A 19-year-old Cob mare with atrial fibrillation (AF) presented for transvenous electric cardioversion (TVEC). Under general anaesthesia, three successive incremental electric shocks were given (total 750 Joules) and sinus rhythm was temporarily restored. After 13 seconds, AF recurred so a fourth shock (300 Joules) was given and intravenous (IV) amiodarone started. Shortly after, capnography revealed an acute drop in the end-tidal carbon dioxide, which was followed by agonal gasping. Echocardiography showed severe cardiac dysfunction. Successful cardiac resuscitation consisted, amongst others, of cessation of amiodarone, and administration of dobutamine and adrenaline. This case report highlights the importance of capnography as a non-invasive means of cardiac output monitoring in equine anaesthesia which definitely contributed to a positive outcome. It also emphasises the critical importance of early recognition and communication of complications within anaesthetic and cardiology teams.

Due to the length of the reserve crown and roots of equine cheek teeth, especially in younger horses, their extraction (exodontia) can be a challenging procedure with the potential for many types of post-extraction complications to develop. The prevalence of post-extraction complications is greatly influenced by the exodontia technique used, with unacceptably high levels of complications with the traditional repulsion technique and conversely, low levels of complications with oral extraction performed by skilled operators. Recent objective studies on post-exodontia problems in horses have also highlighted some risk factors for the development of post-extraction problems including exodontia of rostral mandibular teeth in young horses, and exodontia of teeth with apical infections The recent recognition that some non-healing post-extraction equine alveoli suffer from a disorder very similar to dry socket in humans, may help clinicians to recognise, treat and possibly help prevent this disorder.

A document by Callum Haseler. Click on the document to view its contents.

This report describes the evisceration of the jejunum following acute dehiscence of the abdominal wall in an 18 year old gelding which had undergone treatment for suspected sarcoids on the ventral abdomen with a topical caustic/chemotherapy agent 6 weeks previously. The sarcoid lesions appeared to be responding appropriately to the topical therapy until the day of presentation. The jejunum was safely contained in an abdominal bandage and the horse underwent emergency referral before immediate anaesthesia and further assessment. The horse was euthanased at the owners’ request following a guarded prognosis.

Equine primary hyperparathyroidism is rare compared with the condition in human medicine where it is often encountered and represents the most common explanation for hypercalcemia in the outpatient setting. Primary hyperparathyroidism results from a hyperfunctioning parathyroid gland and surgical treatment (parathyroidectomy) is typically curative. Successful surgical removal of a diseased parathyroid gland can be challenging in horses as both normal and hyperfunctioning glands are difficult to localize. Identification of surgical targets using ultrasonography and/or Technetium-99m sestimibi scintigraphy are useful for this purpose in both the human and equine contexts. However, these localization approaches are not aways effective. Moreover, not all patients are candidates for general anesthesia and surgery and the costs associated with diagnostic localization and parathyroidectomy may be prohibitive for some owners. This commentary presents information about primary hyperparathyroidism in the event that it is not treated and strives to review aspects of the disease when left untreated from the human medical context.

Urethral diverticula have been described in other species. Congenital anomalies of the urinary tract in horses are rare. A 26-year-old gelding presented with complaints of abdominal discomfort and dysuria. Urine dribbling was reported since several years. General clinical examination was within normal limits. Rectal palpation showed a distended bladder, which was emptied spontaneously after manipulation. Urine cytology showed an increased white blood cell count and presence of bacteria. Bacterial culture however remained sterile. Cystoscopy identified two symmetrical urethral diverticula dorsal to the entrance of the bladder, lined with normal epithelium. Mucosa of the bladder, urethra and two diverticula were hyperemic with evidence of urine accumulation in both diverticula. Ultrasound, abdominal and transrectal, did not identify the diverticula. Treatment included trimethoprim-sulfamides and meloxicam. After 2 weeks, the owner reported resolution of clinical signs. It is unclear if the diverticula in this case were congenital or acquired. In humans it is described that urethral diverticula can be asymptomatic and incidental findings. Surgical intervention has been described in small animal and human medicine with complete resolution of clinical signs, however in this case was not possible due to financial restraints.

Septicemia can be a tragic illness in neonatal and young foals. Sick foals may manifest a variety of clinical symptoms all related to a common infection and its systemic effects. While the pathogenesis of this disease is the same as for adult equids, the clinical signs seen can be very different. The rapid changes seen in foal are reflective of their low endogenous reserves of glucose and innate immune mediators as well as the poor ability to self-regulate their metabolism. The neonatal immune system is reliant on maternal antibodies at birth and development of the foal's own system takes a significant amount of time. This non-competent immune system changes how the foal responds to infection when compared to the adult. Clinical signs in septic foals include tachycardia, tachypnea, depression, anorexia, colitis, and fever. Less commonly, foals may show petechiation, swollen joints, anterior uveitis, and coma. This article is the first of a two part series on neonatal sepsis and will present a review on the neonatal immune system, the pathophysiology of sepsis, and the range of clinical signs seen in foals.

Amidst discourse surrounding the racing industry’s social license to operate, the welfare of racehorses and jockeys is often at the forefront of discussions. Specifically, catastrophic events and the sudden death (SD) of horses on race days tend to capture media attention and often place the racing industry under public scrutiny. While such occurrences are not frequent, they have negative ramifications on the welfare of both racehorses and jockeys. The development of advanced diagnostic technology is therefore paramount to bettering the safety and welfare of horses and jockeys, as well as maintaining the integrity of the racing industry. Most importantly, the application of such technology could reduce the prevalence of avoidable injuries and SD. This review discusses the relevance of monitoring horses’ cardiovascular, respiratory, and thermometry biometrics and examines the currently available commercial devices capable of doing so. The review also explores the relevance and application of such devices within the racing industry and suggests how they may fit in with currently-available tools for monitoring the musculoskeletal health of racehorses.

Equine septic fungal arthritis is poorly documented in the literature. There is absence of efficacy and safety data for anti-fungal medications, highlighting the importance of documenting this case. A 15-year-old Irish sport horse gelding presented moderately lame at the walk on the left hindlimb 13 days after intra-articular medication of the left tarso-crural joint with triamcinolone and hyaluronic acid. Radiography revealed an osteochondral fragment at the distal intermediate ridge of the tibia and shallow subchondral bone defect on the medial trochlear ridge. Synoviocentesis yielded a turbid sample with an elevated total nucleated cell count (49x109cells/L; total neutrophil count of 62.8%). Arthroscopic lavage of the tarsocrural joint (TCJ) was performed. Ceftriaxone was administered and systemic antimicrobials initiated. The fungus Wickerhamomyces anomalus was identified on culture. The horse was subsequently intensively treated with antimicrobial and anti-fungal medications, both systemically and intra-articularly over the following 60 plus days. Multiple subsequent synovial cultures revealed the persistence of the fungal organism, until a negative culture on day 55. However, on day 113, a non-weight bearing lameness at trot was present, and a further positive synovial fungal culture. Radiographs revealed a lytic lesion at the distal tibia with marked progression. The horse was euthanised on day 126.

A two-day-old female Warmblood foal (70 kg) presented with a closed, displaced Salter-Harris type-II fracture of the proximal physis of the left hind first phalanx. For fracture repair four 4.5 mm cortical screws and wire in a figure-of-8 pattern were applied on the lateral and medial aspect of the phalanx, respectively. A 4.5 mm cortical screw was additionally inserted in lag-fashion to engage the lateral metaphyseal spike. Three days postoperatively, medial axis deviation and implant infection were noted and revision surgery was performed. Previous implants were removed and two 4.5 mm transphyseal cortical lag-screws were placed in proximolateral-distomedial and dorsoproximal-plantarodistal direction. Postoperatively, the fracture healed rapidly and the implants were removed 6 weeks later. Nineteen months after implant removal the horse did not show any sign of lameness, despite a shortening of the proximal phalanx compared to the contralateral limb. In cases of postoperative implant instability and infection, implant removal often becomes necessary. However, new implants cannot be placed safely in the previous location. To avoid this problem, this report describes an alternative approach for screw positioning in case of previous implant infection in a Salter-Harris type-II fracture of the proximal physis of the first phalanx.

Streptococcus equi subspecies equi (S. equi) is the causative organism of the upper respiratory disease of equids, strangles, characterised by pyrexia, lymphadenopathy, and mucopurulent nasal discharge. Strangles was first reported over 750 years ago and continues to be of significance in equine populations across the globe. This review discusses how S. equi has adapted, the clinical manifestation of strangles, and how clinicians and caregivers can tackle the disease in the future. S. equi evolved from the commensal, and occasionally opportunistic pathogen, Streptococcus equi subspecies zooepidemicus refining its capabilities as it became host restricted. The success of S. equi can be attributed to its ability to cause both acute and persistent infection, the latter occurring in about 10% of those infected. In this carrier state, S. equi persists in the guttural pouch without causing clinical signs, intermittently shedding into the environment, and encountering naïve animals. Insight into the S. equi genome and lifestyle has led to advances in diagnostic assays and the development of a safe and efficacious recombinant-fusion vaccine, giving clinicians and caregivers the tools to better combat this infection. Alongside rigorous biosecurity protocols and pragmatic control measures such as screening new arrivals for exposure and carrier status, these new technologies demonstrate that strangles can be an increasingly preventable infection.

Treatment of guttural pouch mycosis with salpingopharyngostomyAmanda R Watkins1 and Eric J Parente11University of Pennsylvania New Bolton Center, Kennett Square PAThe case report by Rowe et al (2023) published in this issue describes a case of bilateral guttural pouch mycosis in a 9-month-old thoroughbred colt that was diagnosed due to unusual severe neurologic abnormalities including neck pain and abnormal head carriage. There was no evidence of hemorrhage in this case and therefore the colt was treated with debridement of the mycotic plaques, topical enilconazole, and ultimately a salpingopharyngeal fistula in the dorsal pharyngeal recess to inhibit the growth of the mycosis. The treatments were successful, and the colt went on to race.The guttural pouch is an diverticulum of the auditory tube that is found in ungulates possessing an odd number of toes, including the horse.1 The guttural pouches are susceptible to fungal and bacterial infections and the intimate association of the pouches with major arteries and nerves makes such infections potentially life-threatening. While the purpose of the guttural pouch is an area of speculation among equine researchers it is thought that cooling the blood before it reaches the brain especially during exercise is an important function.1 The cooling of the blood is achieved by a large air filled space separated from the internal carotid artery by only a thin membrane. Therefore, any locally invasive disease within the guttural pouches can have dire consequences.Fungal infection of the guttural pouch occurs rarely but, due to its anatomical position in relation to many neurovascular structures of the head, even mild disease can result in fatal hemorrhage and neurological sequelae.2 Obtaining a positive culture from these cases can be difficult however the most commonly isolated fungal species is Aspergillus fumigatus.2 The warm, dark, and humid environment of the guttural pouch may predispose it as a site of fungal infection. Jukic et al showed that the oxygen and carbon dioxide partial pressures within the guttural pouch vary significantly between horses and that they remain relatively static throughout the respiratory cycle in a normal guttural pouch.3 This inter-horse variation may explain the seemingly random distribution of horses that are affected by guttural pouch mycosis. Additionally the individual differences may contribute to the less aggressive phenotype that resolves without treatment in 15-28 days that is seen in the experimentally induced Aspergillus guttural pouch mycosis model.4 The case described in this report may have been complicated by the mixed infection cultured from the guttural pouch of both Aspergillus fumigatus and Streptococcus equi subsp. zooepidemicus .Salpingopharyngostomy is the creation of a fistula between the pharynx and the guttural pouch and has been described as a treatment for guttural pouch mycosis.3,5–7 The theory behind this procedure is that it opens the guttural pouch to the fluctuating change of respiratory gases and temperatures of the respiratory tract. Jukicet al demonstrated that following salpingopharyngostomy there was no difference in the mean partial pressures of oxygen and carbon dioxide within the guttural pouch however, the variability of the pressures was significantly increased with the partial pressures oscillating with the respiratory pattern.3 This introduction of varying gas levels may change the environment within the guttural pouches making them less hospitable to fungal growth and allowing for faster resolution of the infection. In this case, due to the bilateral nature of the disease the authors created a single salpingopharyngostomy in the dorsal pharyngeal recess to gain access to both guttural pouches simultaneously. Creating a bilateral opening is easily created and can even be made larger and more likely to remain patent by ablating part of the septum between the two pouches.Aspergillus species are highly aerobic and can grow in most oxygen environments. However, they are also capable of growing at low oxygen tension and growth under these conditions may affect their pathogenicity by allowing secretion of virulence factors.8Hyperbaric oxygen treatment of A. fumigatus biofilms in vitro resulted in decreased biofilm proliferation by over 50%, though the effect was transient with growth re-establishing at 6 hours post treatment.9 In human medicine, individuals with invasive fungal infections caused by Aspergillus spp . are routinely treated with hyperbaric oxygen therapy in addition to surgical debridement and anti-fungal medications.10 Though there is a lack of controlled evidence to support this therapeutic in fungal infection, the complications are minimal and it is thought to improve the efficacy of neutrophils and macrophages by meeting their increased oxygen demands when clearing infections.11Additionally increased oxygen may improve the quality of the collagen matrix being created during the healing process.11An additional therapeutic that might have been helpful in this case prior to salpingopharyngeal fistulation is topical oxygen therapy (TOT) which has been recently published by Lepage et al for use as an adjunct treatment in epistaxis cases following transarterial coil embolization (TACE) or as a primary treatment in non-bleeding cases.12 Part of the rationale behind pursuing additional treatment options by this group is the percentage of horses that fail to completely resolve the neurologic sequelae of the disease which has been reported at 50%.13 When examining the issue of recurrent epistaxis following TACE the survival rate is 84% which places this high level of persistent neurological abnormalities into sharp relief. Dysphagia particularly can be severe enough to necessitate euthanasia even in the face of successful hemorrhage management. Certainly, dysphagia can be reversible as in the case published by Whitehead et al that was managed successfully with topical anti-fungals, carotid occlusion and esophagostomy but it can be a lengthy process that not all owners or patients will tolerate.14Guttural pouch mycosis does not lend itself to aggressive surgical debridement given the closely associated vessels and nerves to the mycotic plaques, however the somewhat enclosed environment of the guttural pouch may be an advantage for TOT. Lepage et al treated cases with TOT 4 times per day at 15 L/min for 1-2 weeks by placing an indwelling catheter into the affected guttural pouch and leaving it in place as much as possible for the duration of hospitalization. During treatments the horses were restrained with their heads at the height of the withers to decrease the opening of the guttural pouch orifice to maintain a closed high oxygen environment, though swallowing would still result in transient openings of the orifices.12Following a minimum of two treatments the fungal plaques were seen to begin regressing. Additionally the reported resolution or significant improvement of 10/12 neurologic disorders is encouraging compared to the 9/18 cases of resolution reported in a larger retrospective study on TACE.13It is unlikely TOT and salpingopharyngostomy would have any additive effect if done concurrently since it is unlikely the higher oxygen tension could be achieved with the fistula. The two procedures could be considered in series with the salpingopharyngostomy created after initial TOT. The advantage of the salpingopharyngostomy alone is that it is a single treatment without the need for further treatments or hospitalization. Furthermore, while Jukic et al showed some variations in partial pressures of gas in horses with salpingopharyngostomies there was not significant variation in temperature or humidity. The horses were housed in a controlled environment during short sampling periods in that study and variations may be greater if horses with salpingopharyngostomies are not housed in an environmentally controlled condition.Some of the clinical signs of this case report are difficult to attribute directly to the mycosis infection and there was confounding evidence of bacterial infection and other treatments. Regardless, guttural pouch mycosis can result in severe and possibly fatal disease as it almost did in this case report. Salpingopharyngostomy is an alternative treatment strategy to traditional medical treatment that should be considered in horses with guttural pouch mycosis.References1. Baptiste KE, Naylor JM, Bailey J, Barber EM, Post K, Thornhill J. A function for guttural pouches in the horse. Nature . 2000;403:382-383.2. Ludwig A, Gatineau S, Reynaud MC, Cadoré JL, Bourdoiseau G. Fungal isolation and identification in 21 cases of guttural pouch mycosis in horses (1998–2002). Vet J . 2005;169(3):457-461. doi:10.1016/j.tvjl.2004.06.0053. Jukic CC, Cowling NR, Perkins NR, Eps AW, Ahern BJ. Evaluation of the effect of laser salpingopharyngostomy on the guttural pouch environment in horses. Equine Vet J . 2020;52(5):752-759. doi:10.1111/evj.132214. Greppi MC, Guillot J, Melloul E, Bourdoiseau G, Lepage O, Cadoré JL. Experimental induction of mycotic plaques in the guttural pouches of horses. Med Mycol . Published online October 4, 2016:myw073. doi:10.1093/mmy/myw0735. Koch DW, Ericksen KA, Easley JT, Hackett ES. Clinical outcome of horses with guttural pouch infection following transpharyngeal fenestration. J Am Vet Med Assoc . Published online May 5, 2022:1-5. doi:10.2460/javma.22.01.00416. Koch DW, Easley JT, Nelson BB, Delcambre JJ, McCready EG, Hackett ES. Comparison of two techniques for transpharyngeal endoscopic auditory tube diverticulotomy in the horse. J Vet Sci . 2018;19(6):835. doi:10.4142/jvs.2018.19.6.8357. Watkins AR, Parente EJ. Salpingopharyngeal fistula as a treatment for guttural pouch mycosis in seven horses. Equine Vet J . 2018;50(6):781-786. doi:10.1111/evj.128308. Hall LA, Denning DW. Oxygen requirements of Aspergillus species.J Med Microbiol . 1994;41(5):311-315. doi:10.1099/00222615-41-5-3119. Dhingra S, Buckey JC, Cramer RA. Hyperbaric Oxygen Reduces Aspergillus fumigatus Proliferation In Vitro and InfluencesIn Vivo Disease Outcomes. Antimicrob Agents Chemother . 2018;62(3):e01953-17. doi:10.1128/AAC.01953-1710. Segal E. Hyperbaric Oxygen in the Treatment of Invasive Fungal Infections: A Single-Center Experience. 2007;9.11. Kaufman H, Gurevich M, Tamir E, Keren E, Alexander L, Hayes P. Topical oxygen therapy stimulates healing in difficult, chronic wounds: a tertiary centre experience. J Wound Care . 2018;27(7):426-433. doi:10.12968/jowc.2018.27.7.42612. Lepage OM, Di Francesco P, Moulin N, et al. The Effect of Topical Oxygen Therapy in Horses Affected with Mycosis of the Guttural Pouch: An Experimental Pilot Study and a Case Series. Anim Open Access J MDPI . 2021;11(11):3329. doi:10.3390/ani1111332913. Lepage OM, Piccot-Crézollet C. Transarterial coil embolisation in 31 horses (1999-2002) with guttural pouch mycosis: a 2-year follow-up.Equine Vet J . 2010;37(5):430-434. doi:10.2746/04251640577447996014.Whitehead AE, Whitty J, Scott M, Léguillette R. Reversible dysphagia secondary to guttural pouch mycosis in a gelding treated medically with voriconazole and surgically with carotid occlusion and esophagostomy.Can Vet J . 2018;59(2):165-170.

Bladder prolapse is a rare condition in mares and may occur as a result of excessive straining during the parturition or in the postpartum period. We report a case of dystocia associated prolapse and incarceration of the small colon through the external urethral opening into a prolapsed urinary bladder. No previous reports of this condition were found. An 11-year-old Thoroughbred mare was presented to The Equine Hospital at the Jockey Club of Saudi Arabia for evaluation and treatment of dystocia. Prolapse of the urinary bladder was concomitantly diagnosed. Initial assessment deemed replacement of the urinary bladder in the normal position and vaginal delivery not possible. The mare was immediately prepared for caesarean section. The foal was successfully delivered and resuscitated. Detailed assessment of the bladder during the surgery revealed that the small colon had prolapsed through the external urethral opening and was inside the bladder. The urinary bladder was opened. The small colon was replaced into the abdominal cavity; a first surgeon gently replaced the small colon through the external urethral sphincter and a second surgeon retrieved the small colon by gentle traction. The mare recovered uneventfully from general anaesthesia. The mare and the foal were discharged from the hospital seventeen days post-operatively.

The case report by Navarro-Lopez et al., (2023) in this issue describes a thorough differential diagnosis in an equine with acute neurological disease. Rabies was confirmed by direct fluorescent antibody test (DFA). Rabies virus (RABV) was isolated from brain tissue of the ill mare by intracerebral inoculation in sucking mice. Sequencing and phylogenetic inference allowed the identification of the rabies virus variant (RVV) associated with this case. Thus, Navarro-Lopez et al., reported that the rabid mare got infected with a rabies virus variant associated with skunks. This clinical commentary elaborates on the seemingly rare skunk rabies across North America (NA) highlighting its relevance in human and animal health that have remained somehow neglected

Background: A reduction in the Egg Reappearance Period (ERP) has been suggested to be an early indication of emerging anthelmintic resistance in strongyles. Objective:To measure the strongyle ERP following moxidectin treatment of horses in the southeast of England. Study Design: Prospective study. Methods: Horses with a faecal egg count (FEC) of > 400 strongyle eggs per gram (EPG) in a routine screening sample were enrolled into the study. Moxidectin (400 mcg/kg) was administered per os and FEC tests repeated every 2 weeks for 16 weeks. Results: Forty-eight horses completed the study. The mean EPG prior to treatment was 1047 (range 375 – 2137 EPG). In all but two horses, FEC was 0 EPG 2 weeks after moxidectin administration. In the remaining two, the FECs were 12.5 EPG (97.8-98.3% reductions compared to pre-treatment FEC). At 4 weeks post-treatment, 6 horses had positive FECs (96.6-99.2% reductions). At 6 weeks, 11 horses had positive FECs (83.8% reduction in one horse; >90% reduction in 10). At 8 weeks, 21 horses exhibited positive FECs (<90% reduction in 2). At 10 weeks, 27 horses had positive FECs (<90% in 6). At 12 weeks, 31 horses had positive FECs (<90% reduction in 11). At 14 weeks, 34 horses had positive FECs (<90% reduction in 13). At 16 weeks, 38 horses had positive FECs (<90% reduction in 17). Limitations: Weights of some horses were estimated using weigh tapes rather than a weighbridge. Dosing of the horses with moxidectin was carried out by owners. Conclusions: The results indicated acceptable efficacy of moxidectin at 14 days after treatment; however, the ERP pattern measured across the group suggest that this anthelmintic has a considerably shorter suppressive effect on strongyle egg shedding than measured when it was first introduced ( >13 weeks and up to 24 weeks).

Thoracic hemivertebra is one of the rare congenital vertebral anomalies in horses resulting in vertebral column deformity with or without neurological signs. A nine-month-old Racking filly was presented with a distinct bump over the back region. This bump was apparent at birth and has been increasing in size. Clinical examination revealed a painless kyphoscoliosis over the thoracic vertebrae with mild ataxia and abnormal gait of hindlimbs. In plain lateral radiographs of thoracic vertebrae, hemivertebrae were seen in the 13th-15th thoracic vertebrae. At myelography performed under general anaesthesia, the ventral and dorsal aspects of the contrast medium column were narrowing at the level of the 13th-14th thoracic vertebrae, and no sign of contrast medium after the 14th thoracic vertebra that represents spinal cord compression. Little information about hemivertebra in horses exists and a better understanding of hemivertebra etiology is required.

Background: Analgesic protocols related to orchiectomy or castration of young horses vary widely depending on geographic location, educational background of the veterinarian, and other demographic factors. Specific practices of equine veterinarians in the United States (US) have not been reported. Objectives: To determine perioperative pain management practices of equine veterinarians in the US as they relate to castration of young male horses. Study Design: Cross-sectional survey Methods: An internet-based questionnaire included items related to analgesic drugs used in association with castration of healthy yearling colts. Demographic and educational factors associated with routine recommendation of analgesic medications after castration were analyzed using logistic regression. Results: Responses from 146 equine veterinarians in the US revealed that 112/146 (76.7%) administered a nonsteroidal anti-inflammatory drug (NSAID) at the time of castration. Routine recommendation of post-castration analgesia was associated with veterinarians who were employed in a multi-veterinarian practice, completed their veterinary education after 2000, and provided a higher pain severity score for horses at 24 hours after a routine castration. Main Limitations: Possible distribution, self-selection, response, and recall biases as a result of convenience sampling methodology. Conclusions: Perioperative pain management practices vary widely among US veterinarians but the majority of veterinarians, especially more recent graduates, recommend administration of an NSAID.

Background: Neonatal foals are born essentially agammaglobulinemic and therefore must ingest colostrum or receive immunoglobulins to maintain health. Failure of passive transfer treatment involves administration of equine colostrum, plasma or commercial powdered colostrum (CPC). Anecdotal reports suggest a risk of anaphylaxis associated with plasma transfusion in neonates that received CPC prior to gut closure. Bovine serum albumin (BSA) in CPC may serve as a target for BSA-specific immunoglobulin E (IgE) in donor equine plasma. Objectives: To determine presence of BSA-specific IgE in samples collected post-routine vaccination in healthy horses, horses experiencing adverse vaccine reactions and commercial equine plasma. Study Design: Prospective Observational Methods: Serum was collected from 65 healthy horses at day 0, 14, 28, 90, 180, 270 and 365 post-vaccination, 26 horses after vaccine reaction at day 1, 180 or 270 post-vaccination, 4 horses not vaccinated and 10 horses from a commercial plasma donor herd. BSA-specific IgE was determined using enzyme-linked immunosorbent assay (ELISA). Results: BSA-specific IgE was not detected in non-vaccinated horses and was identified in all vaccinated horses. Younger horses demonstrated higher fold changes in post-vaccination BSA-specific IgE expression compared to older horses. No significant difference in BSA-specific IgE levels between commercial plasma donors and healthy horses was identified. No significant difference in post-vaccination anti-BSA IgE levels between reactor and healthy horses at day 180 and 270 post-vaccination were identified. Main Limitations: Small number of reactor horses at day 180 and 270 post-vaccination with most samples being collected 24 hours. There were no healthy horse samples for 24 hours post-vaccination; therefore, it was not possible to compare the two groups at this timepoint. Conclusions: Horses may express BSA specific IgE following vaccination. There may be risk of hypersensitivity type reaction when veterinarians administer commercial plasma to neonatal foals that have consumed CPC prior to gut closure.