Brand: MAGNUM ® IGR Pour-on


FORMULATION: «pour-on» for topical administration.

ACTIVE INGREDIENT(S)diflubenzuron 25 g/L (= 2.5%)

CHEMICAL CLASS of the active ingredient(s): insect growth regulator (= IGR, benzoylphenyl urea)


PARASITES CONTROLLED* (spectrum of activity)

* Country-specific differences may apply: read the product label.


  • Control and treatment of body lice Bovicola (Damalinia) ovis on sheep off-shears and unshorn lambs up to 3 months of age.  
  • Protects against the establishment of lice populations for up to 12 weeks.
  • Aids in the control of body lice infestations in long woolled sheep.

New Zealand

  • Also for protection against blowfly strike (incl. Lucilia cuprina) for up to 8 weeks.


* Read the product label for further details on dosing and administration.

Use recommendations, off-shears, Australia: approved only for body lice control, not for flystrike prevention.

Sheep weight (kg) Dose rate (mL)
<10 8
11 - 20 10
21 - 30 15
31 - 55 20
56 - 75 25

Use recommendations New Zealand:

  • Flystrike control:
    • Lambs at docking and for prevention of crutch strike: apply around he crutch area (17 mL)
    • Sheep >35 kg apply around he crutch area (17 mL) and in a single strip along the backline from between the ears to the tail (17 mL): Total 34 mL.
    • Sheep >35 kg: apply around he crutch area (17 mL) and in a single or double strip (2x 17 mL) along the backline from between the ears to the tail (17 mL): Total 51 mL.
  • Lice control: on strong-wool type breeds up to three months off-shears and Merino type breeds off-shears only (machine shorn) at the following dose:
Sheep weight (kg) Dose rate (mL)
15 - 20 12
21 - 30 15
31 - 55 20
56 - 75 25
>75 5 mL/10 kg

Read the product label for further details on dosing and administration.


  • LD50 (acute oral) in rats: >5000 mg/kg
  • LD50 (acute dermal) in rats: >5000 mg/kg
  • Estimated hazard class of the a.i. according to the WHO classification of pesticides: U, unlikely to present acute hazard in normal use.

Withholding periods (=withdrawal times) for meat, milk & shearing (country-specific differences may apply: read the product label)

  • Meat:
    • Australia: used off-shears: NIL; Used on wool ≥6 weeks & <6 months: 42 days. ESI: used off-shears NIL; used on long wool 42 days.
    • New Zealand: NIL.
  • Milk for human consumption:
    • Australia: Not approved in Australia.
    • New Zealand: Milk intended for sale for human consumption must be discarded during treatment and for not less than 35 days following the last treatment.
  • Shearing:
    • Australia: 6 months.
    • New Zealand: 2 months.

You may be interested in the following articles in this site dealing with the general safety of veterinary products:


Risk of resistance? YES. Resistance of body lice reported in Australia and New Zealand in field populations. Resistance of blowfliy strike widespread in Australia and New Zealand

Resistance of body lice Bovicola (Damalinia) ovis to diflubenzuron and other benzoylphenyl ureas has been reported in Australia and New zealand and it must be expected to increase. For this reason efficacy of this product against sheep body lice may not achieve the label claims. The same is true for flytrike in New zealand.

This means that if this product does not achieve the expected efficacy against the mentioned parasites, it may be due to resistance and not to incorrect use, which is usually the most frequent cause of product failure.

Alternative chemical classes/active ingredients for product rotation to prevent resistance of body lice to triflumuron:

These alternative products may not be available in all countries, or may not be available as pour-ons.

Learn more about resistance and how it develops.


Are the active ingredients of this product ORIGINAL* or GENERICS**?


*Meaning that they are still patent protected and generics are not yet available
**Meaning that they have lost patent protection and may be acquired from manufacturers of generic active ingredients other than the holder of the original patent.

COUNTRIES where this brand/product is marketed: Australia, New Zealand
GENERIC BRANDS available? YES, a few ones.

Click here to learn more about GENERIC vs. ORIGINAL drugs.

For an overview on the most used antiparasitic pour-on brands click here.


MAGNUM IGR Pour-on Sheep Lice Destroyer is a lousicide from COOPERS (MERCK AH - INTERVET) containing generic diflubenzuron.

Diflubenzuron is a veteran IGR, the first benzoylphenyl urea discovered already in the 1970s (by PHILIPS-DUPHAR). It is scarcely used in livestock and agriculture, but not in pets. It was introduced for use as a lousicide in sheep in Australia only in the 1990's (under the TM FLEECARE from HOECHST), when lice developed high resistance to synthetic pyrethroids, which lost approval for lice control. Diflubenzuron and other benzoylphenyl ureas subsequently conquered the sheep body lice market very quickly in Australia after resistance to synthetic pyrethroids exploded and organophosphates that still worked well were progressively withdrawn for safety reasons.

It is important to understand that this and other products containing insect growth regulators do not kill adult lice that may infect sheep or cattle at the time of treatment, i.e. they don't have a knock-down effect. What they do is to prevent development of immature stages. Larvae and/or nymphs fail to molt to the next stage and die. Therefore they are used to prevent the further development of immature stages or eggs of occasional adult lice that sheep may catch.

It is interesting to know that neither diflubenzuron nor other benzoylphenyl ureas are used on sheep in the EU, the US or in Latin America, where body lice is also an important pest of sheep, and flytrike also in the UK, Ireland and the Netherlands. The likely reason is that organophosphates and/or synthetic pyrethroids are still widely used in these countries against these pests that have not yet become resistant to these chemicals there.


This article IS NOT A PRODUCT LABEL. It offers complementary information that may be useful to veterinary professionals and users that are not familiar with veterinary antiparasitics. 

Information offered in this article has been extracted from publications issued by manufacturers, government agencies (e.g. EMEA, FDA, USDA, etc.) or in the scientific literature. No guarantee is given on its accuracy, integrity, sufficiency, actuality and opportunity, and any liability is denied. Read the site's DISCLAIMER.

In case of doubt contact the manufacturer or a veterinary professional.