Brand: AGRESSOR ® Insecticide Ear-Tag

Company: Y-TEX

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


  • abamectin: 8%
  • piperonyl butoxide: 18%
  • Tag weight: 9 g

CHEMICAL CLASS of the active ingredient(s):

INDICATIONS: CATTLE (beef & lactating dairy cows)

PARASITES CONTROLLED (spectrum of activity)


  • Two tags per animal, one in each ear.
  • Tags remain effective for up to 12 weeks.
  • All animals in the herd should be tagged.
  • Remove tags as recommended by the manufacturer.


  • LD50 (acute oral) in rats: 225.4 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 article on abamectin safety in this site.

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

  • Meat: NIL (ESI 42 days)
  • 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 & buffalo flies (Haematobia 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 & buffalo flyresistance 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.

For this particular tag, considering that resistance to abamectin is not yet problem in horn & buffalo flies or any other external parasite of cattle, it is unclear how the PBO in the tag can contribute to product efficacy. PBO has no own efficacy against susceptible or resistant buffalo flies, and it does not significantly enhance the efficacy of abamectin against susceptible flies either.

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

A very reasonable strategy to prevent or at least delay resistance development is to rotate each year between chemical classes. Best for preventing or at least delaying buffalo fly resistance is to rotate each year between organophosphates, synthetic pyrethroids and macrocyclic lactones. Macrocyclic lactones are available also as pour-ons for the control of buffalo 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: Australia
GENERIC BRANDS available? Not yet. So far there are no comparable ear-tags with abamectin or other macrocyclic lactones.

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.


XP 820 Insecticide Ear-tag for Cattle is one of the few insecticide-impregnated ear-tags containing a macrocyclic lactone.

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). As for other macrocyclic lactones, abamectin has no efficacy whatsoever against tapeworms and flukes. It 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, also in Australia. Interestingly, abamectin it is only marginally used in veterinary products in the USA and Europe.

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.

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) buffalo 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. Efficacy against other insects and ticks is insufficient because they bite or attach to the host 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.


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.