Worm control practices used by Thoroughbred horse managers in Australia: A national survey.

This study assessed worm control practices used by Australian Thoroughbred farm managers with an online questionnaire survey. The questionnaire comprised 52 questions (close-ended: 44; open-ended: 8) about farm demography and general husbandry practices, farm managers' knowledge of gastrointestinal nematodes (GIN) and their importance, diagnosis, worm control strategies and anthelmintics, anthelmintic resistance (AR) and grazing management. Following the pilot survey, the link for the questionnaire survey was sent to all (n = 657) registered members of the Thoroughbred Breeders Australia on 12th April 2020. The response rate for the questionnaire was 18.5% (122 of 675). The farm managers reported a good understanding of GIN and their importance in different age groups of horses as most respondents (70% of 122) perceived worm-related illness to be more important in young (i.e., foals, weanlings and yearlings) than adult (> 3 years old) horses. Although most respondents (93%, 113 of 122) used anthelmintics prophylactically to control GIN, only 15% (18 of 122) observed worm-related illness in their horses. Just under 40% of respondents were performing faecal egg counts, with less than 20% using the results of faecal egg counts to guide deworming decisions. The interval-based deworming strategy was the most common method (≥55% of 122 respondents) to control GIN in all age groups of horses. Macrocyclic lactones were the first choice of anthelmintics for all age groups of horses. Although the majority of respondents (88%, 107 of 122) perceived resistance in GIN against commonly used anthelmintics as an important issue in managing worms in horses, only 29% assessed the efficacy of anthelmintics and 91% (111 of 122) were unaware of AR on their properties. Grazing management practices, such as manure removal, were more frequently performed on smaller paddocks (<0.20 ha: 58%) than on larger paddocks (>0.20 ha: 18%). Multiple correspondence analyses showed that the likelihood of suboptimal worm control practices on small farms (n = ≤50 horses) was greater than that of medium (n = 51-100) and large (n = >100) farms. This study provides insights into the demography of Thoroughbred farms in Australia, husbandry practices used by stud managers and their knowledge about worms, control options and AR concerns, thereby paving the way for taking any initiatives to address the problem of AR in GIN of Australian Thoroughbred horses.

Understanding temporal and spatial distribution of intestinal nematodes of horses using faecal egg counts and DNA metabarcoding.

This study reports the spatial and temporal distribution of ascarid and strongylid nematodes in Thoroughbred horses by age category across different climatic zones in Australia over an 18-month period. Faecal samples (n = 2046) from individual horses were analysed using the modified McMaster technique for faecal egg counts (FECs). Strongylids were identified using PCR-directed next-generation sequencing of the second internal transcribed spacer (ITS-2) of the nuclear ribosomal DNA. Yearlings had the highest prevalence (82%) of strongyle eggs followed by weanlings (79%), foals (58%), wet mares (49%) and dry mares (46%). For Parascaris spp., foals had the highest prevalence (35%) followed by weanlings (21%) and yearlings (10%). The highest mean FECs for Parascaris spp. were observed in foals (525 eggs per gram [EPG] of faeces) while those for strongyles were in yearlings (962 EPG). Among horses that were classified as adults at the time of sampling, 77% (860 of 1119) of mares were low (i.e., <250 EPG) strongyle egg-shedders. Mean strongyle FEC counts were highest in the Mediterranean (818 EPG) followed by summer (599 EPG), winter (442 EPG), and non-seasonal (413 EPG) rainfall zones. Twenty-six nematode species were detected, with Cylicostephanus longibursatus (26.5%), Cylicocyclus nassatus (23.7%) and Coronocyclus coronatus (20.5%) being the most frequently detected species. Their richness and relative abundance varied with horse age, season and climatic zone. In addition, Strongylus equinus and Triodontophorus spp. (T. brevicauda and T. serratus) were also detected. This comprehensive study elucidates spatial (climatic zone) and temporal (i.e., seasonal) trends in prevalence and burdens of intestinal nematodes in Australian horses using non-invasive conventional and molecular methods. The information presented in this study is crucial for developing integrated management strategies to control horse parasites in farmed horses.

A national survey of anthelmintic resistance in ascarid and strongylid nematodes in Australian Thoroughbred horses.

This study quantified the extent of anthelmintic resistance (AR) in ascarid and strongylid nematodes against commonly used anthelmintics in Australian Thoroughbred horses. Faecal egg count reduction tests (FECRTs, n = 86) and egg reappearance period (ERP) tests were conducted on 22 farms across Australia. Faecal egg counts (FECs) were determined using the modified McMaster technique, and percent faecal egg count reduction (%FECR) was calculated using the Bayesian hierarchical model and hybrid Frequentist/Bayesian analysis method. The results were interpreted using old (published in 1992) and new (2023) research guidelines of the World Association for the Advancement of Veterinary Parasitology (WAAVP). The species composition of strongylid nematodes was detected utilising a DNA-metabarcoding method using pre- and post-treatment samples. Resistance was observed in strongylid nematodes to commonly used single-active and combination anthelmintics, including ivermectin (IVM %FECR range: 82%-92%; 95% lower credible interval (LCI) range: 80%-90%), abamectin (ABM: 73%-92%; 65%-88%), moxidectin (MOX: 89%-91%; 84%-89%), oxfendazole (OFZ: 0%-56%; 0%-31%) and its combination with pyrantel (OFZ + PYR: 0%-82%; 0%-78%). Resistance in Parascaris spp. was observed to IVM (10%-43%; 0%-36%), ABM (0%; 0%) and MOX (0%; 0%). When the new thresholds recommended by the WAAVP were used, AR was detected in six additional FECRTs for strongylids and three more tests for Parascaris spp., introducing resistance to OFZ and OFZ + PYR in the latter. Shortened ERPs (4-6 weeks) of strongylids were observed in 31 FECRTs in which AR was not detected at 2 weeks post-treatment for all the anthelmintics tested. Among cyathostomins, Cylicocyclus nassatus, Cylicostephanus longibursatus and Coronocyclus coronatus were the most prevalent species at 2 weeks post-treatment, whereas the main species appearing at five weeks following treatments with macrocyclic lactones were Cylicocyclus nassatus, Cylicostephanus longibursatus and Cylicocyclus ashworthi. After treatment with OFZ + PYR, the latter three, plus Coronocyclus coronatus and Cyathostomum catinatum, were detected at 5 weeks post-treatment. Overall, the study highlights the prevalence of AR in both ascarids and strongylid nematodes against commonly used anthelmintic products to control worms in Australian horses. The results indicate that ML combination products provided acceptable efficacy at 2 weeks. However, ERP calculations suggest that products work less effectively than previously measured. It is suggested to regularly monitor the efficacy of the anthelmintics and consider changing the worm control practices to better manage worms and AR in Australian horses.

Assessment of worm control practices recommended by equine veterinarians in Australia.

This study aimed to assess Australian veterinarians' knowledge, perceptions and treatment strategies for worm control in horses with an online questionnaire. The questionnaire comprised 64 questions covering various aspects of: (i) veterinary practice; (ii) the veterinarian's knowledge of gastrointestinal nematodes (GINs) and the importance of parasites in different age groups of horses; (iii) the diagnosis and control of worms; (iv) anthelmintics and anthelmintic resistance (AR); (v) grazing management; and (vi) the means of communication and the discussion between veterinarians and their clients regarding worm control. Following a pilot survey, a link for the questionnaire survey was sent to all (n = 1,148) registered members of Equine Veterinarians Australia in April 2020. The response rate for the questionnaire was 10% (118 of 1,148). The findings of this study illustrate veterinarians' good understanding of aspects of equine parasites, including control. However, respondents mainly recommended frequent, interval-based prophylactic deworming in young horses, and only 40% (96 of 239) diagnosed GIN infections based on faecal egg count (FEC) results in all age groups of horses. Furthermore, only 27% (88 of 330) of the respondents made deworming decisions based on FECs. Most of the respondents recommended macrocyclic lactones (MLs) for all age groups of horses (71%, 481 of 677), and the most frequently used method to calculate the dose of anthelmintics was by estimating the weight of animals visually (53%, 63 of 118). Although the majority of respondents (97%, 115 of 118) perceived AR to be a critical issue in managing worms in horses, 58% (67 of 118) of them were unaware of the status of AR on their clients' properties. Forty-two percent (50 of 118) of the respondents perceived the presence of AR in worms, including pinworms (16%), strongylins (15%), species of Draschia and Habronema (6%), Strongyloides westeri (2%) and tapeworms (1%). Twenty-seven percent (32 of 118) of the respondents rarely discussed equine worm control practices with their clients. This study provides insights into the perception and worm control practices recommended by Australian veterinarians to manage equine parasites. The findings highlight the importance of continued education and awareness of AR, and the use of non-chemical methods as well as consideration of the legislation of prescription-only use of anthelmintics based on FECs to achieve sustainable control of GINs in Australian horses.

Prevalence and diversity of ascarid and strongylid nematodes in Australian Thoroughbred horses using next-generation sequencing and bioinformatic tools.

The study presents the results of a cross-sectional survey to describe the epidemiology of ascarid and strongylid nematodes in horses, the impact of diverse climatic conditions on parasite diversity and the levels of faecal egg shedding in different age groups of managed Thoroughbred horses. Individual faecal samples (n = 1377) collected from 62 Thoroughbred farms across four climatic zones in Australia were analysed using the modified McMaster technique for faecal egg counts (FECs) and strongylid nematodes were identified utilising PCR-directed next-generation sequencing (NGS) of the second internal transcribed spacer of the nuclear ribosomal DNA (ITS-2). Across all age groups, the prevalence of ascarid and strongylid nematodes was 12% (95% confidence interval 10-14%) and 72% (70-74%), respectively. Based on strongylid FECs, yearlings had the highest prevalence (89%) followed by weanlings (83%), foals (79%), wet mares (61%), dry mares (59%) and stallions (54%). However, for Parascaris spp., foals had the highest prevalence (46%) followed by weanlings (32%) and yearlings (13%). The highest mean FECs for Parascaris spp. were observed in foals (418 eggs per gram [EPG] of faeces) while those for strongylids were in yearlings (1002 EPG). Of the adult horses (mares and stallions), 67% (489 of 729) and 11% (77 of 729) were low (i.e., ≤250 EPG) and moderate (i.e., 251-500 EPG) strongylid egg-shedders, respectively. Strongylid egg shedding varied across climatic zones, with the highest mean FECs in the summer rainfall (723 EPG) followed by non-seasonal rainfall (629 EPG), winter rainfall (613 EPG), and Mediterranean (606 EPG) rainfall zones. Twenty-three nematode species were detected using NGS, with Cylicostephanus longibursatus (28%), Cylicocyclus nassatus (23%) and Coronocyclus coronatus (23%), being the most abundant species. Three species of Strongylus (i.e., S. vulgaris, S. equinus and S. edentatus) were also detected. The nemabiome composition, species richness and relative abundance varied within horse age and between climatic zones. These empirical findings provide a comprehensive understanding of the prevalence of parasites within horse populations and the multifaceted factors that influence their occurrence, thereby allowing for the formulation of tailored strategies aimed at parasite control in domestic horses.

Egg reappearance periods of anthelmintics against equine cyathostomins: The state of play revisited.

Cyathostomins are the most common and highly prevalent parasites of horses worldwide. Historically, the control of cyathostomins has mainly relied on the routine use of anthelmintic products. Increasing reports on anthelmintic resistance (AR) in cyathostomins are concerning. A potential method proposed for detecting emerging AR in cyathostomins has been estimating the egg reappearance period (ERP). This paper reviews the data available for the ERP of cyathostomins against the three major classes of anthelmintics, macrocyclic lactones, tetrahydropyrimidines, and benzimidazoles. Published peer-reviewed original research articles were obtained from three databases (PubMed, CAB Direct and Web of Science) and were evaluated for their inclusion in a systematic review. Subsets of articles were then subjected to a review of ERP data. A total of 54 (of 134) studies published between 1972 and 2022 met the criteria for inclusion in the systematic review. Until the beginning of 2022, there was no agreed definition of the ERP; eight definitions of ERP were identified in the literature, complicating the comparison between studies. Additionally, potential risk factors for the shortening of the ERP, including previous anthelmintic use and climate, were frequently not described. Reports of shortened ERP for moxidectin and ivermectin are frequent: 20 studies that used comparable ERP definitions reported shortened moxidectin and ivermectin ERPs of 35 and 28 days, respectively. It is unclear whether the ERPs of these anthelmintics reduced to such levels are due to the development of AR or some biological factors related to horses, cyathostomin species, and/or the environment. The ERPs for other anthelmintics, such as fenbendazole and pyrantel, were frequently not reported due to established resistance against these drugs. Future research in horses is required to understand the mechanism(s) behind the shortening of ERP for cyathostomins. Based on this systematic review, we propose recommendations for future ERP studies.

Molecular diagnostics for gastrointestinal helminths in equids: Past, present and future.

This review is aimed to (i) appraise the literature on the use of molecular techniques for the detection, quantification and differentiation of gastrointestinal helminths (GIH) of equids, (ii) identify the knowledge gaps and, (iii) discuss diagnostic prospects in equine parasitology. Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines for systematic reviews, we retrieved 54 studies (horses: 50/54; donkeys and zebras: 4/54) from four databases. Polymerase chain reaction (PCR) was employed in all of the studies whereas PCR amplicons were sequenced in only 18 of them. Other techniques used (including modifications of PCR) were reverse line blot, quantitative (q)PCR, restriction fragment length polymorphism, nested-PCR, PCR-directed next-generation sequencing, Southern blotting, single strand conformation polymorphism, PCR-enzyme linked immunosorbent assay, matrix-assisted laser desorption/ionisation-time of flight and random amplification of polymorphic DNA. Most of the studies (53/54) used nuclear ribosomal RNA (including the internal transcribed spacers, intergenic spacer, 5.8 S, 18 S, 28 S and 12 S) as target loci while cytochrome c oxidase subunit 1 and random genomic regions were targeted in only three and one studies, respectively. Overall, to date, the majority of molecular studies have focused on the diagnosis and identification of GIHs of equids (i.e. species of Anoplocephala, Craterostomum, cyathostomins, Oesophagodontus, Parascaris, Strongylus, Strongyloides and Triodontophorus), with a recent shift towards investigations on anthelmintic resistance and the use of high-throughput nemabiome metabarcoding. With the increasing reports of anthelmintic resistance in equid GIHs, it is crucial to develop and apply techniques such as advanced metabarcoding for surveillance of parasite populations in order to gain detailed insights into their diversity and sustainable control. To the best of our knowledge, this is the first systematic review that evaluates molecular investigations published on the diagnosis and quantification of equid GIHs and provides useful insights into important knowledge gaps and future research directions in equid molecular parasitology.

Absence of Polymorphisms in Codons 167, 198 and 200 of All Seven ß-Tubulin Isotypes of Benzimidazole Susceptible and Resistant Parascaris spp. Specimens from Australia.

Benzimidazoles resistance is widespread in strongyle parasitic nematodes and associated with polym orphisms in the codons 167, 198 and 200 of isotype 1 ß-tubulin (tbb-1). In ascarids, benzimidazole (BZ) resistance has rarely been reported and in none of these cases were any of these polymorphisms detected. Here, available genome and transcriptome data from WormBase ParaSite were used to compare the complete ß-tubulin reservoirs of Parascaris univalens, Ascaris suum and Ascaris lumbricoides. Adult Parascaris spp. specimens collected in Australia from horses after BZ treatment (susceptible, n = 13) or surviving BZ treatment and collected after ivermectin treatment (resistant, n = 10) were genotyped regarding codons 167, 198 and 200 using Sanger sequencing. Phylogenetic analyses clearly showed that there are no one-to-one ascarid orthologs of strongyle tbb-1 genes. In the reference genomes, as well as phenotypically susceptible and resistant Parascaris spp. from Australia, six out of seven ß-tubulin genes showed a BZ-susceptible genotype (F167, E198, F200). The only exception were the testis-specific ß-tubulin D genes from all three ascarid species that encode tyrosine at codon 200. This was observed independently of the BZ-susceptibility phenotype of Parascaris spp. These data suggest that different mechanisms lead to BZ resistance in ascarid and strongyle nematodes.

Cyathostomin resistance to moxidectin and combinations of anthelmintics in Australian horses.

BACKGROUND: Cyathostomins are the most important and common parasitic nematodes of horses, with > 50 species known to occur worldwide. The frequent and indiscriminate use of anthelmintics has resulted in the development of anthelmintic resistance (AR) in horse nematodes. In this study we assessed the efficacy of commonly used anthelmintics against cyathostomins in Australian thoroughbred horses. METHODS: Two drug efficacy trials per farm were conducted on two thoroughbred horse farms in the state of Victoria, Australia. In the first trial, the horses on Farm A were treated with single and combinations of anthelmintics, including oxfendazole (OFZ), abamectin (ABM), abamectin and morantel (ABM + MOR), moxidectin (MOX) and oxfendazole and pyrantel (OFZ + PYR), at the recommended doses, whereas the horses on Farm B only received MOX, at the recommended dose. The faecal egg count reduction test (FECRT) was used to determine the efficacy and egg reappearance period (ERP) of anthelmintics. Based on the results of the first trial, the efficacies of MOX and a combination of ABM + MOR were reassessed to confirm their activities against cyathostomins. RESULTS: Of the five anthelmintic products tested on Farm A, resistance against OFZ, ABM and OFZ + PYR was found, with efficacies of - 41% (- 195% lower confidence limit [LCL]), 73% (60% LCL) and 82% (66% LCL) at 2 weeks post-treatment, respectively. The FECRT showed high efficacies of MOX and ABM + MOR (100%) at 2 week post-treatment and shortened ERPs for these anthelmintics (ABM + MOR: 4 weeks; MOX: 5 weeks). Resistance to MOX was found on Farm B, with a reduced efficacy of 90% (70% LCL) and 89% (82% LCL) at 2 weeks post-treatment in trials one and two, respectively. CONCLUSIONS: This study provides the first evidence of MOX- and multidrug-resistant (ABM and combinations of anthelmintics) cyathostomins in Australia and indicates the need for continuous surveillance of the efficacy of currently effective anthelmintics and large-scale investigations to assess the ERP for various anthelmintics.

Molecular detection of Strongyloides sp. in Australian Thoroughbred foals.

BACKGROUND: Strongyloides westeri is found in the small intestine of young horses, mainly in foals up to about 16 weeks of age. The main source of infection for foals is through transmammary transmission, and foals can develop acute diarrhoea, weakness, dermatitis and respiratory signs. The epidemiology of S. westeri in Australia is largely unknown. Further, molecular techniques have never been employed for detection of S. westeri in horses. This pilot study aimed to assess the utility of a molecular phylogenetic method for the detection of S. westeri in the faeces of foals. METHODS: Faecal samples were collected from a foal of less than 2 months of age, and eggs of Strongyloides sp. were detected using the modified McMaster technique. DNA was extracted from purified eggs, and a partial fragment of the small subunit of the nuclear ribosomal DNA (18S) was characterised using polymerase chain reaction, DNA sequencing and phylogenetic methods. RESULTS: Microscopic examination of faeces revealed small ellipsoidal eggs typical of Strongyloides sp. The 18S sequence generated by PCR in this study revealed 98.4% identity with that of a reference sequence of S. westeri available from GenBank. Phylogenetic analyses revealed a polyphyletic clustering of S. westeri sequences. CONCLUSION: This is the first study reporting the detection of DNA of Strongyloides sp. in faeces of a foal using a molecular phylogenetic approach targeting the variable region of 18S rDNA. It is anticipated that this study will allow future molecular epidemiological studies on S. westeri in horses.

Comparative studies on faecal egg counting techniques used for the detection of gastrointestinal parasites of equines: A systematic review.

Faecal egg counting techniques (FECT) form the cornerstone for the detection of gastrointestinal parasites in equines. For this purpose, several flotation, centrifugation, image- and artificial intelligence-based techniques are used, with varying levels of performance. This review aimed to critically appraise the literature on the assessment and comparison of various coprological techniques and/or modifications of these techniques used for equines and to identify the knowledge gaps and future research directions. We searched three databases for published scientific studies on the assessment and comparison of FECT in equines and included 27 studies in the final synthesis. Overall, the performance parameters of McMaster (81.5%), Mini-FLOTAC® (33.3%) and simple flotation (25.5%) techniques were assessed in most of the studies, with 77.8% of them comparing the performance of at least two or three methods. The detection of strongyle, Parascaris spp. and cestode eggs was assessed for various FECT in 70.4%, 18.5% and 18.5% studies, respectively. A sugar-based flotation solution with a specific gravity of ≥1.2 was found to be the optimal flotation solution for parasitic eggs in the majority of FECT. No uniform or standardised protocol was followed for the comparison of various FECT, and the tested sample size (i.e. equine population and faecal samples) also varied substantially across all studies. To the best of our knowledge, this is the first systematic review to evaluate studies on the comparison of FECT in equines and it highlights important knowledge gaps in the evaluation and comparison of such techniques.

Interobserver and intraobserver reliability for 2 grading systems for gastric ulcer syndrome in horses.

BACKGROUND: Grading of equine gastric ulcer syndrome (EGUS) is undertaken in clinical and research settings, but the reliability of EGUS grading systems is poorly understood. HYPOTHESIS/OBJECTIVES: Investigate interobserver and intraobserver reliability of an established ordinal grading system and a novel visual analog scale (VAS), and assess the influence of observer experience. ANIMALS: Sixty deidentified gastroscopy videos. METHODS: Six observers (3 specialists and 3 residents) graded videos using the EGUS Council (EGUC) system and VAS. Observers graded the videos three 3 for each system, using a cross-over design with at least 1 week between each phase. The order of videos was randomized for each phase. METHODS: Interobserver and intraobserver reliability were estimated using Gwet's agreement coefficient with ordinal weights applied (AC2) for the EGUC system and the intraclass correlation coefficient (ICC) for the VAS. RESULTS: Using the EGUC system, interobserver reliability was substantial for squamous (AC2 = 0.69; 95% confidence interval [CI], 0.57-0.80) and glandular mucosa (AC2 = 0.72; 95% CI, 0.70-0.75), and intraobserver reliability was substantial for squamous (AC2 = 0.80; 95% CI, 0.71-0.90) and glandular mucosa (AC2 = 0.80; 95% CI, 0.74-0.86). Interobserver reliability using the VAS was moderate for squamous (ICC = 0.64; 95% CI, 0.31-0.96) and poor for glandular mucosa (ICC = 0.35; 95% CI, 0.06-0.64), and intraobserver reliability was moderate for squamous (ICC = 0.74; 95% CI, 0.62-0.86) and glandular mucosa (ICC = 0.56; 95% CI, 0.39-0.72). CONCLUSIONS AND CLINICAL IMPORTANCE: The EGUC system had acceptable intraobserver and interobserver reliability and performed well regardless of observer experience. Familiarity and observer experience improved reliability of the VAS.

Intragastric pH of foals admitted to the intensive care unit.

BACKGROUND: Intragastric pH profiles of neonatal foals admitted to the intensive care unit (ICU) remain poorly characterized. HYPOTHESIS/OBJECTIVES: To determine intragastric pH profiles and clinical parameters associated with intragastric pH in foals admitted to the ICU. ANIMALS: Forty-two neonatal foals admitted to the ICU and requiring placement of an indwelling nasogastric tube for nutritional management were included. METHODS: Intragastric pH was measured for 24 hours from the time of admission. Mean pH, % time pH <4, and % time pH >4 were determined for each foal. History, clinical findings, and clinicopathological data recorded at the time of presentation were collected. RESULTS: The mean pH of included foals was 5.5 ± 1.8. The median % time pH <4 was 6.3% (range: 0-99). A history of placentitis was associated with greater mean pH (median 5.3 (range: 0.9-7.8) versus median 7.2 (5.9-11.3); P = .002) and less % time pH <4 (median 13 (0-99.6) versus median 0.1 (0-7.2); P = .01). Foals with diarrhea had a greater % time pH <4 (median 4.6% (0-99) versus median 28.8% (1.4-57.48); P = .02). Foals with a pH >4 for >50% recording time had a lower PaO2 (mean difference 25.0 mm Hg; 95% confidence interval [CI], 14.4-35.6; P = .03) and higher PaCO2 (mean difference 14.9 mm Hg; 95% CI, 4.7-25.2; P = .02). Surviving foals had a lower mean median hourly pH (P = .02). CONCLUSIONS AND CLINICAL IMPORTANCE: Intragastric pH profiles were unpredictable and mostly >4 for >80% of the recording time. This study does not support the indiscriminate administration of acid suppressive treatment.

A questionnaire study of parasite control in Thoroughbred and Standardbred horses in Australia.

BACKGROUND: Information regarding parasite control practices currently used on Thoroughbred and Standardbred studs in Australia is lacking. Anthelmintic resistance (AR) is a global problem which has implications for equine health and welfare. OBJECTIVES: To identify parasite control practices currently used on horse studs in Australia and investigate the frequency of use of management factors that have been associated with the likelihood of promoting or delaying AR. STUDY DESIGN: Questionnaire study of equine parasite control on Thoroughbred and Standardbred studs in Australia. METHODS: An online questionnaire was emailed to 300 studs in Australia. Information obtained included property details, grazing management, anthelmintic use, non-chemotherapeutic parasite control practices, use of faecal egg counts (FECs) and perceptions of AR. RESULTS: Seventy-five completed questionnaires were received (25% response rate). Macrocyclic lactones (MLs) were the most commonly administered anthelmintics in mares and foals and less than 5% of respondents used targeted treatment regimens. The implementation of pasture hygiene practices was variable. The majority of respondents (97%) considered AR to be important; however, few respondents were aware of the use of FEC reduction tests for monitoring of drug efficacy. MAIN LIMITATIONS: The potential for nonresponse bias was the main limitation of this study. CONCLUSIONS: Parasite control strategies on Australian stud farms remain over-reliant on anthelmintic use. The frequent use of MLs is of concern for the increased selection pressure for AR. There is a lack of awareness of the importance of non-chemotherapeutic strategies in integrated approaches to parasite control aimed at delaying the development of AR. This study highlights the need for greater veterinary involvement in the implementation of more sustainable parasite control practices with greater emphasis placed on surveillance through FEC testing.