HOW-TO SESSION: LIFE STAGE MANAGEMENT


full resistance. When monitoring the ERP it is only necessary to collect fecals from a subset of the resi- dent population (often the horses classified as higher egg shedders). As an example, if ivermectin was last used, the expected ERP is 6–8 weeks. Collect- ing fecals from a group of young horses 4 weeks after ivermectin treatment will help determine whether the drug is still suppressing strongyle egg counts as long as expected.


4. Discussion


Despite the increasing prevalence of drug resistant P. equorum populations on breeding farms world- wide, deworming programs for young horses have undergone minimal changes during the past sev- eral decades. Contemporary surveys of stud farm managers suggest that some of the reluctance to modify traditional, often intensive, interval-based deworming protocols is due to their uncertainty that adopting a more comprehensive, surveillance-based approach to parasite control with a focus on P. equo- rum will result in tangible, measureable benefits for the farm. Conditions are ideal for veterinarians to market their knowledge as well as diagnostic fecal assays. Continue to enlighten stud farm managers and foal owners about the health risks associated with clinical and even subclinical P. equorum infec- tions. Without proper diagnostics, including FEC, upper respiratory tract disease secondary to ascarid larval migration could easily be mistaken by lay personnel for viral or bacterial infections. Foals experiencing chronic, ascarid-induced pulmonary inflammation might be more susceptible to other opportunistic respiratory pathogens. Suboptimal growth and poor body condition among weanlings may not be nutritional in origin but the results of P. equorum infection. The well-known threat of as- carid-induced impaction colic affects not only wean- lings, but has been reported in yearlings and young adults as well. These potential health risks may help convince foal owners and breeding farm man- agers to invest in an FEC surveillance program to ensure their deworming program is effectively con- trolling indigenous P. equorum populations. Before making any deworming recommendations, consider providing a physical examination of indi- vidual farms using a simple questionnaire to cap- ture information about management practices, herd demographics, and deworming history. Assess the farm in terms of stocking density, size, and overall condition of pastures/paddocks and labor available to help decide which nonchemical parasite control strategies are realistic and feasible for that particu- lar operation. Obtain a detailed history about an- thelmintic use spanning at least the past 3–5 years with a focus on when foals receive their first de- wormer, the frequency of treatments, and which drug classes are routinely administered during the first year of life. Summarize results of any fecals that have been performed. Document if there have


476 2016  Vol. 62  AAEP PROCEEDINGS


been any suspected or confirmed cases of parasite- related disease in foals, weanlings, or yearlings. Using information obtained during the farm visit, customize a parasite control plan that begins with strategies to reduce environmental parasite egg and larvae burdens. These husbandry options include cross-grazing pastures with other ruminant species, keeping pastures mowed to remove roughs, harvest- ing a hay crop at the end of the grazing season, and resting pastures for at least several months during periods of warm ambient temperatures sustained above 85°F to optimize dessication of vulnerable strongyle larvae. If pastures are harrowed, remind owners that this procedure should only be performed during hot, dry periods and pastures rested for 3–4 weeks or longer before reintroducing mares and foals. Bi-weekly manure removal from favorite loafing areas for mares and foals such as around run-in sheds or near gates and waterers remains one of the most effective methods to reduce exposure to infective larval stages. Although fresh manure should never be spread on active pastures, properly composted manure can attain high-enough temper- atures to kill both strongyle larvae and ascarid eggs.46 If possible, foals and weanlings should be turned out onto the farm’s cleanest pastures. Before a deworming protocol can be designed it is necessary to determine which drug classes are effec- tive against ascarids and cyathostomins on that par- ticular farm. Prior to weaning, focus on control of P. equorum. In the older weanling control of small and large strongyles and tapeworms must be consid- ered. Begin with an easy-to-implement FEC sur- veillance program that is economical and labor friendly in terms of sample collection. Agree on basic guidelines for the program. One common goal is to protect the health of the individual foal or weanling while simultaneously minimizing egg shedding using the fewest number of drug treat- ments possible. Unless medically indicated, delay the first anthelmintic treatment for foals until they are 2–3 months of age. Reasons to consider ther- apy at a younger age include treatment of confirmed, clinically symptomatic S. westeri infections or clini- cal suspicion that foals are harboring dangerously high burdens of migrating ascarid larvae. On farms accustomed to deworming foals younger than 8 weeks of age, consider screening a group of 2–6 week-old foals to demonstrate the lack of any signif- icant fecal egg shedding prior to 8–10 weeks of age. These results reinforce the time required for ascarid and cyathostomin infections to achieve patency and may help farm managers feel more comfortable about pushing back the age for first drug treatments without worrying about foals contaminating pas- tures with high egg counts. If fear of S. westeri is a reason for early drug treatments, re-examine the deworming strategies for the periparturient mare to deflect unnecessary drug treatments away from young foals. Ivermectin administered the month before foaling or within the first couple of days post-


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