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Title: Parasite control on thoroughbred studs
Author: Hallowell-Evans, Cara Louise
ISNI:       0000 0004 7428 5440
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2017
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Gastrointestinal parasite infections impact on the health and welfare of Thoroughbreds (TB). The parasites of concern include the strongyles; cyathostomins and Strongylus vulgaris, Parascaris equorum and Anoplocephala perfoliata. In addition, there is increasing recognition of liver fluke infections in horses. Life-long parasite control is needed and use of anthelmintic drugs is the major approach, but decades of intensive anthelmintic usage has promoted widespread resistance particularly in cyathostomins and Parascaris equorum. Intensive anthelmintic usage is defined as the administration of an anthelmintic drug at set intervals, based on the original egg reappearance period (ERP) of the pioneer product, with the aim of egg output suppression; following the recognition and widespread nature of anthelmintic resistance targeted selective treatment regimens are now being advocated. Targeted selective treatment is defined by the American Association of Equine Practitioners (AAEP) as basing treatments during high transmission periods on diagnostic testing and identification of high egg shedding individuals in order to reduce pasture contamination while leaving a parasitic population in refugia, due to the current limitations in detection whole herd moxidectin and praziquantel treatments are still advocated annually as a minimum, with frequency dependent on a risk analysis and utilisation of available assays. The aim of this project was to identify parasite control practices on UK TB studs, determine drug efficacy on a subset of TB studs and evaluate the diagnostic potential of faecal diagnostic tests. Faecal diagnostic tests for F. hepatica and A. perfoliata were examined. A McMaster-based short method for F. hepatica was applied to known positive donkey (n=18) and horse (n=1) samples which were simultaneously evaluated with the standard sedimentation method. Mean egg per gram (epg) count was 21.0epg (0.2-138epg) and 31.0epg (0.4-202epg) for the short method and standard sedimentation, respectively. The centrifugal flotation (CF) method was investigated for detection of A. perfoliata eggs and compared to the validated double sugar flotation (DCF) test. In total 140 samples were tested. Of these, 25.7% (±7.2%, n=36/140) tested positive using CF and 22.1% (±6.9%, n=31/140) using DCF. Nine TB studs have undergone drug efficacy testing based on their anthelmintic use, control strategies and clinical disease concerns, mebendazole was tested on one stud, pyrantel on five studs; ivermectin on three and moxidectin on two. Tests were conducted for adults and youngstock independantly. The CF faecal egg count (FEC), sensitive to 1epg, was used to detect strongyle-type, Parascaris spp and A. perfoliata eggs. On studs where >10 animals showed > 50epg (strongyle), faecal egg count reduction tests (FECRT) were performed to determine resistance status. ERP was defined as when group arithmetic mean FEC post-treatment exceeded 10% of group FEC arithmetic mean pre-treatment. Larval culture and morphological identification of strongyle third-stage larvae were also performed. On stud B, youngstock [YS] (n=7) PYR efficacy was 98.5% (97.9-99.0%), ERP = 3 weeks, and 93.2% (91.9-94.3%) in mares (n=8), ERP = 4 weeks; stud D only YS (n=31) showed resistance to PYR (reduction = 58.8% (57.6-60.0%)), sensitivity to IVM (100.0% (99.9-100.0%)) but borderline efficacy to MOX (94.5% (93.9-95.1%); ERP 4 weeks); stud F showed PYR resistance (n=23 YS, n=13 mares) with 0.1% (0.0-0.7%) and 69.5% (67.0-71.8%) reductions, IVM and MOX efficacy were 100.0% (99.9-100.0%) but ERP shortened to 6 weeks (IVM) and 8 weeks (MOX) in YS; stud G YS showed PYR resistance (n=18, 67.5% (64.9-69.9%) reduction). One stud (stud E) was referred to the project due to high levels of tapeworm-related disease in broodmares (~60-70% of mares affected per year). All stock were tested using the CF and DCF faecal methods and University of Liverpool (UofL) serum ELISA (adults, n=86; YS, n=64). For adult stock 74.4% (±9.7%, n=58/78) recorded negative A. perfoliata FEC using the CF method and 79.5% (±9.0%, n=62/78) using the DCF; for YS (n=48) 75.4% (±10.8%, n=46/61) were recorded as negative by both CF and DCF. Over the study period February 2015 to Jul 2016 94.7% (±3.6%, n=142/150) of all samples tested by ELISA were reported to have a moderate to high infection intensity. Highest proportion showing high infection intensity (O.D. > 0.201) on ELISA occurred in June 2015 (100% of adults and YS). Despite intensive three monthly praziquantel treatments from February to September 2015, no apparent decline in O.D. values was noted for either cohort, but FEC analysis revealed fewer horses were FEC positive over time. A questionnaire survey was conducted with, questionnaires distributed to active studs (n=184) with the option to complete by post, online or telephone. Response rate was 39 studs (21.2%). FEC had been performed by 80.6% (±12.9%, n=28/36) but 17.1% (±12.2%, n=6/36) only used FEC at suspicion of disease. 97.1% (±5.7%, n=33/34) were very concerned about resistance to worming drugs, despite this 40.0% (±16.2%, n=14/35) of studs use intensive regimens with only 27.3% (±14.6%, n=10/36) having performed a FECRT. Faeces were only removed from pasture on 53.9% (±15.9%, n=20/38) of studs with harrowing being performed annually on 23 (59.0% ±15.4%, n=23/39) 60.0% (±16.2%, n=21/35) of studs use targeted selective management, however, not all of these studs correctly defined the principle of targeted selective treatment so true level of implementation is unknown. This work has provided vital information to TB studs about drug efficacy. By evaluating current diagnostic tests for their ability to detect infection with other parasites it raises the possibility of a holistic and time-efficient approach to targeted selective parasite control. It has highlighted the crucial role diagnostics have in detecting parasitic infection and parasite-associated disease and has identified current practice on stud. Together these findings can be used to better support targeted selective treatment of parasites in TB horses and improve parasite control on studs.
Supervisor: Hodgkinson, Jane ; Matthews, Jacqui ; Archer, Debbie Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral