The implementation of measures against parasites is an important aspect of equine husbandry since these infections can adversely impact horse health and welfare. Strongyle parasites are commonly found in the large intestine of horses and can cause disease that ranges from ill-thrift to sudden death. As a result, these parasites are the primary reason that horses at pasture should be maintained on a regular deworming program. Until approximately 20 years ago, the large strongyles (particularly
A large amount of evidence has been accumulated in recent decades documenting the declining efficacy of all three broad-spectrum anthelmintic classes for cyathostomin control for use in horses (Kaplan
Due to the increasing resistance of gastrointestinal nematodes (GIN) to anthelmintic substances and the lack of new anthelmintic classes for use in horses, recommendations have been made to control equine parasites with improved sustainable management, with the emphasis on monitoring and targeted dosing based on faecal egg count (FEC) for individual farms and horses (von Samson-Himmelstjerna, 2012; Matthews
Using survey data from a questionnaire, the aim of this study was to identify the parasite control practices used on equine studs in Lithuania and investigate factors that may be associated with the development of AR.
The survey comprised 16 questions: seven open-ended and nine closed questions. The multiple-choice questions with subjective answers to each question were divided into sections to obtain information on demography, grazing management and worm control strategies, including the use of anthelmintic substances.
Contact details for Lithuanian stables were obtained from the Lithuanian Equestrian Federation (LEF) and the national database jok.lt. From each of these lists, horse establishments were randomly selected using slips of paper or numbers randomly generated by the computer. The questionnaire was posted to 71 horse establishments in 2020. To maximise the number of respondents, 28 stables (central part of Lithuania) were visited and the farmers interviewed personally, while 31 others were interviewed by phone and the remaining respondents did not agree to provide data. Responses were obtained from the stable owner or stable manager (person responsible for the stable’s internal activities). Each questionnaire was completed in full. The same investigator conducted all the surveys.
Descriptive statistics were calculated using Microsoft Excel® (2013). The answers to open-ended questions were checked and coded into categories where appropriate. The Wilson Chi-square test (showing how common the subject is in the population) or Fisher’s Exact Test was used for categorised variables. All the tests were considered to be statistically significant at P<0.05.
The research related to animals complied with all the relevant national regulations and institutional policies for the care and use of animals.
Overall, 97 % of respondents primarily used anthelmintics to control nematode infections in their horses. More than two thirds of the respondents (65 %, n=38) indicated that the owner was responsible for administering anthelmintics, while the remainder (25 %, n=15) reported that veterinarians or the stable manager (10 %, n=6) were responsible (p<0.005), (Table 1). Forty-eight percent (n=28) of the respondents referred to veterinary advice for helminth control, but only 27 % (n=16) of horse owners who treated their horses followed a veterinarian’s recommendations (p<0.05). In addition, 85 % (n=49) stated that they dewormed all the horses on their farm at the same time. Only three farms/studs/horse establishments (5 %) used a weighing tape for each horse prior to treatment; the majority of respondents (68 %, n=39) estimated the weight of the horses by eye and 26 % (n=15) administered one tube/packet of the drug per horse (p<0.05), (Table 1).
Number, percentage and confidence interval (95% CI) of anthelmintic selection and administration practices assessed by questionnaires (n=59) on intestinal worm control practices in horses in Lithuania.
Worm-control factor | Number | % | 95 % CI |
---|---|---|---|
Macrocyclic lactones ᵃ | 33 | 58 % | (45 – 70)* |
Benzimidazoles ᵇ | 10 | 19 % | (10 – 29)* |
Tetrahydropyrimidine ͨ | 14 | 24 % | (15 – 37)* |
Once | 2 | 4 % | (1 – 12)* |
Twice | 16 | 28 % | (18 – 41)* |
Three times | 4 | 7 % | (3 – 17)* |
Four times | 34 | 60 % | (47 – 71)* |
Seven times | 1 | 2 % | (0 – 9)* |
Weight tape, weight formula | 3 | 5 % | (2 – 14)* |
By eye | 39 | 68 % | (56 – 79)* |
One tube/packet per animal | 15 | 25 % | (17 – 39)* |
Stud farm owner | 38 | 65 % | (52 – 75)* |
Veterinarian | 15 | 25 % | (16 – 38)* |
Farm manager | 6 | 10 % | (5 – 21)* |
Every treatment | 15 | 26 % | (17 – 39) |
Every year | 23 | 41 % | (29 – 53) |
Every 2-3 years | 19 | 33 % | (23 – 46) |
Aware of FEC test | 21 | 36 % | (25 – 48)* |
FEC used | 10 | 18 % | (28 – 68)* |
Monitoring and disease diagnosis | 3 | 5 % | (11 – 60)* |
Detection of AR | 2 | 4 % | (6 – 51)* |
Selection of horses for treatment | 5 | 9 % | (24 – 76)* |
Aware of FECRT | 16 | 28 % | (17 – 40)* |
FECRT used | 5 | 9 % | (14 – 56)* |
*P value (p<0.05); ᵃactive substance ivermectin (including injectable ivermectin for cattle) and moxidectin; ᵇactive substance fenbendazole; ͨ active substance pyrantel embonate.
The number of anthelmintic treatments per year varied from one to seven, with an average of 4.5 times. The majority of respondents (60 %, n=34) reported that they treated their horses four times per year, while 28 % (n=16) treated them twice a year, and 2 % (n=1) seven times a year (p<0.05), (Table 1). Most of the respondents (93 %, n=53) stated that spring and autumn were critical times for treatment.
According to 81 % of the respondents, the main reason given for anthelminthic treatment was as a preventive measure, (Fig. 1), 12 % referred to clinical signs (diarrhoea 1 %, weight loss 1 %, colic 4 %, rough hair coat 4 %, tail rubbing 2 %), and only 7 % (n=4) gave the treatment following positive parasitological tests (Fig. 2). The most commonly used substances were ML (58 %) in different formulations (including injectable ivermectin for cattle), while THP (24 %) and BZ (19 %) were used more sporadically (p<0.05), (Table 1). Only 33 % claimed to alternate between these drug classes every two to three years, 41 % every year and 26 % every treatment (Table 1).
Twenty-one (36 %) respondents were aware of the FEC test, but only 18 % of respondents said that FECs were performed on their property (p<0.05). 5 % of respondents used FECs for monitoring and disease diagnosis, 4 % for detection of AR and 9 % for selection of horses for treatment (p<0.05). Sixteen respondents were aware of the FECRT test, but only five respondents indicated that FECRT had been performed on their property (p<0.05).
Additional measures for equine gastrointestinal parasites were commonly undertaken in 80 % (n=47) of the stables (p<0.005). Twenty-six percent of the stud farms carried out more than one of the improvement procedures listed in Table 2. In all, 85 % (n=40) removed excrement from the stables and pasture (20 % of those stated that they did this at least once per week, 38 % at least once per month, 30 % once per quarter and 13 % once per year), 56 % mowed their pasture and 31 % practised mixed or rotational grazing with other species, i.e. cattle or sheep.
Number, percentage and confidence interval (95% CI) of combinations of pasture management practices assessed by questionnaires (n=59) on intestinal worm control practices in horses in Lithuania.
Pasture management practices | Number | % | 95 % CI |
---|---|---|---|
12 | 20 % | (12 – 32)* | |
47 | 80 % | (68 – 88)* | |
40 | 85 % | (72 – 93)* | |
at least once per week | 8 | 20 % | (11 – 35) |
at least once per month | 15 | 38 % | (24 – 53) |
at least once per quarter | 12 | 30 % | (18 – 45) |
once per year | 5 | 12 % | (6 – 26) |
15 | 31 % | (20 – 46)* | |
28 | 56 % | (45 – 72)* |
*P value (p<0.05)
This study is the first report on equine parasite control practice at a national level in Lithuania. Given that the response rate was relatively high (83 %) and respondents were from different parts of Lithuania, it is reasonable to assume that the results reflected parasite control practices over a broad geographical area. The high response rate may have been influenced by several factors including the short, structured questionnaire, telephone calls or direct contact to gather information, free FEC testing offered to stud farms, horse stables/farms, and advice and direct, constructive communication during visits.
According to the results of the present study, a positive FEC (diagnostic test) was ranked among the participants as the rarest reason for deworming horses (Fig. 1). Similarly, as in previous studies (Osterman
The survey from Lithuania revealed that 97 % of all equine operations dewormed at least once a year, with 60 % deworming four times or more and 26 % using drug rotation every treatment. Such intensive treatment frequency should be a matter of concern, since a direct relationship has been shown between the frequency of treatment and the rate of AR development (Uhlinger
Equine establishments in Italy treat horses at 4 – 8 week intervals with rapid drug rotation all year round (Papini
One of the risk factors in the development of AR is an inaccurate dose of the anthelmintic drug (Graef
This study confirms that the overwhelming majority of respondents rely on ML for equine parasite control (Tabel 1), which is in agreement with several other recent surveys (Wilkes
As 74 % of the respondents stated that their horses had access to grazing areas, usually permanent pastures, it can be concluded that the conditions on Lithuania horse farms are favourable for the transmission of pasture-borne strongyles. In countries with moderate temperatures, such as Lithuania, strongyle eggs and larvae may survive over winter.
Among the respondents, 80 % paid attention to the prevention of parasitic infections during the pasture period. Pasture maintenance mainly involved faecal removal, but only 20 % stated that they did this at least once per week, while 38 % did so once per month (Table 1). This is considerably lower than has been reported in the UK, where 49 % of respondents of a survey stated that they collected faeces at least once per week (Lloyd
The results of this study indicate that parasite control strategies on Lithuanian stud farms are currently still over-reliant on anthelmintic use. In an effort to preserve anthelmintic efficiency and reduce the risk of the development of AR, parasite control strategies are required. These should include a greater emphasis on monitoring through FEC testing, the integration and expansion of pasture hygiene practices, reduced anthelmintic use in order to preserve parasite refugia, and effective veterinary advice for the implementation of sustainable parasite control practices.