DDE levels.
  • Milk DDE levels are typically lowest between October and January (base period).
  • Grazing cows or young stock on off-farm land can impact spring DDE levels.
  • Low-DDT grazing areas during winter help reduce DDE levels at calving.
  • Weight gain during the dry period on low-DDT soils is critical to reducing DDE risk.
  • Farms with high soil DDT levels can still be managed successfully with the right practices.

Prevention best practice

The following summarises the most important best practice steps for helping to reduce milk DDE levels:
  • Winter graze cows on soils with the lowest possible DDT levels
  • Knowing the amount of DDT at a paddock level gives you the best information to manage your levels of DDE. 
    • The level of DDT in soils can be highly variable across a single block of land. 
    • Because of this Fonterra recommends soil testing be completed by an approved tester. 
    • You can contact Fonterra for an updated list of approved DDT soil testers in your region. 
    • Take a test or request results if sending cows to grazing
  • Calve your cows in good condition by:
    • Drying off at BCS 4.5. or better
    • Put condition on in winter by feeding well
  • Graze replacements on low or nil DDT soils
  • Select a low DDT property when purchasing/leasing additional land for milking on or using as a grazing block
  • Grow green feed crops on low DDT residue soils. No root crops unless DDT is very low (0.1. mg/kg soil or less)
  • Develop a good relationship with your grazier and manage your grazing
  • Avoid your highest DDT paddocks at calving and drying off
  • Priority graze early calving cows and young low condition cows on your lowest winter DDT grazing. Lower priority can be given to older and late calving cows.