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Maternal recognition of pregnancy (MRP) is a process by which an early conceptus signals its presence to the maternal system and prevents the lysis of the corpus luteum, thus ensuring a maternal milieu supportive of pregnancy continuation. It is a fundamental aspect of reproductive biology, yet in the horse, the mechanism underlying MRP remains unknown. This review seeks to address some of the controversies surrounding the evidence and theories of MRP in the equine species, such as the idea that the horse does not conform to the MRP paradigm established in other species or that equine MRP involves a mechanical, rather than chemical, signal. The review examines the challenges of studying this particularly clandestine phenomenon along with the new tools in scientific research that will drive this quest forward in coming years, and discusses the value of knowledge gleaned along this path in the context of clinical applications for improving breeding outcomes in the horse industry. [ABSTRACT FROM AUTHOR]

Theileria equi, an intraerythrocytic protozoan parasite, causes equine piroplasmosis, a disease which negatively impacts the global horse industry. Genetic manipulation is one of the research tools under development as a control method for protozoan parasites, but this technique needs to be established for T. equi. Herein, we report on the first development of a stable transgenic T. equi line expressing enhanced green fluorescent protein/blasticidin S deaminase (eGFP/BSD). To express the exogenous fusion gene in T. equi, regulatory regions of the elongation factor-1 alpha (ef-1α) gene were identified in T. equi. An eGFP/BSD-expression cassette containing the ef-1α gene promoter and terminator regions was constructed and integrated into the T. equi genome. On day 9 post-transfection, blasticidin-resistant T. equi emerged. In the clonal line of T. equi obtained by limiting dilution, integration of the eGFP/BSD-expression cassette was confirmed in the designated B-locus of the ef-1α gene via PCR and Southern blot analyses. Parasitaemia dynamics between the transgenic and parental T. equi lines were comparable in vitro. The eGFP/BSD-expressing transgenic T. equi and the methodology used to generate it offer new opportunities for better understanding of T. equi biology, with the add-on possibility of discovering effective control methods against equine piroplasmosis. [ABSTRACT FROM AUTHOR]

BACKGROUND: Equine superficial digital flexor (SDF) tendonitis is a very common cause of lameness in athletic horses inducing long lameness and prolonged recovery. Multiple treatment protocols have been proposed for this injury none of which have been able to solve the problem completely. Therefore, an affordable, widely available, and non-invasive therapeutic protocol is sought in the horse industry. OBJECTIVES: The present study aimed to compare the use of topical dimethyl sulfoxide (DMSO) with a combination of topical DMSO and pulsed electromagnetic field (PEMF). METHODS: The subjects were divided into two groups of five polo ponies. The animals in the control group were treated by topical DMSO and controlled exercise, while the ponies in the experiment group received the same protocol plus PEMF on the injured tendon. RESULTS: The ultrasonographic factors evaluated in the current study were mostly similar between the two groups except for fiber alignment and echogenicity. The latter variables were shown to have a slightly better improvement in the test group indicating the minimal positive effects of PEMF. In clinical evaluation, both groups were almost identical suggesting no impacts for PEMF. CONCLUSIONS: In conclusion, applying PEMF using different protocols, such as more extended application at different frequencies is deemed necessary to elicit a favorable outcome of PEMF for the treatment of SDF tendonitis. [ABSTRACT FROM AUTHOR]

The National Equine Forum held in Westminster highlighted the importance of equine identification, traceability, and disease monitoring in the equine sector. The government aims to strike a balance with the live export of horses, preventing exports for slaughter while not burdening legitimate transport. A government consultation on improving equine ID and traceability was held in 2022, and new legislation is currently being drafted. The industry has expressed frustration with slow legislative progress but believes that once the legislation is in place, it will open up opportunities for the industry. [Extracted from the article]

Anthelmintics are commonly used in the equine industry to reduce parasite load, but there is a growing concern about anthelmintic resistance, especially in young horses where there is limited information available. Twenty-four, 2-yr-old Quarter Horses (825 ± 21 d of age, initial BW 409 ± 6 kg, 12 fillies and 12 geldings) originating from a single herd were used in a 42-d study to investigate the effectiveness of a commercial anthelmintic (fenbendazole) on fecal egg counts (FEC), hypothesizing that there would be a decrease in FEC following anthelmintic administration. Horses were housed individually (3.7m x 11m) and offered ad libitum Coastal Bermudagrass hay and water and fed a pelleted concentrate offered at 0.75% (as-fed) of their BW. During the 42-d study, BW was obtained and BCS were assigned in 21-d intervals. Fenbendazole was administered orally on d 0 and 14 dosed on BW per manufacturer label. Fresh fecal samples were collected on d 0 and 14, before anthelmintic administration, and on d 28 and 42. Fecal egg floats were conducted using the Modified Wisconsin Method, and eggs per gram (EPG) were determined in duplicate. A fecal egg count reduction test (FECRT) was calculated, beginning on d 14. Outliers were determined as values ± 2 standard deviations of the mean, and data were analyzed using PROC MIXED of SAS (v9.4) with the main effect of time. Horses increased in BW (P ≤ 0.01) over time, but BCS did not change (P = 0.25). Mean FEC increased over time (P ≤ 0.01), beginning on d 14, and remained increased to d 42 compared to baseline. However, there was a trend (P = 0.07) for mean FEC to be less on d 42 (189.70 ± 29 EPG) when compared with d 14 (251 ± 28 EPG). The calculated reduction of FEC were below the targeted 95% or greater and included d 14 (1.04%), d 28 (35%), and d 42 (41%). The increased shedding of eggs did not negatively impact BW or BCS. However, we reject the hypothesis since FEC increased following an-thelmintic treatment, indicating the need for consistent monitoring of anthelmintic efficacy in young horses. [ABSTRACT FROM AUTHOR]

The article presents the discussion on Equine piroplasmosis (EP) is a blood-borne protozoal infection primarily transmitted by ticks in horses and other equids. Topics include import conditions for horses include pre-import testing for EP and further testing during onshore quarantine as required; and requirements for Australian horses, perform field surveillance and investigate suspected disease cases more effectively and more efficiently.

The article presents the discussion on Bain Fallon Young Member Scholarships provides an opportunity for four Equine Group Young Members to attend our flagship event free of charge. Topics include scholarship is open to current financial Equine Group Young Members who can demonstrate outstanding ability and commitment to their profession and the horse industry; and intention to further develop and continue career opportunities in the equine veterinary profession.

• gB, gD, gH and gL glycoproteins are required and sufficient for EHV-1 PV cell entry. • EHV-1 specific antibodies are measurable in a pseudotype virus neutralisation assay. • Lyophilisation can be used for stable storage and transport of EHV-1 pseudotypes. Infection with equid herpesvirus 1 (EHV-1), a DNA virus of the Herpesviridae family represents a significant welfare issue in horses and a great impact on the equine industry. During EHV-1 infection, entry of the virus into different cell types is complex due to the presence of twelve glycoproteins (GPs) on the viral envelope. To investigate virus entry mechanisms, specific combinations of GPs were pseudotyped onto lentiviral vectors. Pseudotyped virus (PV) particles bearing gB, gD, gH and gL were able to transduce several target cell lines (HEK293T/17, RK13, CHO-K1, FHK-Tcl3, MDCK I & II), demonstrating that these four EHV-1 glycoproteins are both essential and sufficient for cell entry. The successful generation of an EHV-1 PV permitted development of a PV neutralisation assay (PVNA). The efficacy of the PVNA was tested by measuring the level of neutralising serum antibodies from EHV-1 experimentally infected horses (n = 52) sampled in a longitudinal manner. The same sera were assessed using a conventional EHV-1 virus neutralisation (VN) assay, exhibiting a strong correlation (r = 0.82) between the two assays. Furthermore, PVs routinely require -80 °C for long term storage and a dry ice cold-chain during transport, which can impede dissemination and utilisation in other stakeholder laboratories. Consequently, lyophilisation of EHV-1 PVs was conducted to address this issue. PVs were lyophilised and pellets either reconstituted immediately or stored under various temperature conditions for different time periods. The recovery and functionality of these lyophilised PVs was compared with standard frozen aliquots in titration and neutralisation tests. Results indicated that lyophilisation could be used to stably preserve such complex herpesvirus pseudotypes, even after weeks of storage at room temperature, and that reconstituted EHV-1 PVs could be successfully employed in antibody neutralisation tests. [ABSTRACT FROM AUTHOR]

Equine herpesvirus type 1 (EHV-1) is an alphaherpesvirus related to pseudorabies virus (PRV) and varicella-zoster virus (VZV). This virus is one of the major pathogens affecting horses worldwide. EHV-1 is responsible for respiratory disorders, abortion, neonatal foal death and equine herpes myeloencephalopathy (EHM). Over the last decade, EHV-1 has received growing attention due to the frequent outbreaks of abortions and/or EHM causing serious economical losses to the horse industry worldwide. To date, there are no effective antiviral drugs and current vaccines do not provide full protection against EHV-1-associated diseases. Therefore, there is an urgent need to gain a better understanding of the pathogenesis of EHV-1 in order to develop effective therapies. The main objective of this review is to provide state-of-the-art information on the pathogenesis of EHV-1. We also highlight recent findings on EHV-1 immune evasive strategies at the level of the upper respiratory tract, blood circulation and endothelium of target organs allowing the virus to disseminate undetected in the host. Finally, we discuss novel approaches for drug development based on our current knowledge of the pathogenesis of EHV-1. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Veterinary Journal / Revue Vétérinaire Canadienne is the property of Canadian Veterinary Medical Association and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The equine industry is an established part of Maryland agriculture with 79,100 equines valued at approximately $714 million in the state; approximately 10% of these animals are housed in one county. Equine operators are a unique demographic in the agricultural realm, because they are not managing land to produce food or fiber and often are employed in other professions unrelated to agriculture. These operators tend to be unaware of land conservation practices and can have a detrimental effect on areas, like the Chesapeake Bay economy and ecosystem, if shared resources are exploited. The purpose of this study was to explore equine operators' knowledge and connection of conservation best management practices (BMPs) and their role in being a caretaker of the land. The study was informed by the diffusion of innovations theory and gathered data through semi-structured, qualitative interviews. Equine operators in the study were found to use a variety of informational sources, had a high level of adoption of the BMPs they used, and overall, a majority of participants saw their role as caretakers of the land as an important aspect of their environmental actions. Recommendations from this research include improving communication processes to increase the spread of BMPs and adjusting specific infrastructure aspects to improve retention of equine operators practicing conservation efforts. Further research should investigate other niche areas of agriculture that could potentially be struggling with a knowledge deficit of BMPs and communication neglect between conservation offices and audiences. [ABSTRACT FROM AUTHOR]

The Swedish equine sector is considered a high-risk work environment, with relatively high injury rates and high severity of injuries. General safety research has identified a correlation between the safety performance and safety culture, but little is known about the intricacies of the safety culture in the Swedish equine sector, especially concerning managers’ and employees’ perceptions of their work environment. The safety climate assessment is recognised as an effective tool for identifying potential problems in the workplace, thus enhancing safety behaviour and decreasing the frequency and severity of injuries. The aim was to evaluate the safety climate at riding schools and trotting stables through the Nordic Safety Climate Questionnaire (NOSACQ-50) diagnostic tool, and to get a better understanding of the workers’ perceptions regarding safety and safety management at their workplace through complementary interviews. The results showed that the safety climate was generally positive and that employees were aware of the risks relating to their work. Riding schools commonly had routines in place for risk assessment and work environment management, but such routines were often lacking at trotting stables, indicating inadequate prioritisation of safety by the management. The main area that should be targeted to improve safety in the sector is employees’ prioritisation and non-acceptance of risks. Proactive instead of reactive safety management should be promoted, where safety is an integral part of daily work and all employees are encouraged to identify factors contributing to occupational injuries and develop strategies for injury prevention.

During the past 20 years, there has been a contraction in the New Zealand Thoroughbred industry and, to a lesser extent, within the Standardbred industry. These changes have seen an increasing proportion of the market being associated with fewer larger commercial farms. Many of these farms manage their own mares, and the mares and foals of several clients. This, in turn, has increased the similarity of the management of breeding and young stock within New Zealand. The temperate climate allows the majority of the management of breeding and young stock to be pasture based. The predominant pasture is ryegrass-clover mix that has been demonstrated to provide adequate nutrition for growth and development. The temperate climate also permits management of horses at pasture year round, which is proposed to stimulate development of the musculoskeletal system. Apart from a brief period during weaning, most young stock remain at pasture from birth until the start of yearling preparation. Free access to pasture exercise provides the opportunity to stimulate the musculoskeletal system for the future challenges as a racehorse. The export focus of many of the equine industries heavily influences the management decisions. Despite the availability of good-quality pasture post-weaning, many foals receive up to 50% of the daily dietary energy requirement as concentrates, possibly reflecting the emphasis on early sales as yearlings and the drive to optimise growth. The observations of drench resistance of common internal parasites presents an emerging problem for pasture-based production systems. Alarge proportion of the Thoroughbred foal crop is exported as yearlings or ready to run 2-year-olds. There is an increasing trend for Standardbreds to be sold as yearlings and this has resulted in changes in the management of Standardbred young stock. [ABSTRACT FROM AUTHOR]

Optimising the developmental potential of immature equine oocytes and in vitro -produced (IVP) embryos was explored through modifications of established media and holding temperature. In Experiment 1, delaying spontaneous resumption of meiosis through the process of simulated physiological oocyte maturation with the addition of the adenylate cyclase activator forskolin (50 µM) and the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (100 µM) to overnight holding medium before maturation improved blastocyst production (P < 0.05). In Experiment 2, the blastocyst production rate was increased significantly when cumulin (100 ng mL−1) was added to the overnight holding or culture media (P < 0.05). In Experiment 3, immature oocytes held overnight at 16°C before maturation had improved developmental competence than those held at 20°C and 5°C (P < 0.05). There was no difference between maturation rates, but blastocyst formation per cleaved oocyte was significantly greater in oocytes held overnight at 16°C than at 20°C or 5°C. Furthermore, blastocyst formation per recovered oocyte and per fertilised oocyte was greater when oocytes were held before maturation at 16°C than at 5°C (P < 0.05). In Experiment 4, the addition of sodium ascorbate (AC; 50 µg mL−1) to the maturation and/or culture media of oocytes and IVP embryos did not improve blastocyst production, but did appear to lower cleavage rates compared with oocytes and embryos cultured without AC. Successful in vitro production (IVP) of equine embryos requires meticulous incubation conditions for both overnight holding and maturation of immature oocytes. Developmental competence can be improved by holding temperature as well as media alternatives that regulate the resumption of meiosis and support cleavage and blastocyst production. As the horse breeding industry requests IVP embryos to preserve valuable genetic lines, these improvements may optimise the outcome of embryos produced in vitro. [ABSTRACT FROM AUTHOR]

Horses are exposed to various kinds of medication, however, there are limited determinations of plasma clearance (CLp) for the drugs used due to the high cost of equine in vivo studies. Many of the CLp values generated come from the equine sports industry for determining drug plasma screening limits in the control of medications at the time of competition. The kinetics of omeprazole metabolism were investigated in freshly isolated and cryopreserved equine hepatocytes and hepatic microsomes (n = 3 horses). The Vmax, Km and intrinsic clearance (CLint) of omeprazole were determined via the substrate depletion method as well as Km values for the formation of three metabolites. The CLint values were extrapolated to in vivo hepatic plasma clearance (CLH) using the well stirred and parallel tube models. Clp for omeprazole was successfully predicted using freshly isolated or cryopreserved equine hepatocytes, while microsomes under-predicted. Equine microsomes were used to perform a drug-drug interaction (DDI) study between omeprazole and chloramphenicol. The average inhibitor constant Ki, assuming competitive inhibition, was 15.4 ± 5 µM. To the authors' knowledge, this is the first report showing the successful extrapolation of drug CLp in the horse using equine hepatocytes and the prediction of a DDI using microsomes. [ABSTRACT FROM AUTHOR]

The COVID-19 pandemic and resulting stay-at-home directives, adopted out of necessity to protect human health, introduced significant challenges for horse owners and small equine businesses. Restricted access, and in many cases closure of barns, resulted in a multitude of questions and concerns within the equine community which needed to be addressed rapidly. Extension Horses, Inc. (EH) coordinated the development and delivery of a variety of educational resources utilizing a combination of online formats and dissemination through social media and EH member contact lists. A series of infographics, webinars, and podcasts (three in each category) were created to provide guidance on essential care of horses, emergency preparedness, financial assistance, legal concerns, and biosecurity during the crucial, initial weeks of the pandemic (March to April 2020). Web conferencing technology (Zoom) was used to facilitate discussion and task delegation among EH members and to conduct and record webinars and podcasts. Podcasts were hosted on Buzzsprout and infographics were created using Adobe InDesign. Live webinar participants were invited to participate in several polls during the webinar and were sent a brief survey to complete at the end of the webinar series. Analytics for all educational resources combined demonstrated a 32-d total direct reach of 135,563. Most live webinar participants identified themselves as horse owners and small equine business owners (55%). The majority of live webinar participants indicated the information was useful (99%), and they would utilize the resources they had learned about (80%). Survey respondents reported that Facebook, email, and word of mouth were key ways in which they learned about the webinars. The same survey found that the web-platform was an effective method to receive information (85% high satisfaction) and respondents were highly likely to recommend future EH webinars to others (88%). The three infographics had a total Facebook reach of 131,765, the webinars had 3,522 total views, and the three podcasts had 276 total downloads. The rapid response of EH and quick turnaround of products allowed a large online audience to receive vital information for coping with COVID-19. Having the established EH network, already familiar with virtual education, was a big asset in this effort. This can serve as a model for cooperative extension to utilize in future collaborative responses to industry issues. [ABSTRACT FROM AUTHOR]

Copyright of Iranian Journal of Veterinary Medicine is the property of University of Tehran and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Eye temperature assessed with infrared thermography is an adequate tool for stress level assessment in sport horses' competitions having a moderate heritability. Serotonin and dopamine signal transduction-linked gene variants have been associated with anxiety-related traits in several species. In this study we examined the association between 10 gene variants in BDNF , COMT , HTR1A , TPH2 and SLC6A4 genes (and the haplotypes at SLC6A4 gene) with stress level (measured with eye temperature and heart rate) in 270 animals, 135 Spanish Trotter Horses (STH) participating in trotting races and 135 'Pura Raza Español' (PRE) horses in dressage. Association analyses were performed using a unified mixed model (counting for population structure and individual relatedness) for the whole population and for each horse breed. The g.43865600G > A intronic gene variant located 11.0 kb downstream from the transcription start site of SLC6A4 gene was associated with an increase in eye temperature before competition with a relative contribution of this gene variant of 38.8% (P = 0.001), 31.8% just after (P = 0.001) and 29.8% 2 h after the competition (P = 0.003). In STH, the g.43865600G > A gene variant showed the same association with eye temperature before (P = 0.001, contribution 27.2%), just after (P = 0.0003, 29.0%) and after the competition (P = 0.002, 17.5%); and the c. * 111G > A gene variant located at the 3′UTR region of COMT gene was associated with eye temperature 2 h after the competition (P = 0.001, 22.3%). These results showed that SLC6A4 and COMT gene variants are associated with stress level measured as eye temperature increase during competitions, and may be promising tools for genetic testing against resistance at high stress levels in trotter horses. The Spanish horse industry represents the 0.5% of Spanish Gross National Product, in which the Pura Raza Español has an annual economic impact of ~$1200 million, and the Spanish Trotter Horse of $42 million. It has been confirmed that a horse's sporting performance is influenced by their stress level. This work aims to evaluate the stress level and the possible association with behaviour candidate genes, allowing the pre-selection of animals, reducing the training costs and increasing their genetic progress. [ABSTRACT FROM AUTHOR]

Marked changes in equine breeding technologies have occurred over the past 25 years. Although there have been numerous reviews on assisted reproduction techniques for horses, few publications include the acceptance and impact of these techniques on the horse industry. In this review, several techniques are discussed, with an emphasis on how they developed in the horse industry and altered equine reproductive medicine. Embryo transfer has become a widely used technology, allowing multiple foals to be produced per year. Embryos can be collected, cooled or frozen, and shipped to a distant facility for transfer into recipient mares. Failure to obtain embryos from some mares stimulated the development of oocyte collection and transfer. Oocyte technologies became more practical when intracytoplasmic sperm injection was developed in the early 2000s. There are now facilities across the world that routinely produce embryos in vitro. Cryopreservation of oocytes has lagged because of limited success, but embryo cryopreservation is commonplace. Techniques such as sex-sorted semen, superovulation and genetic diagnosis of embryos are not widely used, and they will require more development before they are established in the horse industry in a cost-efficient manner. In the past 25 years, there has been a vast expansion in the development of assisted reproduction techniques for the horse. This review focuses on the integration of these new techniques into the horse industry. Procedures such as embryo transfer, oocyte transfer and intracytoplasmic sperm injection are widely used, but other techniques, such as sexed semen and preimplantation genetic diagnosis, have been slower to be adopted. [ABSTRACT FROM AUTHOR]

Assisted reproduction techniques (ARTs) have become widespread in the equine breeding industry. In particular, the combination of oocyte recovery from live mares followed by IVM and intracytoplasmic sperm injection (ICSI) has increased markedly among the ARTs used with valuable or low-fertility animals. There is currently no consensus among research groups regarding the optimal oocyte maturation period to produce high-quality embryos. In this study, we report the maturation dynamics of equine oocytes at different time points, from 20 to 40 h (Experiment 1). In addition, in Experiment 2, equine ICSI blastocysts were produced from oocytes that exhibited early (up to 24 h) or late (28–30 h) extrusion of the first polar body (PB). Blastocyst rates and diameter were recorded and embryo quality was assessed by analysing the number of apoptotic cells and Yes-associated protein 1 (YAP1) expression. By 20 h of IVM, 42% of oocytes were mature, and the remaining oocytes matured within the next 17 h of IVM. Although no differences were found in cell apoptosis or the number of YAP1-positive cells between groups exhibiting early and late PB extrusion, embryos from the early group (Group I) exhibited an improved total cell number and blastocyst rate compared to embryos from the late group (Group II) (18.60% vs 10.17% respectively). Intracytoplasmic sperm injection is now a widespread technology used in the equine breeding industry. In order to improve embryo production, this study describes the nuclear maturation dynamics of equine oocytes. In this study, oocytes that matured early showed an improved blastocyst rate. Furthermore, oocytes that matured late also produced potentially viable blastocysts, although at a lower rate. [ABSTRACT FROM AUTHOR]

Epigenetic perturbations during the reprogramming process have been described as the primary cause of the low efficiency of somatic cell nuclear transfer (SCNT). In this study, we tested three strategies targeting nuclear reprogramming to investigate effects on equine SCNT. First, we evaluated the effect of treating somatic cells with chetomin, a fungal secondary metabolite reported to inhibit the trimethylation on histone 3 lysine 9 (H3K9 me3). Second, caffeine was added to the culture medium during the enucleation of oocytes and before activation of reconstructed embryos as a protein phosphatase inhibitor to improve nuclear reprogramming. Third, we tested the effects of the histone deacetylase inhibitor trichostatin A (TSA) added during both activation and early embryo culture. Although none of these treatments significantly improved the developmental rates of the in vitro aggregated cloned equine embryos, the first equine cloned foal born in Australia was produced with somatic cells treated with chetomin. The present study describes the use of chetomin, caffeine and TSA for the first time in horses, serving as a starting point for the establishment of future protocols to target epigenetic reprogramming for improving the efficiency of equine cloning. Cloning is an expensive and inefficient process, but has gained particular interest in the equine industry. In this study we explored different strategies to improve cloning efficiency and produced the first cloned foal born in Australia. Our data serve as a starting point for the establishment of future protocols for improving equine cloning efficiency. Cloning is an expensive and inefficient process, but has gained particular interest in the equine industry. In this work we explored different strategies to improve cloning efficiency and we produced the first cloned foal born in Australia. Our data serves as a starting point for the establishment of future protocols for improving equine cloning efficiency. [ABSTRACT FROM AUTHOR]

Equine herpesvirus-1 (EHV-1) is one of the most important and prevalent viral pathogens of horses and a major threat to the equine industry throughout most of the world. EHV-1 primarily causes respiratory disease but viral spread to distant organs enables the development of more severe sequelae; abortion and neurologic disease. The virus can also undergo latency during which viral genes are minimally expressed, and reactivate to produce lytic infection at any time. Recently, there has been a trend of increasing numbers of outbreaks of a devastating form of EHV-1, equine herpesviral myeloencephalopathy. This review presents detailed information on EHV-1, from the discovery of the virus to latest developments on treatment and control of the diseases it causes. We also provide updates on recent EHV-1 research with particular emphasis on viral biology which enables pathogenesis in the natural host. The information presented herein will be useful in understanding EHV-1 and formulating policies that would help limit the spread of EHV-1 within horse populations. [ABSTRACT FROM AUTHOR]