David Walter Horohov

University of Kentucky | UKY · Department of Veterinary Science

Objective: To perform lipidomic analysis of surfactant and plasma from asthmatic and healthy horses. Animals: 30 horses with clinical signs of asthma and 30 age-matched control horses. Procedures: Detailed history, physical examination, CBC, and bronchoalveolar lavage fluid (BALF) cytologies were obtained. Asthmatic horses were grouped based o...

Studies investigating age-related changes in the function of monocytes are currently limited for horses. Thus, the main goal of this study was to determine the effect of aging on monocyte phagocytic capacity and pro-inflammatory cytokine responses to bacterial lipopolysaccharide (LPS). A second goal of this work was to examine the effect of aging o...

Nocardioform placentitis is characterized by focal, mucoid placentitis resulting in late-term abortion, premature birth, or small, full-term foals, occur sporadically, and are most commonly associated with Crossiella equi and Amycolatopsis spp. infection. The goal of this project was to develop an enzyme-linked immunosorbent assay (ELISA) for quant...

The use of lipopolysaccharide (LPS) to induce a localized source of inflammation (acute synovitis) and allow for monitoring of changes in systemic mRNA expression has been recently reported. Here, the goal was to maintain a significant systemic mRNA response while limiting the severity of lameness such that this model can be used to examine the eff...

Background Immunological mechanisms involved in the pathogenesis of mild to moderate equine asthma (MEA) are not completely understood. There are limited data on bronchoalveolar lavage fluid (BALF) and blood inflammatory cytokine profiles in racehorses with MEA, and the effect of racing on inflammatory cytokines is unknown. Hypothesis/objectives W...

Background: The ability to identify horses at risk for catastrophic injuries continues to be a pressing issue for the racing industry, especially given recent events in North America. Objectives: Since most catastrophic injuries occur in areas of existing pathology and this pathology is likely to elicit an inflammatory response, it was hypothesi...

While the use of lipopolysaccharide (LPS) to induce inflammation has been well described in the horse, the object of this study was to evaluate the effect of repeated intra-articular LPS injections and determine whether this method may be of use to assess changes in gene expression related to inflammation. Six mixed breed horses were utilized for t...

Research in Thoroughbred racehorses has demonstrated continual training leads to a decrease in pro-inflammatory gene expression as horses become race fit, although not all horses experience this predicted decrease. Here, the goal was to determine whether pre-race inflammatory marker mRNA expression correlates with race performance and other horse-s...

Equine herpesvirus type 4 (EHV-4) is mildly pathogenic but is a common cause of respiratory disease in horses worldwide. We previously demonstrated that unlike EHV-1, EHV-4 is not a potent inducer of type-I IFN and does not suppress that IFN response, especially during late infection, when compared to EHV-1 infection in equine endothelial cells (EE...

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 r...

To date, no commercial vaccine label has a claim to be fully protective against the diseases caused by equid herpesvirus 1 (EHV-1), especially the neurologic form. The interferon (IFN) system, of which type I IFN is of great importance, still remains a viable immunotherapeutic option against EHV-1 infection. The type I IFN system has been exploited...

The objectives of this study were to evaluate the natural age-related variation and compare the level of pro-inflammatory cytokines in the peripheral blood and lower airways of horses. The mRNA expression of IL-1β, IL-6, IL-8 TNF-α TLR-4 in bronchoalveolar lavage (BAL) fluid and peripheral blood mononuclear cells (PBMC) were studied by quantitative...

Previous work to evaluate various risk factors for failure to complete competitive endurance rides has examined clinicopathologic parameters, measurements of inflammation, and speed. Here, inflammatory markers were measured before, during, and after a long-distance, competitive endurance ride to examine the intraride dynamics of inflammatory marker...

Equine herpesvirus-1 (EHV-1) infection is an important and highly prevalent disease in equine populations worldwide. Previously we have demonstrated that a neuropathogenic strain of EHV-1, T953, suppresses the host cell's antiviral type-I interferon (IFN) response in vitro. Whether or not this is unique to EHV-1 strains possessing the neuropathogen...

Equine herpesvirus-1 infection is an important disease in the equine industry that causes respiratory disease, sporadic abortion during the third trimester of gestation, birth of weak newborns, and neurological disease syndromes in fatal cases. The recent increase in the incidence, morbidity and mortality associated with the neuropathogenic phenoty...

Since a vaccine is not available against Rhodococcus equi, R equi-specific hyperimmune plasma (HIP) is commonly used, although its efficacy remains controversial. The objective of this study was to evaluate the ability of a commercially available HIP to prevent clinical rhodococcal pneumonia in neonatal foals after experimental challenge. Nine foal...

Since a vaccine is not available against Rhodococcus equi, R equi-specific hyperimmune plasma (HIP) is commonly used, although its efficacy remains controversial. The objective of this study was to evaluate the ability of a commercially available HIP to prevent clinical rhodococcal pneumonia in neonatal foals after experimental challenge.

Given the growing number of older horses worldwide, we are now facing new challenges with the paradox of an old horse population with increased longevity and the potential of increased age-associated diseases. It has been appreciated for many years that the immune system undergoes gradual deterioration with age, referred to as immunosenescence. Whi...

Encysted cyathostomin larvae are ubiquitous in grazing horses. Arrested development occurs in this population and can lead to an accumulation of encysted larvae. Large numbers of tissue larvae place the horse at risk for developing larval cyathostominosis. This disease complex is caused by mass emergence of these larvae and is characterized by a ge...

Rhodococcus equi is a common cause of pneumonia in young foals worldwide and has considerable economic effects on the global equine industry. Despite ongoing efforts, no vaccine is currently available to prevent rhodococaal pneumonia. This is due, in part, to an incomplete understanding of the protective immune response to this bacterium. While ant...

Lentiviral Envelope (Env) antigenic variation and related immune evasion present major hurdles to effective vaccine development. Centralized Env immunogens that minimize the genetic distance between vaccine proteins and circulating viral isolates are an area of increasing study in HIV vaccinology. To date, the efficacy of centralized immunogens has...

In the horse, Lawsonia intracellularis infection results in equine proliferative enteropathy (EPE). While upwards of 100% of weanlings on an endemic farm may seroconvert, only a small percentage (approximately 5%) will develop clinical disease. Cell-mediated immune mechanisms likely play a role in resistance to L. intracellularis and the absence of...

In the absence of an effective vaccine, the success of the test and removal approach for the control of equine infectious anemia (EIA) cannot be overstated, at least in those areas where testing has been traditionally routine. This article addresses 4 main aspects: what has been learned about EIA virus, host control of its replication, and inappare...

The modern horse, Equus caballus has historically made important contributions to the field of immunology, dating back to Emil von Behring's description of curative antibodies in equine serum over a century ago. While the horse continues to play an important role in human serotherapy, the mouse has replaced the horse as the predominant experimental...

Lawsonia intracellularis is the etiologic agent for equine proliferative enteropathy (EPE), which typically affects weanling and yearling horses. In North America, EPE cases often occur between August and January, although cases outside of this time frame have been reported. Clinical signs of EPE are usually nonspecific and include lethargy, pyrexi...

Reasons for performing studyRhodococcus equi is a common cause of foal pneumonia; however its diagnosis remains a challenge for equine veterinarians. While the VapA-specific IgG ELISA has low sensitivity and specificity for detecting pneumonic foals, little is known about VapA-specific IgG subclasses.Objectives To evaluate the performance of VapA-s...

Reasons for performing studyMultiple hypotheses into the age-based susceptibility of animals to Lawsoniaintracellularis exist, including the decline of passively acquired antibodies. Objectives To determine whether the decline in passively acquired antibodies in horses is responsible for the age predilection of equine proliferative enteropathy (EPE...

Rhodococcus equi is the most common cause of pneumonia in young foals. A vaccine is not available and the use of R equi-specific hyperimmune plasma (HIP) is common. Despite its widespread use, the efficacy of HIP in preventing disease remains controversial. The objectives of this study were (1) to evaluate the virulence associate protein A (VapA)-s...

Reasons for performing the studyNeonatal sepsis is a common problem in foals and is a primary cause of death in the post natal period. Transient bacteraemia and subsequent host responses have not been described in the equine neonate. Objectives The primary objective of this study was to determine if transient bacteraemia occurs in foals within the...

Equine proliferative enteropathy (EPE) is an enteric disease of foals that is caused by Lawsonia intracellularis. Clinical cases have been reported worldwide; however, data regarding the epidemiology of L. intracellularis in horses are scarce. Thus far, L. intracellularis has not been reported in the Middle East. The objectives of this study were t...

An imbalance in various cytokine mRNA expression in bronchoalveolar lavage (BAL) and peripheral blood mononuclear cells (PBMC) in horses suffering from recurrent airway obstruction (RAO) has been demonstrated; however, the natural variation of cytokine expression in healthy horses has yet to be described. The objectives of this study were to: 1) id...

Reasons for performing studyAnthelmintic treatments have been associated with local inflammatory reactions. Since each class of anthelmintic has unique mechanisms of action affecting different subpopulations of parasites, we hypothesised that they will also induce characteristic pro-inflammatory responses.Objectives To determine the effect of anthe...

Reasons for performing studyResearch has shown that 6 hours after breeding is a critical time during the uterine innate immune response, and the failure to respond appropriately will result in persistent breeding-induced endometritis (PBIE). This presents a potential opportunity to modulate the course of inflammation towards a timely resolution.Obj...

Objective: To determine the effects of advanced age on whole-body protein synthesis and activation of the mechanistic target of rapamycin (mTOR) signaling pathway in skeletal muscle of horses. Animals: Six 22- to 26-year-old (aged) and six 7- to 14-year-old (mature) horses. Procedures: Whole-body protein synthesis was measured with a 2-hour pr...

Investigation of age-related changes in immune responses in aged horses given equine influenza vaccines

Lentiviral envelope (Env) antigenic variation and associated immune evasion present major obstacles to vaccine development. The concept that Env is a critical determinant for vaccine efficacy is well accepted, however defined correlates of protection associated with Env variation have yet to be determined. We reported an attenuated equine infectiou...

Selenium status has been reported to affect immune function across many different species. Yet few studies have focused on the effect of Se status on the equine immune system. This study examined the effect of Se supplementation on vaccination response and immune function in mature horses. Twenty-eight horses were blocked by age and sex, and random...

The addition of streptolysin-O (SLO) to the standard antibiotics regimen was shown to be superior to antibiotics alone after experimental infection of foals with Rhodoccocus equi (R. equi). The objective of this study is to investigate this response by determining the site-specific expression of extracellular matrix (ECM) and inflammatory response...

Transient endometritis after breeding is necessary for clearance of bacteria and spermatozoa; however, in a subpopulation of mares, the inflammation fails to resolve in a timely fashion. The objective of this study was to describe the uterine inflammatory response in mares susceptible or resistant to persistent breeding-induced endometritis (PBIE)...

The hypotheses that endophyte (Neotyphodium coenophialum) infected fescue seed causes vasoconstriction in horses in vivo, and that ground seed would be cause more pronounced vasoconstriction than whole seed, were tested. Ten horses each received 1 of 3 treatments: endophyte-free ground seed (E-G; n=4 horses), endophyte-positive whole seed (E+W, n=3...

Although the importance of coenzyme Q10 (CoQ10) in health and disease and its critical role in cellular bioenergetics have been well established in various species, there is a total lack of information on the role of CoQ10 in horses. Therefore, the present study was undertaken first to ascertain the occurrence of CoQ10 and/or possibly other homolog...

The weaning process of foals involves a period of considerable stress which likely contributes to an increased risk of infectious disease in these young horses. Mechanisms responsible for this heightened risk of infection remain unknown, although likely due to compromised cell-mediated immunity. Parapoxvirus ovis (PPVO), an immmunomodulator, has be...

Diseases of the lower airways represent some of the most common conditions affecting horses of all ages, but the type and severity tends to follow the horses' age. The age-related dysregulation of pro-inflammatory cytokines may, in part contribute to the development of the diseases. Therefore, we hypothesize that the expression of pro-inflammatory...

The inflammatory response to vigorous exercise ranges from the mild symptoms of delayed-onset muscle soreness to debilitating injuries affecting soft tissue, joint, and bone. Although there is a great deal of information available on the inflammatory response to exercise in human athletes, less information is available regarding the inflammatory re...

While born with a limited production, foals' interferon-gamma (IFN-γ) expression increases after birth. The underlying mechanisms remain unknown. DNA methylation is considered to be involved in. Therefore, the DNA methylation status of the Ifng promoter in CD4(+) cells from neonatal foal was determined using a methylation-specific PCR (MSP), and it...

The effects of selenium (Se) supplementation and source on equine immune function have not been extensively studied. This study examined the effects of oral Se supplementation and Se source on aspects of innate and adaptive immunity in horses. Fifteen horses were assigned to 1 of 3 groups (5 horses/group): control, inorganic Se (sodium selenite), o...

The role of endotoxemia in the development of laminitis remains unclear. Although systemic inflammation is a risk factor for laminitis in hospitalized horses, experimental endotoxin administration fails to induce the disease. While not sufficient to cause laminitis by itself, endotoxemia might predispose laminar tissue to damage from other mediator...

Distinct from human lentivirus infection, equine infectious anemia virus (EIAV)-infected horses will eventually enter an inapparent carrier state in which virus replication is apparently controlled by adaptive immune responses. Although recrudescence of disease can occur after immune suppression, the actual immune correlate associated with protecti...

The effect of organic and inorganic sources of selenium (Se) on measures of Se status of mares and their foals, Se concentrations of colostrum and milk, and indices of immune function of foals was studied. Twenty late-gestation Standardbred mares were randomly assigned to one of two groups. All mares received an identical balanced ration, except fo...

Equine influenza A (H3N8) virus infection is a leading cause of respiratory disease in horses, resulting in widespread morbidity and economic losses. As with influenza in other species, equine influenza strains continuously mutate, often requiring the development of new vaccines. Current inactivated (killed) vaccines, while efficacious, only offer...

The goal of this experiment was to test the hypothesis that quercetin would alter markers of athletic performance as well as markers of exercise-induced inflammation. Six healthy, unfit Standardbred mares (~500 kg, age 4-5 years) were assigned to one of two treatments (quercetin or water) in an experiment conducted in a crossover fashion. The horse...

This study tested the hypothesis that old and young mares exhibit different endocrine responses to a frequently sampled intravenous glucose tolerance test (FSIGT) and different cytokine profiles in blood, adipose and muscle tissues. It was also hypothesised that exercise training alters endocrine and tissue cytokine profiles. Pilot data from 15 mix...

Exercise is known to increase reactive oxygen species and alter glutathione peroxidase activity (GPx), a selenoenzyme responsible for neutralising hydrogen peroxide. This study evaluated the effect of selenium (Se) status on the response of unfit horses to mild exercise. 25 mature horses received one of four dietary treatments for 29 weeks: low Se...

In a recent study, we demonstrated that the virulent Bucyrus strain (VBS) of EAV could infect in vitro a small population of CD3(+) T lymphocytes from some but not all horses. Furthermore, we have shown that a common haplotype is associated with this in vitro CD3(+) T cell susceptibility/resistance phenotype to EAV infection. In this study, we inve...