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A NEW PRACTICAL SERVICE TO ASSIST IN THE
MANAGEMENT OF SHEEP & GOAT PARASITES
By: A. David Scarfe
Usefulness of Quantitative Assessment
Producers have attempted to manage parasite problems in several different ways. Typical approaches have included regular short term (every 3-4 weeks) deworming, strategic deworming at assumed critical times of the year and when clinical signs of disease are seen (anemia, bottle-jaw, or death). All of these approaches are second guessing the real extent of the parasite problems. Some producers seek help from their local veterinarian who does a fecal egg flotation. These fecal examinations give one an idea of what parasite eggs are present but do not adequately quantify the extent of the parasitism. It is important to know how heavily parasitized the animals are because goats are quite able to carry some parasites without clinical or subclinical (seen or unseen) damage. It is best to intervene before numbers get high enough to cause damage. It is also important to know the level of infection of different parasite species, as each of the most damaging parasites (the barberpole worm, coccidia, flukes and tapeworms) are controlled with different drugs.
Several other factors complicate parasite management. For example, transmission rates vary from year to year as well as during different times of the year. They also vary in response to general management practices, climate and a multitude of other conditions. In general, we have found that there is no one single approach that is appropriate for all conditions and all parts of the country. The way we manage parasites and use drugs in Texas will not always work in Oregon or Maine or Florida. Unfortunately, most times we are guessing at the parasite problems in a herd; it is usually far better to assess a problem fully and then plan management strategies around known situations.
Often the approaches we have taken in managing parasites may do more harm than good. It needs to be emphasized that if we wait until clinical signs develop, serious damage has already been done to the animal, and it may take several months for the animal to fully recover, even if it is treated immediately and the signs rapidly disappear. A single animal in a herd showing clinical signs usually indicates a problem in the whole herd. Rapid, repeated treatments (e.g. every 3-4 weeks) of animals may solve immediate problems in a herd, but it is probably the most ideal way to select parasites that are resistant to the drugs presently available. Without doubt, far more is gained by a producer if he knows to what extent his animals are parasitized and also which parasites are causing real or potential problems. Quantitative parasite monitoring can remove much of the guess work from management and help producers determine potential problems, when to adjust management practices, the most appropriate drugs to use and the time to use them.
This monitoring program grew out of University research in which the numbers of eggs per gram (EPG) of feces were counted for each parasite species present, in order to quantitatively assess the degree of specific parasitism in experimental herds. The method is also used by pharmaceutical companies to field test the efficacy of different drugs prior to Federal approval. For a drug to be approved by the Food and Drug Administration (FDA) it has to initially be shown to be effective, and this requires a quantitative assessment. About three years ago, we began to test the feasibility of using EPGs in commercial herds. The demand grew to the point where Veterinary Schools and State Veterinary Diagnostic laboratory personnel were unable to accommodate the demand. While the technique is relatively simple, it is more time consuming than a simple flotation. This is partly the reason why most veterinary clinics do not offer the service. OVA-CAP has addressed these issues and has set up an efficient, convenient and low cost service to assist the industry.
The convenience of the program is based on mailing a sampling kit to those requesting the service. The kit has containers for fecal samples, a submission form, a return address label and postage. A producer or veterinarian obtains fecal samples from a minimum of five individual goats in a herd and places the feces from each animal in a separate container. The submission form needs to be completed and the form and samples placed in the kit which is then dropped in the nearest mailbox after affixing the return label and the stamps. The laboratory usually receives the kit in one to two days, does the counts and mails a report to the producer and to the referring veterinarian.
In all cases, submission requires that a referring veterinarian (usually a client's local vet) be the contact person. Usually, if a client requests the service, there is no charge from the veterinarian, but the veterinarian can be a ready source for further help and information and a source of appropriate drugs. This is particularly important as most drugs are not approved by FDA for use in goats; legally, these drugs can only be used under prescription, or the recommendation, of a licensed veterinarian. In addition, because different drugs are effective against different parasites that cause the primary damage to sheep and goats, the veterinarian can help determine the best drug to use. The referring vet can also provide information on withdrawal times required for each drug. This is particularly important if goats producing milk or meat for human consumption are treated.
The report supplied by OVA-CAP contains the names and addresses of the client and veterinarian, a description of the herd, when they were last dewormed, the drugs and dosages used, and the eggs per gram counts for all the parasites observed. The report lists the severity of each parasite species in the herd and a series of recommendations. The recommendations are based on the information supplied, the location of the herd, the time of the year and the numbers of each parasite found. Importantly, the recommendations are for the whole herd as the overall picture is most significant. In most cases parasite management should be done on a herd basis rather than an individual basis because herd health management is a far more cost efficient and practical approach to preventative medicine.
Both OVA-CAP Laboratories offer three services: a spot check; regular routine monitoring; and a drug efficacy test.
Drug Efficacy Determination
There is considerable hearsay about different anthelminthics being ineffective, or that parasites are resistant to specific drugs. Very few studies have documented resistance. A few reliable scientific articles have shown that the barberpole worm (Haemonchus contortus) has significant resistance to thiabendazole (TBZ) and occasionally resistance to other drugs in a few localities through the country (TBZ is the only currently available anthelminthic approved for goats!!). Unfortunately there are many unsubstantiated reports of resistance which may have resulted from improper use of a drug, rather than real resistance. As a result, several very effective drugs may not be used. The only way resistance can be verified is through quantitative assessment.
To determine efficacy of a deworming drug, two fecal samples are required from several individual animals in a herd: one immediately before, and one about 7-10 days after using a product. The same individual animals need to be sampled both times and the reduction in the number of eggs calculated. To be effective, a particular drug should reduce the EPGs by greater than 90-95%. Anything less than this suggests either drug resistance or an inappropriate dosage or the drug has been incorrectly administered. The best time to determine whether a drug is effective in reducing parasite loads is at the beginning of a season, usually spring, when parasite numbers are high but not excessive. After determining that a chosen drug is effective, it is best to use it for the whole year unless specific circumstances dictate the use of a different drug.
The program that has been set up by OVA-CAP to assist the industry can provide an efficient and convenient service. For once, a service is available to provide real answers to real or imaginary parasite questions. While it is not a replacement for all other parasite management tools, it provides an economical way to quantitatively assess parasitism. OVA-CAP laboratories are offering the service to producers and veterinarians at $35 per herd evaluation (five samples). They provide the full kit, including postage. Reports are sent to the client and veterinarian at no extra cost. This compares favorable with the standard fecal (flotation) exam that costs between $3 and $6 per sample.
Interested readers should contact either of the OVA-CAP Parasite Monitoring Laboratories directly for additional information or availability of the parasite monitoring kits.
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