Brand: EUREKA GOLD ™ OP Off-Shears Spray-on

Company: COOPERS

FORMULATION: concentrate for topical administration as a «spray-on»

ACTIVE INGREDIENT(S)Diazinon (= dimpylate): 9.33% = 93.3 g/L

CHEMICAL CLASS of the active ingredient(s): Organophosphate


PARASITES CONTROLLED (spectrum of activity)

  • Control of body lice Bovicola (Damalinia) ovis on shorn sheep within 24 houres after shearing.  


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

This product must be diluted before use:

Product (litres) Clean Water (litres) Ready-to-use diluted product (litres) Number of 50 kg sheep treated
1 6 7 46
5 30 35 233
10 60 70 466
20 120 140 933

Dilution rate: 1:6 equivalent to 13328 mg/L = ppm = parts per million

Dose rates using the diluted product:

Sheep weight (kg) Dose rate (mL) Critical Comments
6 - 10 30 1. Apply a single wide band from the neck just behind the ears to the butt of the tail.2. Use only the recommended applicator.
11 - 20 60
21 - 30 90
31 - 40 120
41 - 50 150
51 - 60 180
61 - 70 210
71 - 75 225
> 75 2 mL/kg


  • LD50 (acute oral) in rats: for the a.i. 300-400 mg/kg
  • LD50 (acute dermal) in rats: for the a.i. 360 mg/kg
  • Estimated hazard class according to the WHO: III, slightly hazardous.

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

  • Meat: Australia 21 days (ESI 21 days)
  • Milk for human consumption: Not approved in Australia.
  • Wool: Australia: 2 months.

WARNING !!!: Never use on humans, dogs or cats.

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


Risk of resistance? LOW. Resistance of sheep body lice to diazinon and other organophosphates is rather unsusual in Australia after the many years of intensive use of synthetic pyrethroids and benzoylphenyl ureas (a particular group of insect growth regulators). It has been also shown that body lice populations highly resistant to synthetic pyrethroids are particularly susceptible to organophosphates.

This means that if this product does not achieve the expected efficacy against the mentioned parasites, it is likely to be due to incorrect use rather than to a resistance problem. Incorrect use is usually the most frequent cause of product failure.

However, uninterrupted use of diazinon or other organophosphates against sheep body lice for years is likely to result in resistant lice. For this reason rotation with other chemical classes is highly recommended.

Alternative chemical classes/active ingredients for product rotation to prevent resistance of body lice to diazinon or other organophosphates:

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.
GENERIC BRANDS available? YES, but rather few. EUREKA GOLD OP is itself a brand containing generic diazinon.

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

Click here for an overview on the most used antiparasitic BRANDS with concentrates for dipping, spraying, or jetting.


EUREKA GOLD OP from COOPERS is one of the few organophosphate products still approved for use on sheep in Australia. It is also one of the few spray-ons that is not sold as a ready-to-use formulation but as a concentrate that must be diluted before administration.

Diazinon (also called dimpylate) is a veteran broad-spectrum organophosphate introduced in the 1950s by GEIGY (later CIBA-GEIGY → NOVARTIS) that has been very abundantly used worldwide in agriculture, hygiene and veterinary insecticides. In sheep, diazinon was particularly appreciated for the control and prevention of sheep scab mites, blowfly strike and lice. It has a high affinity for wool lipids, where it dissolves after topical treatment and remains for a long period of time ensuring several weeks and even months protection against re-infestation. However, this also leads of high diazinon residues in the wool of treated sheep.

Usage of diazinon products in sheep strongly declined after several countries imposed very strict safety precautions and prohibitive dip wash disposal regulations (e.g. the UK & Australia) for all dips in the late 1990s. As a consequence, using these products became rather inconvenient and often also expensive. Soon after, NOVARTIS, the market leader for diazinon products for sheep, divested all its organophosphates for strategic reasons, including its diazinon sheep brands (NEOCIDOL, TOPCLIP). Nowadays, in many countries sprays and dips have been vastly replaced by ready-to-use pour-ons and injectables that have become affordable, are much more convenient than sprays and dips, and as effective. Diazinon is still abundantly used worldwide in insecticide-impregnated ear-tags for fly control on cattle.

All organophosphates are veteran pesticides developed in the 1950s-1960s and are basically contact insecticides. This means that when the parasite comes in contact with it (e.g. during the blood meal, after landing on a treated host, etc), the active ingredient that impregnates the host's hair coat penetrates through the cuticle (i.e. the "skin" of insects and other arthropods) into its organism and disturbs essential biological processes in the parasite's body, in this case its nervous system.

After administration to livestock or other animals, organophosphates do not have a systemic mode of action, i.e. they are not transmitted to the parasite through the blood or the host. Topically administered organophosphates are very poorly absorbed through the skin of the hosts, and what is absorbed is quickly broken down and/or excreted. Consequently the concentration reached in the blood is too low to kill blood-sucking parasites.


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.