Highlights of recent clinically relevant papers

This study by Amie Kapusniak and co-workers in Australia aimed to determine the heritability of sudden cardiac death in a sample population of Thoroughbred racehorses. Horses with sudden cardiac death were identified from steward and post-mortem reports of Thoroughbred racehorses in Australia (2007–2020). Control horses were randomly selected from races in which sudden cardiac death occurred or from races on the date of the case fatality. A five-generation integrated pedigree chart was collected for each horse. Estimates of heritability were obtained using an animal model in the ASReml-R program with variance components estimated assuming sudden cardiac death was normally distributed, and on the logit transformed scale. Inbreeding coefficients were calculated and the risk of producing sudden cardiac death-affected progeny was calculated for stallions that sired ≥5 individuals in the case–control population. Ninety-three horses with sudden cardiac death and 465 control horses were identified. Heritability on the underlying scale was 0.15 ± 0.09 (logit animal) and 0.24 ± 0.12 (normal animal). Inbreeding coefficients were not significantly different between groups. Of the 16 first generation sires that appeared ≥5 times in the case–control data set, two sires more frequently produced affected progeny (OR 7.95–10.41). These results show that heritability of sudden cardiac death in this population was relatively low. However, individual stallions appear more likely to produce affected progeny. In this study M.G. Myhre and co-workers in the United States investigated anaesthesia-related morbidity associated with recumbent, low-field magnetic resonance imaging (MRI) of horses. Medical records from a private equine referral hospital were analysed for cases that underwent general anaesthesia for low-field MRI of the distal limb. These were used to determine peri-anaesthetic morbidity and mortality. A total of 243 anaesthetic episodes were recorded in horses undergoing low-field MRI. The peri-anaesthetic complication rate prior to discharge was 6.2% (15/243). No patients experienced a fatal complication. Multiple sites were imaged in 92 of the 243 patients, 90/243 received pre-anaesthetic dantrolene, 134/243 received intra-anaesthetic dobutamine, and 15/243 were positioned in dorsal recumbency. Complications included abdominal discomfort (colic; 9/243), myopathy (4/243), hyphaema (1/243) and carpal fracture (1/243). At the time of discharge, 14/15 complications had resolved. Of 135 horses for which data were available 55 became hypotensive during the procedure (lowest mean arterial pressure <65 mmHg). Median body weight was 553 (min 363, max 771) kg. Horses were anaesthetised for a median of 150 (min 45, max 210) minutes. There was no evidence of an association between higher body weight or longer duration of anaesthesia and development of an anaesthetic complication. For categorical variables (dantrolene administration pre-anaesthesia, dobutamine administration during anaesthesia, hypotension (mean <65 mmHg) during anaesthesia, dorsal versus lateral recumbency and imaging of single vs multiple sites), the 95% CI for the OR included 1, indicating a lack of effect of the variable on the odds of complication. These results suggest that low-field MRI under general anaesthesia is a viable option for diagnostic imaging in otherwise healthy horses. Complications occur, but most resolve before discharge. This desk-based ethico-legal study by Madeleine Campbell and Benjamin Sykes applied Campbell's Ethical Framework for the Use of Horses in Sport to the question: ‘Should the use of omeprazole be allowed during equestrian competition?’ Campbell's Ethical Framework for the Use of Horses in Sport was applied in a stepwise fashion: definition of the ethical question; analysis of the evidence base; consideration of stakeholders' interests; harm:benefit analysis; application of the three central tenets of the framework, and formulation of conclusions and recommendations. Stakeholders in equine sports have a variety of (frequently conflicting) interests; all of them share an interest in optimising equine welfare. The incidence of equine gastric ulcer syndrome (EGUS) in competition horses is high. Omeprazole is a cornerstone treatment. There are currently discrepancies in regulation about the use of omeprazole during competitions. Recent evidence suggests that withholding omeprazole treatment for two clear days before competition allows the recurrence of squamous EGUS, whereas withholding treatment on the day of competition only does not have that effect. Based on recent scientific evidence, if horses are being treated with omeprazole outside of competition, then treatment on the day of competition should be permitted on welfare grounds. Revision of regulations around the use of omeprazole during competition by governing bodies is necessary to safeguard the ethical use of horses in sport. This study by Amanda Craven and co-workers in the United States and the Netherlands described the clinical findings and outcome predictors for multinodular pulmonary fibrosis (EMPF) in 46 horses. Radiographic (n = 27) and ultrasonographic studies (n = 19) from EMPF horses and bronchoalveolar lavage fluid (BALF) cytology from 6 EMPF and 13 asthma cases were independently reviewed and blinded to diagnosis and outcome. Associations between predictor variables and survival were assessed by predictor screening followed by Fisher's exact and Wilcoxon rank sum tests. Primary clinical findings were weight loss (36/46, 78%), increased respiratory effort (33/46, 72%), tachypnoea (32/46, 70%) and fever (18/46, 39%). Macrophage atypia was seen in more EMPF than asthmatic horse BALF (67% vs. 8%). Equine herpesvirus 5 (EHV-5) was detected in 24 of 30 (80%) and hyperfibrinogenaemia in 25 of 28 (89%) cases. Twenty-seven of 46 horses (59%) and 11 of 45 (24%) survived to discharge and to 3 months, respectively. Three-month survival was associated with lower median (range) respiratory rates (30 [24–36] vs. 41 [30–60] breaths/min), and higher BALF lymphocyte: neutrophil ratios (4.7 [1.4–22] vs. 0.47 [0.11–1.9]) and blood lymphocyte counts (1.25 [0.93–2.55] vs. 0.90 [0.70–1.24] × 109/L). Imaging findings, EHV-5 detection, and corticosteroid treatment were not associated with survival. Fever is not a sensitive clinical sign of EMPF. Diagnostic testing should be pursued for horses with increased respiratory rate and effort and weight loss. The prognosis for EMPF horses is poor. Corticosteroid treatment does not improve 3-month survival. This study by Alexis Powers and co-workers in the United States aimed to evaluate the clinical phenotype, blood vitamin E concentrations before and after supplementation and pedigree in a cohort of Gypsy Vanner (GV) horses with a high prevalence of neurologic disease suspicious for equine neuroaxonal dystrophy/degenerative myeloencephalopathy (eNAD/EDM) and also to confirm eNAD/EDM in GVs through post-mortem evaluation. Neurologic examination was performed on all 26 GVs in this study, which were from one farm in California and two cases from the Midwestern US. Pre-supplementation blood vitamin E concentration was assessed in 17 GVs. Twenty-three were supplemented orally with 10 IU/kg of liquid RRR-alpha-tocopherol once daily for 28 days. Vitamin E concentration was measured in 23 GVs after supplementation, of which 15 (65%) had pre-supplementation measurements. Two clinically affected GVs from California and the two Midwestern cases had necropsy confirmation of eNAD/EDM. Pre-supplementation blood vitamin E concentration was ≤2.0 μg/mL in 16/17 (94%) of GVs from California. Post-supplementation concentration varied, with a median of 3.39 μg/mL (range, 1.23–13.87 μg/mL), but only 12/23 (52%) were normal (≥3.0 μg/mL). Normalisation of vitamin E was significantly associated with increasing age. Euthanised horses (n = 4) had eNAD/EDM confirmed at necropsy. The authors concluded that GVs could have a genetic predisposition to eNAD/EDM. Vitamin E supplementation should be considered and monitored in young GVs.