Brand: DOUBLE BARREL ® VP Insecticide Ear-Tag


DELIVERY FORM: «ear-tag» to be applied through ear between second and third rib, halfway between ear tip and head.


  • lambda-cyhalothrin: 6.8%
  • pirimiphos methyl: 14%
  • tag weight: 9.5 g

CHEMICAL CLASS of the active ingredient(s):

INDICATIONS: CATTLE (beef & non-lactating dairy)

PARASITES CONTROLLED* (spectrum of activity)

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


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

  • Two tags per animal (one in each ear).
  • All animals in the herd should be tagged.
  • Apply when flies first appear in spring. Replace as necessary.
  • Tags remain effective up to 5 months.
  • Remove tags in fall.


  • LD50 (acute oral) in rats:
    • 56 - 70 mg/kg for lambda-cyhalothrin (according to MSDS).
    • 2400 to 5976 mg/kg for pirimiphos methyl (according to MSDS).
  • LD50 (acute dermal) in rats:
    • 632 to 696 mg/kg for lambda-cyhalothrin (according to MSDS).
    • 2200 - 3500 mg/kg n.a. for pirimiphos methyl (according to MSDS).

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

  • Read the product label

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. lambda-cyhalothrin) is widespread worldwide, and can be very high, regardless of the delivery form (ear-tag, pour-on, spraying, dust bags, etc). Resistance to organophosphates has been reported in several countries. However, resistance to synthetic pyrethroids is much more abundant and stronger, and it has been shown that pyrethroid-resistant horn flies are particularly susceptible to diazinon.

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.

From the point of view of resistance prevention & management, products such as this one combining active ingredients of two different chemical classes (with different mechanisms of action) make sense when used against parasites that are still susceptible to both chemical classes. In this case it is assumed that simultaneous development of resistance to two different mechanisms of action is less likely to occur than to a single mechanism.

If the parasites are already resistant to one of the chemical classe in the combination, the main benefit of such combinations is short-term peace of mind for producers: if one compound fails, the other one will do the job. However if resistance to one chemical class has already developed, best practice (besides other Integrated Pest Management measures) is to change to another chemical class with a different mechanism of action and to stop using the chemical class to which parasites are already resistant. Otherwise the risk is significant that the parasites become multi-resistant, i.e. simultaneously resistant to both chemical classes. And this can happen within a few years.

As already mentioned, it has been shown that horn flies resistant to synthetic pyrethroids are particularly susceptible to diazinon. For this reason rotating each year between these two chemical classes is a reasonable strategy to prevent or at least delay resistance development. Even better is to add a macrocyclic lactone (abamectin, doramectin, eprinomectin, ivermectin, moxidectin, etc.) into the rotation scheme, because the mechanism of action of these compounds is different from those of organophosphates and synthetic pyrethroids. Most macrocyclic lactones are available as pour-ons for the control of horn flies, a few ones also as ear-tags. Macrocyclic lactones formulated as 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? Probably not in the combination synthetic pyrethroidorganophosphate.

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

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


DOUBLE BARREL VP Insecticide Ear-tag for Cattle from MERCK ANIMAL HEALTH is one of the numerous insecticide-impregnated ear-tags for the control of flies on cattle.

Lambda-cyhalothrin is one of several Type-II synthetic pyrethroids and was introduced by ICI in the 1980s. It is moderately used in veterinary products, significantly more in agricultural and hygiene pesticides.

Pirimiphos-methyl is a veteran organophosphate pesticide introduced in the 1960s. It has a broad-spectrum of efficacy against numerous insects. It has been poorly used in veterinary products but more in agricultural pesticides. However, as most organophosphates it has been vastly replaced by more modern pesticides in numerous countries in the last decades.

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.

All organophosphatesynthetic pyrethroid pesticides were developed in the 1950s-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 topical administration to livestock or other animals they 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 they 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.

Control of susceptible (i.e. non-resistant) horn flies is usually excellent, because they spend most of their time on cattle and thus are exposed to the insecticide for a long period of time. And they remain mainly in the back of the animals, where the concentration of the active ingredient released by the ear-tags is rather high. Face flies remain shorter on the hosts and protection may not last as long as that of horn flies.


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.