HOW-TO SESSION: LIFE STAGE MANAGEMENT


partum remains a popular drug choice. Oxibenda- zole administered at a dose of 15 mg/kg is a reasonable treatment for foals with clinically signif- icant and symptomatic S. westeri infections. To determine which of the three major drug classes, (e.g., benzimidazoles, tetrahydropyrimi- dines, and MLs) are still effective against P. equo- rum, perform a FECRT on samples from foals with patent ascarid infections (e.g., positive FECs). To maximize efficient use of labor, the timing of these fecal collections can coincide with a farm visit to screen foals for Rhodococcus equi pneumonia or to administer vaccines or check mares for pregnancy. The fecal assay used should be reasonably priced and sensitive. Consider training a technician to perform the FEC in house to reduce overhead and cost to the client while generating a modest profit. When performing FECR calculations to evaluate drug efficacy, the author prefers the modified Wis- consin method due to its low egg detection limit. This method also increases the likelihood of detect- ing cestode eggs. If ivermectin resistance is identified among indig-


enous P. equorum populations, then pyrantel pamo- ate and fenbendazole or oxibendazole are the remaining drug classes to consider. On some farms using the higher dosage (13.2 mg/kg) for pyrantel pamoate improved efficacy against resistant as- carids.4,53 Likewise, there are two different dos- ages to consider when administering fenbendazole to juvenile horses. A dose of 10 mg/kg is recom- mended for youngsters less than 18 months of age. If ascarid resistance is detected at this dose, a lar- vicidal dose (e.g., 10 mg/kg administered once daily for 5 d) should be considered based on the reports of efficacy against both larval and adult stages of P. equorum.47,48 It has been the author’s experience that the larvicidal dose of fenbendazole has been effective at reducing P. equorum egg shedding when the single 10-mg/kg dose has proven unsatisfactory. Hopefully adequate ascarid control can be achieved with two effective drug treatments administered prior to weaning. On farms with open herds, eval- uate quarantine procedures for newly arrived foals and leverage the use of a larvicidal treatment with fenbendazole coupled with a FEC to reduce the risk of introducing drug-resistant ascarids. Close to weaning time, consider evaluating FEC in a repre- sentative group of foals as a screening tool to see whether the pre-weaning drug treatments targeting P. equorum have been successful. Among older weanlings, collect fecals from a rep- resentative group just prior to the next planned drug treatment. Use the FEC results to identify foals with patent strongyle infections that can be used to test drug efficacy against that group of parasites. The same three drug classes should be tested using the FECRT. Although there are numerous reports of benzimidazole-resistant cyathostomins, do not as- sume resistance is present until it is confirmed on that particular farm. Recent surveillance trials us-


ing FECRT have shown that drug-resistance pat- terns can vary between facilities within the same state.4,58 In some instances older weanlings may be shedding both ascarid and strongyle eggs and a sin- gle drug class might not be sufficient to control both nematodes. In this situation consider adminis- tering two different drug classes simultaneously. This strategy has been used successfully on farms with confirmed multidrug-resistant parasite popula- tions.4 If tapeworm infection is a concern, then one treatment administered between 6 and 12 months of age should include an effective cestocide such as the higher dose of pyrantel pamoate or dewormer con- taining praziquantel. On larger breeding operations it might be possible


to evaluate the efficacy of all three drug classes within one breeding season, given that different groups of foals can be used to test different anthel- mintics. On smaller operations with fewer foals, it will probably require several foal seasons to test all the drug classes against both ascarid and strongyle populations. It is helpful to remember that not ev- ery foal needs to be tested every time. If drug- resistant parasites are detected it is likely to be a farm-wide problem rather than an individual ani- mal problem. Although this article has focused on the foal and weanling, it is naïve to forget that broodmares rep- resent an important and intimate source of parasite exposure for their foals through nematode eggs and larvae shed in their feces or through their milk. An effective deworming program for the broodmare band helps control overall pasture parasite burdens awaiting each new crop of foals.


5. Summary


Deworming protocols for young horses during their first year of life have three major goals: prevent and/or decrease the incidence of parasite-related dis- ease in individual animals, reduce environmental contamination with parasite eggs and larvae, and accomplish the first two goals using the minimal number of effective drug treatments. Administra- tion of ivermectin to the periparturient mare should eliminate the urge to treat neonatal foals due to a fear of S. westeri. Prior to weaning, P. equorum is the primary pathogen of concern and should be the focus of anthelmintic treatments in foals 6 months of age and younger. Ideally, foals should receive their first treatment just as ascarid infections achieve patency at approximately 2.5–3 months of age. Benzimidazoles and tetrahydropyrimidines are the two drug classes most likely to demonstrate efficacy against ascarids. Ivermectin should only be used if efficacy is confirmed using the FECRT. Each drug class should be evaluated periodically on a farm by farm basis to ensure lack of resistance. After wean- ing, control of small and large strongyles and tape- worms become a consideration in drug selection. Macrocyclic lactones are a reasonable option for strongyle control. Praziquantel or a double dose of


AAEP PROCEEDINGS  Vol. 62  2016 477


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