Introduction
In Ireland, the Thoroughbred (TB) and Irish Sport Horse industries are a thriving part of the economy; approximately €1 billion was contributed to the Irish exchequer by the TB industry in 2012 (Dukes, Reference Dukes2009) and the Irish Sport Horse industry contributed €816 million in 2016 (Corbally and Fahey, Reference Corbally and Fahey2017). Horses can be infected with a range of gastrointestinal parasite species such as ascarids, tapeworms and strongyles. However, the small strongyles (cyathostomins) are considered the most important parasites in horses due to their ubiquity, prevalence and pathogenicity (Nielsen et al., Reference Nielsen, Fritzen, Duncan, Guillot, Eysker, Dorchies, Laugier, Beugnet, Meana, Lussot-Kervern and von Samson-Himmelstjerna2010b). Today, resistance to benzimidazoles (BZ) is highly prevalent and widespread in most countries (Kaplan and Vidyashankar, Reference Kaplan and Vidyashankar2012; Nielsen, Reference Nielsen2012) while pyrantel (PYR) resistance in cyathostomins is emerging in the USA, UK, Germany and Italy (Kaplan, Reference Kaplan2004; Traversa et al., Reference Traversa, von Samson-Himmelstjerna, Demeler, Milillo, Schurmann, Barnes, Otranto, Perrucci, di Regalbono, Beraldo, Boeckh and Cobb2009; Lester et al., Reference Lester, Spanton, Stratford, Bartley, Morgan, Hodgkinson, Coumbe, Mair, Swan, Lemon, Cookson and Matthews2013; Nielsen et al., Reference Nielsen, Vidyashankar, Hanlon, Diao, Petersen and Kaplan2013). Recently, resistance to ivermectin (IVM) and/or shortened egg reappearance period (ERP) of moxidectin (MOX) in cyathostomins have been reported in different parts of the world, such as the USA (Little et al., Reference Little, Flowers, Hammerberg and Gardner2003; Rossano et al., Reference Rossano, Smith and Lyons2010; Lyons et al., Reference Lyons, Tolliver, Collins, Ionita, Kuzmina and Rossano2011), Italy (Traversa et al., Reference Traversa, von Samson-Himmelstjerna, Demeler, Milillo, Schurmann, Barnes, Otranto, Perrucci, di Regalbono, Beraldo, Boeckh and Cobb2009), UK (Lester et al., Reference Lester, Spanton, Stratford, Bartley, Morgan, Hodgkinson, Coumbe, Mair, Swan, Lemon, Cookson and Matthews2013; Relf et al., Reference Relf, Lester, Morgan, Hodgkinson and Matthews2014), The Netherlands (van Doorn et al., Reference van Doorn, Eysker, Geurden, Ploeger, Kooyman and Wagenaar2014; Kooyman et al., Reference Kooyman, van Doorn, Geurden, Mughini-Gras, Ploeger and Wagenaar2016), Brazil (Molento et al., Reference Molento, Antunes, Bentes and Coles2008; Canever et al., Reference Canever, Braga, Boeckh, Grycajuck, Bier and Molento2013) and Finland (Nareaho et al., Reference Nareaho, Vainio and Oksanen2011). Frequent treatments, combined with underdosing are the main factors playing a role in the development of anthelminthic resistance (AR) (Nielsen et al., Reference Nielsen, Pfister and von Samson-Himmelstjerna2014a). Several surveys from various countries, including Ireland, the UK, the USA, Italy, Sweden and South Africa, have found that many horse owners rely strongly on the interval-dose principle with intensive and long-term use of macrocyclic lactones (Matthee et al., Reference Matthee, Dreyer, Hoffmann and van Niekerk2002; O'Meara and Mulcahy, Reference O'Meara and Mulcahy2002; Lind et al., Reference Lind, Rautalinko, Uggla, Waller, Morrison and Höglund2007; Relf et al., Reference Relf, Morgan, Hodgkinson and Matthews2012, Reference Relf, Lester, Morgan, Hodgkinson and Matthews2014; Lester et al., Reference Lester, Spanton, Stratford, Bartley, Morgan, Hodgkinson, Coumbe, Mair, Swan, Lemon, Cookson and Matthews2013; Bolwell et al., Reference Bolwell, Rosanowski, Scott, Sells and Rogers2015). Since a survey performed in 2002 (O'Meara and Mulcahy, Reference O'Meara and Mulcahy2002) there has been no investigation of helminth control practices on Irish horse farms. For this reason, a questionnaire survey was carried out on current helminth control practices used by horse owners in Ireland (Appendix 1). Data on helminth control practices by horse owners may pinpoint potential risk factors for AR.
Materials and methods
The questionnaire consisted of four parts: general information, grazing and pasture management, treatment strategies, and the use of fecal egg counts (FECs) in parasite control. Initially, a pilot questionnaire was sent to small number of establishments (n = 17) by email and based on feedback changes were made. In July 2014, a brief explanation of the survey was given to the members of the Irish Thoroughbred Breeders’ Association (ITBA) at meetings held across Ireland. Between August and October, the questionnaire was emailed to approximately 700 members of the ITBA and Irish Sport Horse industries with a link to an electronic copy of the questionnaire produced using Survey Monkey. In November 2014, 265 follow-up questionnaires were posted to ITBA members with an offer of free FEC analyses for up to 20 horse samples.
Data analysis
Data from the questionnaire were entered on Microsoft Excel (Microsoft Office, 2013), and analysed using IBM SPSS Statistics (Version 24, 2016). Descriptive statistics for each question were analysed. To determine the percentage responses to each question, missing data were excluded from the total number of responses. In the results, the total number of responses (n) are indicated for each percentage.
Results
General information
The response rate was relatively low with only 78 (11.14%, n = 700) questionnaires returned. Most of the respondents were located in the east (61%, n = 74) and the south (26%, n = 74) in Ireland, few responses were received from the west (8%, n = 74) and the north (5%, n = 74). The majority of responses (47.4%, n = 37), were received from establishments that did not indicate the type of farming enterprise, while 35 (44.9%) were from stud farms and six (7.7%) were from Sport Horse farms. Of the 78 respondents, only 25 (23%) completed the electronic questionnaire. Table 1 summarizes the different categories of horses present in the 78 establishments that responded to the questionnaire. The majority of respondents (71.8%, n = 71) stated that they did not observe any signs of clinical disease due to parasites during the previous year.
Table 1. Summary of the percentage and range of animal categories present on 78 horse farms in Ireland
Grazing and pasture management
Daily grazing, time ranged from 16 to 24 h per day during the summer and autumn (89%, n = 74 and 65%, n = 72, respectively), and 1 to 10 h per day during winter (Fig. 1). Less than half of respondents applied pasture rotation on a monthly basis (47%, n = 66) and harrowed or clipped pastures monthly or more frequently (44%, n = 69). The co-grazing by cattle and sheep was performed on a monthly, yearly and occasional basis on 27%, 22% and 21% farms (n = 71), respectively (Fig. 2). Only a few farms (37.6%, n = 75) removed feces from pasture with 26.7% (n = 75) removing feces infrequently (Fig. 3), 73% (n = 27) removed feces manually and 26% (n = 27) did it mechanically. Of the respondents, 22.2% (n = 72) kept horses off pasture for 7 days or less after treatment and almost half of the respondents (45.8%, n = 73) indicate that they move horses to clean pasture after treatment.
Fig. 1. The number of hours that horses spent grazing per day (h day−1) during different season as reported by respondents in Ireland (n = 74).
Fig. 2. Different pasture management strategies followed by Irish stud farmers (n = 71).
Fig. 3. Percentage and frequency at which respondents (n = 75) remove feces from pasture in an Irish survey.
Treatment strategies
More than two-thirds of the respondents (74.6%, n = 67) indicated that the owner/manager was responsible for administering anthelmintic while the rest (25.4%, n = 67) reported that the groom, veterinarian or nurse was responsible for this activity. Of the respondents, 65.7% (n = 70) sought veterinary advice on helminth control; however, only 23% (n = 67) of horse owners who treated horses followed the recommendation of a veterinarian. The majority of respondents (76%, n = 67) followed a set dosing programme, while only 3% treated at signs of disease. The majority of respondents (81.4%, n = 70) reported that they treated their horses 4–5 times a year, while 15.7% (n = 70) treated the horses on a monthly basis and 2.9% (n = 70) treated their horses only once or twice a year. Most respondents (71.8%, n = 71) stated that spring and autumn were critical times for treatment, followed by summer and the foaling period by 46.5% (n = 71) and 43.7% (n = 72) of studs, respectively. Half of owners (49.2%, n = 59) rotated between drug classes ⩾4 times per year, 35.6% (n = 59) rotated once or twice per year while 11.9% (n = 59) rotated infrequently between drug classes. Overall, IVM and MOX were the most commonly administered anthelmintic in 2014 by 80% and 71.8% of respondents (n = 71), respectively. BZ and PYR drugs were used by 53% and 35% of respondents (n = 71), respectively. Only one owner indicated that doramectin (Dectomax®) was used (Fig. 4). Veterinary advice and drug rotation appeared to be the most influential factors determining the choice of drug classes as indicated by 45 and 43%, of the respondents (n = 73), respectively. The price, drug effectiveness and own experience were less important factors (27.4%, 26% and 24.7%, respectively). Only a few of the respondents (17.8%, n = 73) considered the FECs to be an important factor in their choice of an anthelmintic (Fig. 5). Only a few owners (11.3%, n = 62) weighed each horse prior to treatment; the majority (74.2%, n = 62) only estimated the weight of the horses visually and 17.7% (n = 62) administered one tube/packet of the drug per animal (Fig. 6). A total of 41.7% (n = 72) of respondents stated that they performed FECs. However, the majority (64.5%, n = 31) performed FECs infrequently (>6 months), 22.6% (n = 31) performed FECs analysis more frequently (between 1–3 monthly intervals). The rest of the respondents (12.9%, n = 31) performed FECs related to signs of illness. Only 48% (n = 31) of responses appeared to be targeting treatment of horses based on FECs ⩾200 egg per gram. Although more than half of the respondents (50.1%, n = 69) reported that they were aware of the faecal egg count reduction test (FECRT), only 12.9% (n = 70) have performed this test in the past. Only four respondents stated that eggs were observed in the post-treatment samples. A few respondents (6%, n = 65) indicated that they had tested the efficacy of the drugs being used, however none of them considered AR as a problem on their farm. A total of 33 (42%, n = 73) respondents indicated that they received horses during 2014 but only 23 (31.5%) reported placing visiting horses in quarantine. Only four of these respondents (n = 23) had a quarantine period of 1–2 days, while the majority (73.9%, n = 23) had a quarantine period ⩾7 days. A large number (61.5%, n = 71) of respondents that received horses in 2014 reported that visiting horses were treated with either IVM or MOX on arrival. A high number of establishments (83.6%, n = 74) stated that foals were treated more frequently and with different anthelmintics than adult horses (59.5% and 39.2%, respectively). One-half of respondents (50.7%, n = 67) indicated that they started treating foals between 2 and 4 weeks of age and 29.8% (n = 67) of respondents emphasized a greater attention to dosing foals at 5–6 weeks of age (Fig. 7).
Fig. 4. Different anthelmintic drugs used by respondents (n = 71) in Ireland during 2014. IVM, ivermectin; MOX, moxidectin; BZ, benzimidazole; MOX/PRAZ, moxidectin and praziquantel; PYR, pyrantel; IVM/PRAZ, ivermectin and praziquantel, other (doramectin).
Fig. 5. Factors that influenced the choice of anthelmintic drugs used by respondents (n = 73) to treat horses in Ireland.
Fig. 6. The methods used by Irish horse owners (n = 71) to calculate the dose of an anthelmintic drug to be administered to horses.
Fig. 7. The age at which foals receive their first anthelmintic treatment on Irish horse farms (n = 67).
Discussion
Anthelmintic resistance is a threatening problem to the livestock industry and posing very serious threats to the future welfare and production of livestock throughout the world. Recently, several studies have been evaluating the control and management of gastrointestinal helminth (GIH) in horses in the UK and other countries in the EU (Matthee et al., Reference Matthee, Dreyer, Hoffmann and van Niekerk2002; Lind et al., Reference Lind, Rautalinko, Uggla, Waller, Morrison and Höglund2007; Relf et al., Reference Relf, Morgan, Hodgkinson and Matthews2012, Reference Relf, Lester, Morgan, Hodgkinson and Matthews2014; Lester et al., Reference Lester, Spanton, Stratford, Bartley, Morgan, Hodgkinson, Coumbe, Mair, Swan, Lemon, Cookson and Matthews2013; Bolwell et al., Reference Bolwell, Rosanowski, Scott, Sells and Rogers2015; Papini et al., Reference Papini, De Bernart and Sgorbini2015; Lester et al., Reference Lester, Morgan, Hodgkinson and Matthews2018). An intensive use of anthelmintic drugs, use of the same drug class and underdosing have been reported as the main factors contributing to the development of resistance in horse nematodes (Shalaby, Reference Shalaby2013). Knowledge regarding helminth control strategies of horses and donkeys in Ireland is limited and only one study has been published over 15 years ago (O'Meara and Mulcahy, Reference O'Meara and Mulcahy2002). The findings from our questionnaire survey reported critical information on helminth control strategies used on Irish equine farms. The response rate to the questionnaire was low, in contrast to the last survey in 2002 by O'Meara and Mulcahy (Reference O'Meara and Mulcahy2002) where 55% responses were received. However, several other studies have reported similar low response rate in their surveys (Joost et al., Reference Joost, Irwin and Good2002; Oppenheim, Reference Oppenheim2005; Relf et al., Reference Relf, Morgan, Hodgkinson and Matthews2012). A number of factors could have influenced the response rate including the length of the questionnaire; owners being unwilling to spend time completing long postal surveys, or unwilling to answer questions that require them to consult their records for factual information. From the survey, the respondents confirmed that they did not observe clinical disease associated with equine intestinal parasites. The largest number of responses came from stud farms in the east of Ireland where a high proportion of Irish TB stud farms are located. These responses were from large public stud farms to small individual enterprises. Control of helminth parasite infection in horses is an important element of applied management in the field. Good pasture management practices can reduce the incidence of clinical disease in horses (Relf et al., Reference Relf, Morgan, Hodgkinson and Matthews2013; Nielsen et al., Reference Nielsen, Pfister and von Samson-Himmelstjerna2014a, Reference Nielsen, Reinemeyer, Donecker, Leathwick, Marchiondo and Kaplan2014b, Reference Nielsen, Reist, Kaplan, Pfister, van Doorn and Becher2014c). Quarantine of newly arrived or visiting animals is considered important to decrease pasture contamination with resistant parasite populations (Eysker et al., Reference Eysker, van Doorn, Lems, Weteling and Ploeger2006). Within the present study, only four stud farms receiving visiting animals (n = 23) performed quarantine for 1–2 days. It is difficult to compare the attitude towards the implementation of quarantine because it is influenced by factors such as the number of animals, size of the farms and other infectious diseases. This is similar to other countries, such as the UK and Germany where there was a poor level of quarantine (Traversa et al., Reference Traversa, von Samson-Himmelstjerna, Demeler, Milillo, Schurmann, Barnes, Otranto, Perrucci, di Regalbono, Beraldo, Boeckh and Cobb2009; Fritzen et al., Reference Fritzen, Rohn, Schnieder and von Samson-Himmelstjerna2010; Relf et al., Reference Relf, Morgan, Hodgkinson and Matthews2012). Most of the participants (61.5%) treated visiting horses; this was similar to results from the UK (74%) (Relf et al., Reference Relf, Morgan, Hodgkinson and Matthews2012), and Scotland (89%) (Stratford et al., Reference Stratford, Lester, Morgan, Pickles, Relf, McGorum and Matthews2014) but more than in Swedish farms (38%) (Lind et al., Reference Lind, Rautalinko, Uggla, Waller, Morrison and Höglund2007). On the other hand, the majority moved the horses to clean pasture after treatment. Moving animals to clean pasture after treatment allows for the increase in contamination of these pastures with resistant strains after an anthelmintic treatment kills most or all of the susceptible helminths (Eysker et al., Reference Eysker, van Doorn, Lems, Weteling and Ploeger2006; De Graef et al., Reference De Graef, Claerebout and Geldhof2013). In summer and autumn, the infective stages of parasites on the pasture reaches their highest level; this leads to a high probability of helminth infection (Nielsen et al., Reference Nielsen, Kaplan, Thamsborg, Monrad and Olsen2007). In this study, the majority of horses had access for more than 11 h to pastures during these seasons which is similar to that in the UK (Relf et al., Reference Relf, Morgan, Hodgkinson and Matthews2012) and other European countries, including Denmark (Lendal et al., Reference Lendal, Larsen, Bjørn, Craven, Chriél and Olsen1998), Germany (Hinney et al., Reference Hinney, Wirtherle, Kyule, Miethe, Zessin and Clausen2011) and Italy (Papini et al., Reference Papini, De Bernart and Sgorbini2015). Less than half of Irish stud farms reported performing monthly rotation of pastures or resting pastures for a period of time. These measures are important to allow the reduction of infective larvae on the pasture.
Pasture harrowing and/or clipping and co-grazing by other livestock species during the year is considered important to reduce the level of parasite burdens on pasture. Co-grazing by other species allows sheep and/or cattle to ingest horse parasites. Almost all Irish horse owners (91.5%) used co-grazing by sheep and/or cattle during the year which is in agreement with previous findings by O'Meara and Mulcahy (Reference O'Meara and Mulcahy2002) who reported rotational or mixed grazing with ruminants was found to be practised by 71% of Irish establishments. This is in contrast to UK where 49% of stud farms implemented such practices (Relf et al., Reference Relf, Morgan, Hodgkinson and Matthews2012). Moreover, very few establishments used co-grazing in Denmark (Lendal et al., Reference Lendal, Larsen, Bjørn, Craven, Chriél and Olsen1998) and Italy (Papini et al., Reference Papini, De Bernart and Sgorbini2015). On the other hand, mixed grazing with ruminants has important implications for transmission of liver fluke or Trichostrongylus axei. In Ireland, Fasciola hepatica is a common trematode parasite in Irish livestock. A recent study in Ireland found that the prevalence of F. hepatica in horses was 9.5% (Quigley et al., Reference Quigley, Sekiya, Egan, Wolfe, Negredo and Mulcahy2017). A list of lines was mentioned in the last paragraph. Another study found that mixed grazing between ponies and sheep reduced strongylid infection but the prevalence of T. axei increased in the horses (Eysker et al., Reference Eysker, Jansen, Wemmenhove and Mirck1983, Reference Eysker, Jansen and Mirck1986).
Only a small number of owners (44%) applied harrowing and/or clipping of pastures on a regular basis. One possible explanation for the low uptake would be that the Irish environment is wet throughout the year making it difficult to perform pasture harrowing and/or clipping. This is in contrast to Germany where frequent clipping was used (Fritzen et al., Reference Fritzen, Rohn, Schnieder and von Samson-Himmelstjerna2010). In Sweden, clipping was also performed more frequently (76%) (Lind et al., Reference Lind, Rautalinko, Uggla, Waller, Morrison and Höglund2007). Removing feces in large establishments requires special equipment which is expensive and time consuming; however, on small-to-middle size establishments this can be performed manually which is considered beneficial in reducing worm burden on pastures. A study by Corbett et al. (Reference Corbett, Love, Moore, Burden, Matthews and Denwood2014) indicated that establishments removing feces experienced an approximate 20% reduction in FECs every month during the study period. Still, owners at Irish stud farms did not appreciate the benefits of picking up feces from pastures as indicated in this study. However, applying this practice has increased by 5% from since the previous study in 2002 (32%) (O'Meara and Mulcahy, Reference O'Meara and Mulcahy2002). In the UK, this was used by 75% (Relf et al., Reference Relf, Morgan, Hodgkinson and Matthews2012), South Africa (61%) (Matthee et al., Reference Matthee, Dreyer, Hoffmann and van Niekerk2002) and in Sweden (41%) (Lind et al., Reference Lind, Rautalinko, Uggla, Waller, Morrison and Höglund2007). However, Irish horse owners performed this management better than in Germany (10%) (Fritzen et al., Reference Fritzen, Rohn, Schnieder and von Samson-Himmelstjerna2010), Italy (5.3%) (Papini et al., Reference Papini, De Bernart and Sgorbini2015) and Brazil where feces are never removed (Martins et al., Reference Martins, Verocai, Correia, Melo, Pereira, Scott and Grisi2009).
Reports of AR in equine parasites are increasing across the world and this is presumably due to treatment practices traditionally based on frequent treatments, rapid rotation of drugs, incorrect dosing and little or no parasite surveillance. High frequency of treatments can result in the selection of resistance strains, especially when treatment intervals are equal to or shorter than either the parasite's prepatent period or the ERP (Lloyd et al., Reference Lloyd, Smith, Connan, Hatcher, Hedges, Humphrey and Jones2000; Coles et al., Reference Coles, Jackson, Pomroy, Prichard, von Samson-Himmelstjerna, Silvestre, Taylor and Vercruysse2006; Nielsen et al., Reference Nielsen, Reist, Kaplan, Pfister, van Doorn and Becher2014c). This traditional approach is still widely used in several countries (Lloyd et al., Reference Lloyd, Smith, Connan, Hatcher, Hedges, Humphrey and Jones2000; Relf et al., Reference Relf, Morgan, Hodgkinson and Matthews2012; Robert et al., Reference Robert, Hu, Nielsen and Stowe2015). Results from this and the previous survey (O'Meara and Mulcahy, Reference O'Meara and Mulcahy2002) confirmed that most of the horse owners are still basing helminth control on frequent treatments often more than four times a year despite the fact that no signs of clinical disease were observed and with little veterinary involvement in helminth control programmes.
Drug rotation has historically been recommended (Drudge and Lyons, Reference Drudge and Lyons1966) when the rotation was required to achieve effective control with the few drugs available at the time. Since a direct relationship has been shown between the frequency of treatment and AR (Kaplan and Nielsen, Reference Kaplan and Nielsen2010), but in the absence of scientific evidence to support that rotation delays/slows the evolution of resistance, drug rotation is no longer recommended (Lloyd et al., Reference Lloyd, Smith, Connan, Hatcher, Hedges, Humphrey and Jones2000; Kaplan and Nielsen, Reference Kaplan and Nielsen2010). The findings in this study were similar to the previous Irish survey (O'Meara and Mulcahy, Reference O'Meara and Mulcahy2002) and other studies from the UK (Lloyd et al., Reference Lloyd, Smith, Connan, Hatcher, Hedges, Humphrey and Jones2000; Relf et al., Reference Relf, Morgan, Hodgkinson and Matthews2012) where rapid rotation between drug classes was generally applied in the field.
Similar to other studies, IVM and MOX were the most common anthelmintics used in this study (Lendal et al., Reference Lendal, Larsen, Bjørn, Craven, Chriél and Olsen1998; Nielsen et al., Reference Nielsen, Monrad and Olsen2006; Martins et al., Reference Martins, Verocai, Correia, Melo, Pereira, Scott and Grisi2009; Relf et al., Reference Relf, Morgan, Hodgkinson and Matthews2012). Despite resistance to BZ having been confirmed throughout the world, it is still used by 50% of Irish establishments and 14.3% reported it as the most frequently used drug without any concern for efficacy or resistance. However, in the questionnaire, the question did not clarify if BZ was used as a single dose or 5-day larvicidal dose.
The correct dose should be used to prevent the development of AR. The calculation of the dose according to the body weight of each animal is critical to avoid underdosing (Nielsen et al., Reference Nielsen, Pfister and von Samson-Himmelstjerna2014a). A common cause for incorrect dosing is the use of inaccurate weight by estimating weight visually, which was reported in this study by 74.2% of respondents and in the previous Irish study by 60% of respondents (O'Meara and Mulcahy, Reference O'Meara and Mulcahy2002), which was similar in turn to other studies in Germany (94.4%) (Fritzen et al., Reference Fritzen, Rohn, Schnieder and von Samson-Himmelstjerna2010), Italy (57.85%) (Papini et al., Reference Papini, De Bernart and Sgorbini2015), South Africa (45%) (Matthee et al., Reference Matthee, Dreyer, Hoffmann and van Niekerk2002) and the UK (36%) (Relf et al., Reference Relf, Morgan, Hodgkinson and Matthews2012).
The FECs allow the quantification of gastrointestinal parasite eggs within horse feces. It is easy to perform and inexpensive. For more than two decades, adoption of parasite control strategies such as performance of regular FECs and treatment of horses that have consistently high counts has been recommended to prevent the development of AR (Nielsen et al., Reference Nielsen, Reist, Kaplan, Pfister, van Doorn and Becher2014c). Leaving horses with low FECs (<200 EPG) untreated will have little impact on the health of horses (Schneider et al., Reference Schneider, Pfister, Becher and Scheuerle2014). The small numbers of eggs shed may provide critical levels of refugia that will greatly dilute the contribution to pasture contamination with resistance populations. Such an approach will succeed in reducing selection pressure for resistance while improving overall parasite control (Nielsen, Reference Nielsen2015). Recent studies have shown that selecting horses for treatment based on FECs was successful in keeping the worm burden low with little clinical disease or development of resistance (Lloyd et al., Reference Lloyd, Smith, Connan, Hatcher, Hedges, Humphrey and Jones2000; Fritzen et al., Reference Fritzen, Rohn, Schnieder and von Samson-Himmelstjerna2010; Nielsen et al., Reference Nielsen, Baptiste, Tolliver, Collins and Lyons2010a; Relf et al., Reference Relf, Morgan, Hodgkinson and Matthews2013; Schneider et al., Reference Schneider, Pfister, Becher and Scheuerle2014). However, in the present study and other studies, this approach has not been adopted where the majority of owners are unwilling to adjust their treatment strategies and only rarely combined FECs with reduced or selective anthelmintic treatment. There also seems to be a lack of awareness of AR, where none of the respondents were concerned about AR and the efficacies of available drugs while only a few have implemented FECR tests. Half of the respondents initially administered anthelmintics to foals at 2–4 monthly intervals which are in agreement with studies conducted in the UK and Germany (von Samson-Himmelstjerna et al., Reference von Samson-Himmelstjerna, Traversa, Demeler, Rohn, Milillo, Schurmann, Lia, Perrucci, di Regalbono, Beraldo, Barnes, Cobb and Boeckh2009; Relf et al., Reference Relf, Morgan, Hodgkinson and Matthews2012). Typically, young horses have a higher prevalence of strongyle infections, due to less developed immunity related to age (Lloyd et al., Reference Lloyd, Smith, Connan, Hatcher, Hedges, Humphrey and Jones2000; von Samson-Himmelstjerna et al., Reference von Samson-Himmelstjerna, Traversa, Demeler, Rohn, Milillo, Schurmann, Lia, Perrucci, di Regalbono, Beraldo, Barnes, Cobb and Boeckh2009; Fritzen et al., Reference Fritzen, Rohn, Schnieder and von Samson-Himmelstjerna2010; Peregrine et al., Reference Peregrine, Molento, Kaplan and Nielsen2014).
Overall, the results in this study regarding management practices and treatment strategies to control parasites in Irish equines are similar to the results of O'Meara and Mulcahy (Reference O'Meara and Mulcahy2002). Both sets of results show that horses were treated on a regular basis and they frequently rotate between drug classes. IVM and MOX were the most common drug class used in the treatment of GIH in both these studies. In the previous report in Ireland, 40% of respondents weighing animals and calculated the dose according to the body weight (O'Meara and Mulcahy, Reference O'Meara and Mulcahy2002), while in the current study, only 11% of horse owners reported weighting their horses. There is a general lack of awareness on the part of horse owners of the need to do FECs prior to treatment of their horses. It is interesting to note that in the 2002 study 56% of respondents reported that they did carry out FECs responding to a perceived problem while in the present study this decreased to 41% of respondents carrying out FECs, of these 22.5% performed FECs examinations on a regular basis.
Taken together, these results indicate a greater need to educate horse owners on proper management practices and treatment strategies to control parasites and delay the development of AR in horses in Ireland.
Conclusions
The finding from this study illustrates that stud owners do not follow best practice with regard to parasite control. The evaluation of the factors influencing horse owners in their parasite control strategy showed that monitoring FECs was of minor importance and that intensive treatment (>4 times per year) was the most common dosing regimen followed often in conjunction with underdosing and rapid rotation of anthelmintics. The findings highlight the continuing need to educate owners on best practice with regard to parasite control.
Author ORCIDs
Nagwa Elghryani, 0000-0002-0843-4431
Acknowledgements
The authors acknowledge the assistance of Des Leadon from the Irish Equine Centre, the Veterinary Committee of the Irish Thoroughbred Breeders’ Association (ITBA) and UCD Veterinary Hospital for helping to distribute the questionnaires. Also, we would like to thank all the respondents of the questionnaires. The authors would also like to thank Zoetis for their assistance in the study.
Financial support
This study was supported by Libya Ministry of Higher Education and University of Benghazi.
Conflict of interest
None.
Ethical standards
Not applicable.
Appendix
