Dewomers are chemicals (drugs) that have been evaluated and tested (effectiveness and safety) for use in animals to remove worm parasites. For the most part, pharmaceutical companies will not market a dewormer unless it is essentially 100% effective. As long as dewormers remain effective (at the manufacture’s recommended dosage), control is relatively easy and cost effective. However, resistance to almost all dewormers has been developed by many worm species. Therefore, reliance on the use of dewormers has become limited. Only FDA approved dewormers (see Classes below) can be used legally without restrictions. All other dewormers, if used, are “extra-label” and are subject to specific regulations as delineated by FDA. Because of public concern over food product residues and environmental contamination with chemicals that may be harmful, the FDA has recently revised the rules and regulations governing use of chemicals in food animal production. In summary, producers and veterinarians have to pay attention to “extra-label” use, which means using a product other than for which it is approved. Because goats are a relatively minor livestock species, pharmaceutical companies can not recover the costs that would be incurred for them to pursue approval and labeling. For a veterinarian to use a dewomer “extra-label”, there has to be a valid veterinarian-client relationship. The veterinarian has to have contact with the animals and make a diagnosis that the parasite situation is potentially life threatening. The veterinarian has to establish that none of the approved dewormers will work (i.e. fecal egg count reduction testing). Once the approved dewormers have been tested and if none work, then other dewormers can be used “extra-label.” Table 1 provides Food Animal Residue Avoidance Databank (FARAD) recommendations on the dosage and withdrawal times for commonly used dewormers. The veterinarian has to take responsibility for prescribing the dewormer and the producer has to take responsibility for using it properly. In the absence of a valid veterinarian-client relationship, the producer is restricted and can not legally use an unapproved product “extra-label.”

Classes

The three general classes of dewormers are benzimidazoles, imidazothiazoles and macrolides. The more commonly used benzimidazole dewormers are fenbendazole (Safeguard, Panacur) and albendazole (Valbazen); imidazothiazole dewormers are levamisole (Levisol, Tramisol) and morantel tartrate (Rumatel) and macrolide dewormers are ivermectin (Ivomec) and moxidectin (Cydectin). Of these, only fenbendazole and morantel tartrate are approved for use in goats. All others would be used as extra-label. A number of these dewormers have gone off patent and are now marketed under different generic names.

Formulations

Formulations of dewormers include drench, injection and pour-on. In addition, some dewormers are marketed in feed supplement blocks, mineral mixes, pellets and cubes. For goats, only the drench formulation of fenbendazole and the feed formulation of morantel tartrate are approved for use.

Administration

Oral administration is preferred and with drenches, it is very important to make sure the product is delivered over the base of the tongue. By doing so, the dose is delivered to the rumen where it will be mixed with the ingesta and then distributed evenly throughout the gastrointestinal tract. If the dose is delivered into the front part of the mouth, some may be spit out (wasted = reduced dose) and when swallowed the reflex may stimulate closure of the esophageal groove which allows what is swallowed to bypass the rumen. When the rumen is bypassed, the dose goes directly into the omasum (third stomach) and moves quickly through the gastrointestinal tract, thus not allowing sufficient time for the anthelmintic to achieve full effectiveness.

The other form of oral administration is in feed products which does not ensure that all animals will receive an effective dose because individual animals utilize these products differently. Some animals eat more/less than others due to their appetite, their place in the “pecking order” or they just may not like the formulation (specifically supplement blocks and mineral mixes).

If one elects to use injectable products (not recommended), injections are subcutaneous (under the skin) and best administered in an area of exposed skin (usually under the front legs) so that one can see the dose being delivered. It is best to not “tent” the skin, just lay the needle on the skin and insert quickly. If the skin is tented, the needle may come out the other side and the injected material will be administered on the skin surface (again wasted). If the injection is given in an area covered by hair, it can be difficult to ensure that the needle actually penetrates the skin and the dose is delivered appropriately. Sometimes the injected material will run back out of the needle hole (again wasted), so make sure to press a finger over the injection site for a few seconds to prevent leakage.

If one elects to use a pour-on product (not recommended), the material has to be delivered on to the skin. Parting of the hair (if long) may be necessary to achieve this. There are mixed reports as to whether pour-ons (approved for use in cattle only) work on goats. For the most part, pour-ons do not seem to be that effective in goats.

Table 1. Commonly used dewomers in goats (Oral route of administration only)

Resistance

Make sure that the exhibition center provides adequate housing, that pens are cleaned and disinfected and that ventilation is adequate. Make sure that all animals entering the show will be examined by the show veterinarian and that all state and local animal health laws will be enforced. Work with your veterinarian to establish a herd health program for your show goats and for the goats staying home that will be exposed to the show goat on its return. Do not mask signs of illness in your goat. If it is sick then stay home. Make sure that you have a Scrapie Tag for your goat (wethers excluded) and that you have any required health tests performed and that you have a current Certificate of Veterinary Inspection. Minimize stress on your goat by providing it with a pen that is as close to those in the exhibition facility as is possible and use the same bedding, feed and water source as you will have at the show. Keep fans on the goat at home, the white noise they produce will be the same as you will recreate at the show. Transport your goat in your own trailer. Avoid traveling in a commercial trailer or commingling with other livestock.

The major problem encountered in controlling nematode parasitism in goats is the resistance that many worm populations (specifically H. contortus) have developed to essentially all of our dewormers. Resistance has developed primarily because dewormers have been used and rotated too frequently and many times under-dosing occurs. Continuing to use such a dewormer will increase the selection of more resistant worms which will eventually result in a population of “superworms” that can’t be controlled with drugs. There is no “silver” bullet that can be relied on. Resistance is genetically controlled and once it is established, it is set in the population and those dewormers can no longer be used effectively.

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