Brand: TRI-ZAP ® Insecticide Catle Ear-Tag

Company: Y-TEX

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


CHEMICAL CLASS of the active ingredient(s):

INDICATIONS: CATTLE (beef & lactating dairy cows)

PARASITES CONTROLLED (spectrum of activity)


  • Controls Horn Flies for up to four months with two tags per head.
  • One or two tags per head controls Face Flies for up to two months.
  • Two tags per head controls Lice and Spinose Ear Ticks for up to
    three months.
  • All animals in the herd should be tagged.
  • Remove tags in fall.


  • LD50 (acute oral) in rats: 204 mg/kg (for the tag, according to MSDS)
  • LD50 (acute dermal) in rats: >5000 mg/kg (for the tag, according to MSDS)

Suspected poisoning? Read the articles on abamectin safety and 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

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


Risk of resistance? So far there are no report on resistance of horn flies to abamectin or other macrocyclic lactones. But it must be assumed that prolonged uninterrupted exposure to macrocyclic lactones would sooner or later lead to resistance development. Resistance of horn flies (Haematobia irritans irritans) to synthetic pyrethroids is widespread worldwide, and can be very high, regardless of the delivery form (ear-tag, pour-on, spraying, dust bags, etc.). There are also reports on horn fly resistance to organophosphates, but it is less frequent ands stronger than to synthetic pyrethroids.

The synergist in the formulation (PBO) is supposed to neutralize resistance of parasites to pesticides due to so-called metabolic resistance (enhanced detoxification) caused by mixed function oxidases (= MFO), which is one among several mechanisms by which parasites can become resistant to pesticides of many chemical classes. PBO specifically inhibits the activity of MFOs. If metabolic resistance is caused by other enzymes than MFOs, or if resistance is (also) due to other mechanisms such as target site insensitivity, reduced penetration or behavioral modifications, it won't be neutralized by PBO. In the vast majority of cases producers affected by resistant parasites do not know which mechanisms make the parasites resistant, and it is mostly not possible to find it out. Consequently, whether the synergist PBO helps to overcome resistance or not is in fact a lottery.

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 effective against all the concerned parasites.

A very reasonable strategy to prevent or at least delay resistance development is to rotate each year between chemical classes. For preventing or at least delaying horn fly resistance best is to rotate each year between organophosphates, synthetic pyrethroids and macrocyclic lactones. Macrocyclic lactones are available also as pour-ons for the control of horn flies. Injectables and drenches do not control flies or other external 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: USA
GENERIC BRANDS available? Not yet in most countries. So far there are no comparable ear-tags combining a macrocyclic lactone with a synthetic pyrethroid.

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

For an overview and a list of the most used insecticide-impregnated ear-tags click here.


TRI-ZAP Insecticide Ear-tag for Cattle is one of the few insecticide-impregnated ear-tags containing a macrocyclic lactone, and the first only combining a macrocycliclactone with a synthetic pyrethroid.

Abamectin, one of the first macrocyclic lactones developed, was introduced already in the 1980s (by MSD AGVET). As all macrocyclic lactones, abamectin is an endectocide, i.e. it is simultaneously effective against external parasites and against internal parasites (mainly roundworms). Administered as an ear-tag it is not approved for the control of inernal parasites, probably because the concentration achieved in the blood is insufficient for this purpose. Abamectin is considered as the "cheap" ivermectin, with a similar spectrum of efficacy but less potent and slightly more toxic. Abamectin is vastly used in agricultural and hygiene pesticides worldwide, including the USA. Interestingly it is also abundantly used in livestock and pets in Australia and New Zealand, but very scarcely in Europe and the USA.

All macrocyclic lactones are both contact and systemic parasiticides. When parasites land on a treated host 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. The systemic mode of action means that macrocyclic lactones also work against parasites through the blood of the host, and this regardless of whether they are administered by injection, orally (drench), or topically (pour-ons). After topical administration (pour-on, ear-tag), part of the administered active ingredient that impregnates the hair coat is ingested through licking and grooming, and after ingestion it gets into the host's blood. Part of the active ingredient is also absorbed transdermally, i.e. through the skin and also gets into the host's blood. And part remains in the hair-coat. This is certainly so also in this particular abamectin ear-tag. But the amounts that finally reach the host's blood are probably insufficient for controlling internal parasites.

Zeta-cypermethrin is one of several standard isomer mixtures of cypermethrin (see below). Cypermethrin is one of several Type-II synthetic pyrethroids introduced by ICI & SHELL in the 1970s. It is a broad-spectrum insecticide effectiv against numerous insect and tick species. Worldwide it is massively used in veterinary products as well as in agricultural and hygiene pesticides.

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. Consequently 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.

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 or 80:20 cis:trans ratio. Zeta-cypermethrin is a mixture of 8 isomers with a 48:53 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. 

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, 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 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.

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. Face flies remain shorter on the hosts and protection may not last as long as that of horn flies. Efficacy against ticks depends strongly on the behavior and characteristics of each tick species. Ear ticks are obviously exposed to high doses of the active ingredient release by the ear-tags around the ears. But many ticks attach to cattle in body parts (e.g. the underbelly, the udders, the perineum, below the tail, etc.) that are poorly reached by the active ingredient released by the ear-tags and may not be sufficiently controlled.


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. 

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