Brand: DOMINATOR ® Insecticide Ear-Tag
Company: MERCK ANIMAL HEALTH
ACTIVE INGREDIENT(S) & WEIGHT
- pirimihos-methyl: 20%
- tag weight: 9.5 g
INDICATIONS: CATTLE (beef & dairy)
PARASITES CONTROLLED* (spectrum of activity)
* 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: 2400-5976 mg/kg (for the a.i. according to MSDS)
- LD50 (acute dermal) in rabbits: 2200-3500 mg/kg (for the a.i. according to MSDS)
Withholding periods (=withdrawal times) in days for meat & milk (country-specific differences may apply: read the product label)
- Meat: USA NIL.
- Milk for human consumption: USA NIL.
You may be interested in the following articles in this site dealing with the general safety of veterinary products:
- Safety for humans
- Safety for domestic animals
- Safety for the environment
- Hazard classifications of pesticides
Risk of resistance? YES, resistance of horn flies (Haematobia irritans irritans) to organophosphates has been reported in several countries. However, resistance to synthetic pyrethroids is much more abundant and stronger.
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.
- Macrocyclic lactones (e.g. abamectin, doramectin, eprinomectin, ivermectin, moxidectin, etc.) only as pour-ons. Injectables and drenches are ineffective against most external parasites.
- Synthetic pyrethroids (e.g. cyfluthrin, cyhalothrin, cypermethrin, deltamethrin, permethrin, etc.). However, horn & buffalo flies have developed resistance to these compounds in many regions.
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.
It has been shown that horn flies resistant to synthetic pyrethroids are particularly susceptible to diazinon, another organophosphate, and it is assumed that this also happens to some extent with other organophosphates, although to our knowledge it has not be confirmed yet. In any case 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.
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? YES, perhaps not with pirimiphos-methyl, but with comparable organophosphates.
Click here to learn more about GENERIC vs. ORIGINAL drugs.
For an overview on the most used insecticidal EAR TAG brands click here.
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 Animal Health but more in Crop Protection. 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 organophosphate pesticides were 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 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, 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.
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 active ingredient released by the ear-tags is rather high. Biting lice are also exposed to topical insecticides for a long period of time because they never leave the host. In contrast with the behavior of horn flies, face flies visit cattle only for feeding and remain exposed to the insecticide during shorter periods of time, sometimes too short to kill them.
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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