Brand: FLECTRON ® Insecticide Ear-Tag

Company: ZOETIS

DELIVERY FORM: «ear-tag» to be applied to the front or back of the ear.


  • cypermethrin: 8.5% (0.935 g/tag) (50:50 cis:trans ratio)
  • Tag weight: 11 g

CHEMICAL CLASS of the active ingredient(s): synthetic pyrethroid

INDICATIONS: CATTLE (beef & dairy)

PARASITES CONTROLLED* (spectrum of activity)

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


  • One tag per animal is usually sufficient to achieve acceptable levels of fly control.
  • Two tags may be necessary, one on each ear, where head fly and face fly attack is very severe.
  • Flectron ear tags provide protection throughout the fly season.
  • For maximum benefit tags should be applied at the beginning of the season before fly populations build up.
  • For complete control the entire herd should be tagged.
  • Remove tags after the fly season.


  • LD50 (acute oral) in rats: 250-4123 mg/kg (for the a.i., according to MSDS)
  • LD50 (acute dermal) in rats: 1600 mg/kg (for the a.i., according to MSDS)

Suspected poisoning? Read the article on cypermethrin safety in this site.

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

  • Meat:  NIL.
  • Milk for human consumption: NIL.

2nd-generation synthetic pyrethroids (e.g. cyfluthrin, cyhalothrin, cypermethrin, deltamethrin, permethrin, etc.) are irritant to the eyes and the skin, both of humans and livestock. However, delivery through insecticidal ear-tags is usually less irritant than through pour-ons.

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 horn flies (Haematobia irritans) to synthetic pyrethroids (incl. cypermethrin) is widespread worldwide, and can be very high, regardless of the delivery form (ear-tag, pour-on, spraying, etc.). Cases of resistance to synthetic pyrethroids have also been reported for stable flies, lesser houseflies & black flies, but strength & prevalence is usually low.

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

Alternative chemical classes/active ingredients to prevent resistance of external parasites through product rotation:

These alternative products may not be available in all countries, or may not be available as ear-tags, or may not be effective against all the concerned parasites.

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: UK, Ireland + other EU countries
GENERIC BRANDS available? Yes, perhaps not with cypermethrin, but with comparable synthetic pyrethroids.

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

For an overview on the most used insecticidal EAR TAG brands click here.


FLECTRON Insecticide Ear-tag for Cattle from ZOETIS is one of the numerous insecticide-impregnated ear-tags for the control of flies on cattle wordlwide, although rather few are approved in the EU. 

Cypermethrin is one of several veteran type-II synthetic pyrethroids. It was introduced by ICI & SHELL in the 1970s. Worldwide it is massively used in veterinary products as well as in agricultural and hygiene pesticides.

Insecticide-impregnated ear-tags are designed to slowly release the insecticide into the animals hair-coat to ensure protection for months. Whether most of the insecticide is released at the beginning and only a little at the end, or release is homogeneous depends on the composition of the matrix and the behavior of the active ingredient(s) in it. However, after 2 to 3 months the amount released progressively decreases to drop below the amount that is required to ensure full fly control. This means that at a certain point flies and other parasites may be exposed to sub-lethal doses, which is generally considered as a factor that favors resistance development. For this reason the tags should be removed after 3-4 months following the manufacturer's use recommendations, and either replaced by new ones or the animals should be left untagged.

Once the active ingredient is released, efficacy strongly depends on the spreading of the active ingredient(s) along the animal's hair coat to other parts of the body. This depends on factors such as solubility of the active ingredient in the hair and skin lipids. Persistence in the hair-coat depends on other features of the active ingredient(s) such as volatility, resistance to sunlight, solubility in water, etc. As a general rule, some body parts will get less active ingredient than other parts and protection there will be lower, e.g. the legs, the underbelly, the udders, below the tail, etc.  Animal behavior (licking, grooming, rubbing, etc.) plays a role as well. It has been shown, that if only half of the animals in a herd are tagged, those untagged will also be protected against flies to some extent, indicating that part of the active ingredient is transferred from tagged to untagged animals. However, this also means that tagged animals will lose part of the active ingredient and protection will be shorter and/or control will be poorer.  For this reason all animals in a herd should be tagged because this reduces the impact of animal behavior in efficacy and length of protection. However, since individual animal behavior plays a role in efficacy and length of protection, it must be accepted that protection will not always be the same in all the animals in a herd.

All synthetic pyrethroids are veteran pesticides developed in the 1970s-1980s 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 of the parasite (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, synthetic pyrethroids 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 synthetic pyrethroids are very poorly absorbed through the skin of the hosts, and what is absorbed is quickly broken down and/or excreted. For this reason the concentration reached in the blood is too low to kill blood-sucking parasites. But this is why they are considered rather safe to mammals, both humans and livestock (cats are an exception: pyrethroids are toxic to them!) and why they leave rather low residues in meat and milk.

Control of susceptible (i.e. non-resistant) horn flies is usually excellent, because they spend a lot of time on cattle and thus are exposed to the insecticide for a long period of time. But as already mentioned, horn flies have developed high resistance to all synthetic pyrethroids in many countries. In contrast with the behavior of horn flies, stable flies bite the treated animals anywhere in their bodies (often in the legs) and remain attached and thus exposed to the insecticide only during their blood meals that last a few seconds or minutes, which is often too short to kill them. More or less the same applies to most other nuisance and biting flies (e.g. face flies, head flies, horse flies, black flies, lesser houseflies, etc.): they remain only shortly on the animals, which is often insufficient to kill them and control will be only partial.

All synthetic pyrethroids have a certain repellent effect, mainly on mosquitoes. The repellent effect on flies is mostly weaker than on mosquitoes.

It is useful to know that the active ingredients of many synthetic pyrethroids consist in a mixture of various optical isomers, typically those called "cis", and those called "trans". Cypermethrin has 8 isomers, 4 cis and 4 trans. Manufacturers of active ingredients usually supply the raw material in standard qualities, for cypermethrin typically e.g. in a 40:60, 50:50 or 80:20 cis:trans ratio. It happens that the efficacy against parasites and the mammalian toxicity of these isomers are significantly different. Typically cis isomers are more effective insecticides but also more toxic to mammals. Obviously a cis/trans 80:20 mixture is more potent than a cis/trans 40:60 mixture. Qualities with higher cis content are usually also more expensive. And the higher the percentage of the most active isomer, the lower the rate that is required for achieving the same efficacy. 


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.