Spatial patterns of prostate-specific antigen testing in asymptomatic men across Australia: a population-based cohort study, 2017-2018.

OBJECTIVES: In Australia, while prostate-specific antigen (PSA) testing rates vary by broad area-based categories of remoteness and socio-economic status, little is known about the extent of variation within them. This study aims to describe the small-area variation in PSA testing across Australia. STUDY DESIGN: This was a retrospective population-based cohort study. METHODS: We received data for PSA testing from the Australian Medicare Benefits Schedule. The cohort included men (n = 925,079) aged 50-79 years who had at least one PSA test during 2017-2018. A probability-based concordance was applied across multiple iterations (n = 50) to map each postcode to small areas (Statistical Areas 2; n = 2,129). For each iteration, a Bayesian spatial Leroux model was used to generate smoothed indirectly standardized incidence ratios across each small area, with estimates combined using model averaging. RESULTS: About a quarter (26%) of the male population aged 50-79 years had a PSA test during 2017-2018. Testing rates among small areas varied 20-fold. Rates were higher (exceedance probability>0.8) compared with the Australian average in the majority of small areas in southern Victoria and South Australia, south-west Queensland, and some coastal regions of Western Australia but lower (exceedance probability<0.2) in Tasmania and Northern Territory. CONCLUSIONS: The substantial geographical variation in PSA testing rates across small areas of Australia may be influenced by differences in access to and guidance provided by clinicians and attitudes and preferences of men. Greater understanding of PSA testing patterns by subregions and how these patterns relate to health outcomes could inform evidence-based approaches to identifying and managing prostate cancer risk.

Main COVID-19 information sources in a culturally and linguistically diverse community in Sydney, Australia: A cross-sectional survey.

OBJECTIVE: Describe COVID-19 information-seeking experiences for culturally and linguistically diverse groups in Sydney, Australia. METHODS: Cross-sectional survey, translated into 11 languages; participants recruited from March 21 to July 9, 2021. Regression models identified factors associated with difficulty finding easy-to-understand COVID-19 information. RESULTS: Across 708 participants (88% born overseas, 31% poor English proficiency), difficulty finding easy-to-understand COVID-19 information was rated 4.13 for English (95%CI: 3.85-4.41) and 4.36 for non-English language materials (95%CI: 4.07-4.66) (1 easy to 10 hard). Participants who were older (p < 0.001), had inadequate health literacy (p < 0.001), or poor English proficiency (p < 0.001) found it harder to find easy-to-understand English-language COVID-19 information. Those who had greater difficulty finding easy-to-understand non-English COVID-19 information were younger (p = 0.004), had poor English proficiency (p < 0.001), were university-educated (p = 0.05), and had spent longer living in Australia (p = 0.001). They were more likely to rely on friends and family for COVID-19 information (p = 0.02). There was significant variation in information-seeking experiences across language groups (p's < 0.001). CONCLUSIONS: Easy-to-understand and accessible COVID-19 information is needed to meet the needs of people in culturally and linguistically diverse communities. PRACTICE IMPLICATIONS: COVID-19 communication efforts must involve working alongside these communities to leverage existing communication channels and tailor messages.

An investigation of anthelmintic efficacy against strongyles on equine yards in Scotland.

REASONS FOR PERFORMING STUDY: Cyathostomins comprise 50 helminth species, considered the most problematic equine endoparasites. Three classes of anthelmintic are currently licensed for their control, namely the benzimidazoles (fenbendazole), tetrahydropyrimidines (pyrantel) and macrocyclic lactones (ivermectin and moxidectin). Anthelmintic resistance in cyathostomins is common. With no new classes expected in the near future, it is essential to determine the efficacy of the available anthelmintics to inform future control programmes. OBJECTIVES: To determine the efficacy of all 3 anthelmintic classes against strongyles in equids on livery yards in east and central Scotland. STUDY DESIGN: Anthelmintic efficacy testing using the faecal egg count reduction test (FECRT). METHODS: FECRTs were performed on equids with initial strongyle faecal egg counts (FECs) of ≥50 eggs per gram. Efficacy was determined by comparing pretreatment (Day 0) and 14 days post treatment (Day 14) FECs. The following chemicals were tested: fenbendazole, pyrantel, ivermectin and moxidectin. Group arithmetic mean FECR of >90% for fenbendazole and pyrantel, and >95% for ivermectin and moxidectin, represented efficacy, whereas lower mean FECR indicated potential resistance. RESULTS: A total of 447 FECRTs were performed on 15 yards, as follows (the numbers in parentheses represent the number of yards each anthelmintic was tested on): 55 equids (7 yards) fenbendazole, 111 (8 yards) pyrantel, 163 (13 yards) ivermectin and 118 (10 yards) moxidectin. Fenbendazole resistance was documented on all yards (range of mean FECR, 15.8-83.4%), whereas pyrantel (90.4-99.6%), ivermectin (99.5-100%) and moxidectin (99.4-100%) treatment had acceptable efficacy. CONCLUSIONS: Reduced efficacy of fenbendazole was widespread, whereas >90% efficacy was found after pyrantel, and >95% efficacy after ivermectin and moxidectin. Overall, efficacies were higher than reported previously in Europe and the USA, potentially reflecting differences in management and anthelmintic use on the yards surveyed. POTENTIAL RELEVANCE: The use of fenbendazole for strongyle control in Scotland should be questioned. Targeted use of pyrantel should be encouraged to reduce reliance on macrocyclic lactones. Further work to correlate management practices with the presence of anthelmintic resistance is warranted.

A questionnaire study of equine gastrointestinal parasite control in Scotland.

REASONS FOR PERFORMING STUDY: Anthelmintic resistance in equine gastrointestinal nematodes is a threat to equine health and welfare. Detailed knowledge of anthelmintic use and parasite control methods is a prerequisite to identification of potential risk factors for resistance. OBJECTIVES: To identify parasite control practices employed by equine owners in Scotland and investigate management factors associated with anthelmintic resistance. STUDY DESIGN: Questionnaire study of equine parasite control in Scotland. METHODS: Questionnaires were available electronically, distributed at a conference and mailed to clients. Key areas explored included general background, grazing management, anthelmintic treatment practices and use of diagnostic tests. RESULTS: A total of 193 responses detailing information on parasite control programmes of 993 equids were analysed. Moxidectin (MOX) and ivermectin or related combination products were the most commonly administered anthelmintics in the preceding 12 months. Treatments licensed for use against cyathostomin encysted larvae and tapeworms were administered by 80% and 90% of respondents, respectively. This was often achieved through indiscriminate use of MOX and MOX-praziquantel products. Faecal egg count (FEC) analysis had been performed on 62% of yards and regular use of FECs reduced annual anthelmintic treatment frequency. Veterinarians had the greatest influence on control practices. While 40% of respondents believed that they practised targeted dosing, this was not associated with delaying treatment beyond the egg reappearance period of the anthelmintic used. CONCLUSIONS: Responses indicated increasing veterinary involvement and use of FECs. The majority of respondents administered anthelmintics licensed against cyathostomin encysted larvae and tapeworms. However, responses suggested that owners did not understand the definition of 'targeted' dosing regimens. POTENTIAL RELEVANCE: The high frequency of MOX use represents a potential risk factor for macrocyclic lactone resistance. As veterinarians were the most influential factor in anthelmintic choice, awareness of macrocyclic lactone resistance and potential risk factors for its development and spread should be incorporated into client advice.

Sensory nerve conduction and somatosensory evoked potentials of the trigeminal nerve in horses with idiopathic headshaking.

BACKGROUND: Idiopathic headshaking (HSK) in horses is a distressing disorder in which the etiology and pathophysiology are unknown. HYPOTHESIS: Differences in sensory function of the trigeminal nerve exist between healthy and affected horses. ANIMALS: Six healthy mature geldings and 6 mature geldings with idiopathic HSK. METHODS: Prospective study. Sensory nerve action and somatosensory evoked potentials studies were performed. The stimulus site comprised the gingival mucosa dorsal to the maxillary canine. A pair of recording electrodes was placed along the sensory pathway of the trigeminal complex at the infraorbital nerve (R1), maxillary nerve (R2), spinal tract of trigeminal (R3), and somatosensory cortex (R4). Sensory nerve action potential latency (ms), amplitude (µV), duration (ms), area under the curve (µVms), and conduction velocity (m/s) were calculated. RESULTS: Threshold for activation of the infraorbital branch of the trigeminal nerve was significantly different between 5 affected (≤ 5 mA) and 6 control horses (≥ 10 mA). After initiation of an action potential, there were no differences in all parameters measured and no differences between left and right sides. A horse with seasonal HSK tested during a time of no clinical manifestations showed a threshold for activation similar to control horses. CONCLUSIONS AND CLINICAL IMPORTANCE: This study confirms involvement of the trigeminal nerve hyperexcitability in the pathophysiology of disease. Further, results might support a functional rather than a structural alteration in the sensory pathway of the trigeminal complex that can be seasonal. The horse could serve as a natural animal model for humans with idiopathic trigeminal neuralgia.

Abnormal plasma neuroactive progestagen derivatives in ill, neonatal foals presented to the neonatal intensive care unit.

REASONS FOR PERFORMING THE STUDY: Increased levels of pregnanes have been reported in foals with neonatal maladjustment syndrome (NMS). These steroids may cross the blood-brain barrier and have depressive effects in the central nervous system leading to behavioural abnormalities and altered states of consciousness in affected foals. OBJECTIVES: The aim of this study was to determine the pregnane profile of foals with NMS and compare it with that of healthy controls and sick, non-NMS foals. STUDY DESIGN: Prospective-clinical study. METHODS: Thirty-two foals with a clinical diagnosis of NMS, 12 foals with other neonatal disorders and 10 healthy control foals were selected for the study. Heparinised blood samples were collected from each group of foals and pregnane and androgen concentrations determined using liquid chromatography mass spectrometry at 0, 24 and 48 h of age. RESULTS: Healthy foals showed a significant decrease in pregnane concentrations over the first 48 h of life (P<0.01). Foals with NMS and sick, non-NMS foals had significantly increased progesterone, pregnenolone, androstenedione, dehydroepiandrosterone and epitestosterone concentrations compared with healthy foals (P<0.05). Progesterone and pregnenolone concentrations of sick, non-NMS foals decreased significantly over 48 h (P<0.05), whereas concentrations in NMS foals remained increased. CONCLUSIONS AND POTENTIAL RELEVANCE: Pregnane concentrations of ill, neonatal foals remain increased following birth, reflecting a delayed, or interrupted, transition from intra- to extra-uterine life. Serial progesterone and pregnenolone measurement may be useful in aiding diagnosis of NMS.

Allopregnanolone infusion induced neurobehavioural alterations in a neonatal foal: is this a clue to the pathogenesis of neonatal maladjustment syndrome?

REASONS FOR PERFORMING THE STUDY: Increased plasma progestagen concentrations have been reported in foals with neonatal maladjustment syndrome (NMS). These steroids may cross the blood-brain barrier and have dampening effects in the central nervous system. OBJECTIVES: To evaluate if the infusion of a progesterone derivative (allopregnanolone) in a healthy neonatal foal would induce clinical signs compatible with NMS. METHODS: A healthy neonatal foal from a healthy mare with a normal gestation (length, no complications), birth and placenta was infused with allopregnanolone to observe its neurobehavioural effects. Heparinised blood samples were collected pre- and post infusion to determine various progestagen concentrations using liquid chromatography mass spectrometry. A second healthy neonatal foal was infused with ethanol and saline for comparison of clinical observations. RESULTS: Infusion of allopregnanolone resulted in obtundation, lack of affinity for the mare and decreased response to external stimuli. These effects were short-lasting and associated with measurable concentrations of progestagens. CONCLUSIONS AND POTENTIAL RELEVANCE: Infusion of a steroid metabolite to a healthy neonatal foal resulted in neurobehavioural alterations compatible with those observed in foals with NMS. These findings suggest that increased progestagen concentrations may be responsible for some of the behavioural changes observed in foals with NMS.

Latent equine herpesvirus-1 in trigeminal ganglia and equine idiopathic headshaking.

BACKGROUND: Trigeminal neuralgia or neuropathic pain has been regarded as a putative cause of idiopathic headshaking in horses. Equine herpesvirus-1 (EHV-1) infection and resultant postherpetic pain have been suggested as a possible cause of such neuropathic pain. HYPOTHESIS/OBJECTIVES: To determine the presence of EHV-1 in the trigeminal ganglia of horses with idiopathic headshaking. ANIMALS: Nineteen horses: control (n = 11, 9 geldings, 2 mares, median age 11 years) and headshaking (n = 8, all geldings, median age 11.5 years) horses were sourced from the equine research herd and caseload at the Veterinary Medical Teaching Hospital. METHODS: Prospective study to determine the presence of EHV-1 latency in trigeminal ganglia of horses with idiopathic headshaking by real-time PCR detection of the glycoprotein B (gB) gene and the DNA polymerase (ORF 30) gene of EHV-1 in the absence of detectable late structural protein gene (gB gene) mRNA. Control horses were used for comparison. A house keeping gene (equine GAPDH) and positive and negative samples for EHV-1 were used for quality control. RESULTS: All samples from control horses and 7 of 8 headshaking horses were negative for EHV-1. One headshaking horse tested positive for a single copy of EHV-1 gene. CONCLUSIONS AND CLINICAL IMPORTANCE: This study does not support a role for EHV-1 infection and presumed postherpetic pain in the etiopathogenesis of equine headshaking.

Potential barriers to veterinary student access to counselling and other support systems: perceptions of staff and students at a UK veterinary school.

Considerable evidence suggests that veterinary surgeons' mental health is often poorer than comparable populations and that the incidence of suicide is higher among veterinary surgeons than the general public. Veterinary students also appear to suffer from high levels of anxiety and stress, and may possess inadequate coping strategies when faced with adversity. Veterinary students may find it difficult to access central university support systems due to their heavy workload and geographical isolation on some veterinary campuses. A previous study of University of Edinburgh fourth-year veterinary students found that support services located several miles from the main veterinary campus was a barrier to students accessing counselling services. Consequently, a pilot project was initiated, which provided a counselling service at the University of Edinburgh's rural Easter Bush veterinary campus one afternoon a week during 2010. As part of the evaluation of this service, web-based questionnaires were delivered via e-mail to all veterinary staff and students towards the end of the 12-month pilot period to evaluate perceptions of barriers to student counselling and to investigate student-valued support services. Questionnaire responses were received from 35 per cent of veterinary students and 52 per cent of staff. Stigmatisation of being unable to cope was a potent inhibitor of seeking support within the veterinary environment, but counselling was perceived as valuable by the majority of staff and students. Provision of an on-site counselling service was considered important for increasing ease of access; however, students viewed friends and family as their most important support mechanism. Workload was cited as the main cause of veterinary student stress. The majority of staff and student respondents perceived veterinary students as having an increased need for counselling support compared with other students.

An update on cyathostomins: anthelmintic resistance and diagnostic tools.

Cyathostomins represent a potential cause of equine morbidity and have become the main focus of endoparasite control in managed horses. All grazing horses are at risk of infection with cyathostomins; therefore, the application of appropriate management measures is essential. Anthelmintics currently comprise the main method of control for equine nematodes and the ready availability of these products in some countries has resulted in their use becoming dissociated from veterinary involvement. This is concerning given the levels of anthelmintic resistance that have been recorded in cyathostomin populations. It is important that veterinarians re-establish control over the implementation of parasite control programmes, a major objective of which should be the preservation of anthelmintic efficacy. This article details the principles of cyathostomin control in horses with particular reference to anthelmintic resistance, and the use and interpretation of diagnostic tests for detecting cyathostomins and identifying anthelmintic resistance.

Preliminary investigation of somatosensory evoked potentials in equine headshaking.

The aim of this study was to develop a technique for recording electrical activity of the equine cerebral cortex following application of a noxious electrical stimulus to the maxillary branch of the trigeminal nerve in order to investigate trigeminal nerve neurophysiology in control and headshaking horses. Triphasic somatosensory evoked potentials (SEPs) were recorded using subcutaneous needle electrodes in four control and four headshaking horses under general anaesthesia. Dural electroencephalography electrodes were used to record SEPs in one further control and one further headshaking horse. Headshaking horses appeared to have decreased middle latency and inter-peak intervals following stimulation of the trigeminal nerve compared with control horses, supporting abnormal trigeminal nerve physiology in equine headshaking.

Use of a gonadotrophin-releasing hormone vaccine in headshaking horses.

The aim of this study was to investigate the use of a gonadotrophin-releasing hormone (GnRH) vaccine in the treatment of headshaking in horses. Fifteen geldings received two doses of the GnRH vaccine four weeks apart. Serum was collected before and after vaccination to measure concentrations of luteinising hormone (LH) (10 horses) and follicle-stimulating hormone (FSH) (six horses). Owners recorded the frequency of seven common headshaking behaviours using a visual analogue scale (VAS) before vaccination and at two, four, eight, 12, 16 and 20 weeks after vaccination. Serum LH (P=0.008) and FSH (P=0.03) concentrations decreased significantly following vaccination. Although approximately one-third of the owners reported a subjective improvement in headshaking, serial scoring did not indicate a reduction in headshaking behaviours following vaccination with a commercial GnRH vaccine. Vaccination reactions were observed in four of 15 horses (27 per cent), including one case of severe, presumed immune-mediated, myositis.

Large intestinal mast cell count and proteinase expression is associated with larval burden in cyathostomin-infected horses.

REASONS FOR PERFORMING STUDY: Cyathostomins are the principal pathogenic nematode of equidae worldwide. In other species mast cell (MC) proteinases, in particular chymases, appear to have protective roles. Knowledge of the equine intestinal immune response to cyathostomins is limited. OBJECTIVE: To investigate MC numbers and proteinase expression in equine cyathostomin-infected large intestine. HYPOTHESIS: MC populations in the large intestine are positively associated with cyathostomin burden and predominantly express chymase. METHODS: The caecal cyathostomin burden of naturally infected horses (n = 25) was determined by luminal counts and pepsin digest (mural count). MC were identified and enumerated in caecal tissue using toluidine blue (TB). Immunofluorescent labelling with polyclonal rabbit antibodies was used to demonstrate expression of equine tryptase and the chymase equine mast cell proteinase-1 (eqMCP-1) in Carnoy's fixed caecal sections. RESULTS: Significant positive linear relationships were found between TB-stained mucosal and submucosal MC counts and total cyathostomin burden (P<0.001, r² >36%), and both luminal (P<0.010, r² >25%) and mural (P<0.001, r² >36%) larval counts. Similar relationships were found with mucosal and submucosal chymase and tryptase-labelled MC counts (total: P<0.004, r² >29%; luminal: P<0.004, r² >30%; and mural: P<0.030, r² >19%). With all three MC labels, mean MC counts were higher in the submucosa compared to the mucosa (P<0.001). All caecal MC appeared to express chymase, with a small number of MC expressing both tryptase and chymase. CONCLUSIONS AND POTENTIAL RELEVANCE: Large intestinal MC counts are significantly associated with cyathostomin burden, with a predominance of chymase-positive MC. The burden is significantly associated with expression of MC proteinases, supporting their likely involvement in the intestinal immune response to cyathostomin infection. Further work to investigate the kinetics of proteinase expression, the possibility of differential proteinase expression and the role of these MC proteinases is warranted.

Cytological analysis of equine bronchoalveolar lavage fluid. Part 1: Comparison of sequential and pooled aliquots.

The aim of this study was to investigate whether initial equine bronchoalveolar lavage fluid (BALF) aliquots were more representative of bronchial cytology that bronchiolar and alveolar cytology. Cell viability and total nucleated (TCC), differential (DCC) and absolute cell counts of cytocentrifuged preparations of 3 sequentially collected BALF aliquots (Aliquots 1-3) were compared with those of pooled BALF (Aliquot 4) to assess whether all aliquots were representative of the lavaged lung segment. BALF samples (n = 21) were collected from control horses (n = 5) or heaves-affected horses (n = 5). There were nonsignificant trends of increasing TCC and absolute macrophage count from Aliquot 1 to Aliquot 3 and significant differences in macrophage (P<0.05) and lymphocyte (P<0.01) DCC among aliquots of all horses; however, no linear trend in this DCC data was observed. There was a significant decrease in mast cell DCC (P<0.01) from Aliquot 1 to Aliquot 3 in control horses. Cell viability did not differ significantly among aliquots. There was no diagnostically significant difference in TCC, DCC, absolute cell counts or cell viability, among sequential and pooled BALF aliquots and, therefore, all aliquots can be considered to represent the cytology of the lavaged lung segment. This indicates that even if BALF recoveries are very low, cytological analysis of samples will be of diagnostic value.

Cytological analysis of equine bronchoalveolar lavage fluid. Part 2: Comparison of smear and cytocentrifuged preparations.

The aim of this study was to develop a diagnostically useful smear method for preparation of equine bronchoalveolar lavage fluid (BALF) for use by practitioners. A smear method for equine BALF preparation which included the addition of serum was developed, and cell morphology, differential cell counts (DCC) and repeatability of counting DCC compared with those of cytocentrifuged BALF preparations. BALF samples (n = 21) were collected from 5 control horses and 5 heaves-susceptible horses. Smear preparations of BALF produced smaller, darker, staining cells, making cytological identification more difficult than on cytocentrifuged preparations. There was a significantly higher (P<0.01) macrophage DCC and lower lymphocyte DCC on cytocentrifuged compared to smear preparations. Mast cell and eosinophil DCC were significantly higher (P<0.05) on cytocentrifuged compared to smear preparations of BALF. Smear preparations were shown to be reliable for the cytological diagnosis of equine neutrophilic pulmonary disease and offer practitioners an alternative to sending equine BALF to a laboratory for processing and cytological analysis.

Cytological analysis of equine bronchoalveolar lavage fluid. Part 3: The effect of time, temperature and fixatives.

Bronchoalveolar lavage fluid (BALF) samples are often subject to time delays, possibly with temperature fluctuations, between collection and processing. The aim of this study was to evaluate the effects of time, temperature and 2 different fixatives on equine BALF cytology, in order to develop guidelines for optimal equine BALF storage conditions. Total nucleated cell count (TCC), differential cell counts (DCC), absolute cell counts (ACC), cell viability, cell morphology and bacterial growth of BALF samples stored at 4, 18 (+/- addition of formalin- or alcohol-based fixatives) and 38 degrees C were monitored serially over a 72 h period. The time taken for a significant reduction in TCC and cell viability of unfixed BALF samples decreased as the storage temperature increased. There was no diagnostically significant difference in DCC or ACC over this time-course at any temperature. Unfixed BALF samples showed significant bacterial growth by 24 h at 4 degrees C, and 8 h at 18 and 38 degrees C; and poor morphology by 48 h at 4 degrees C, 24 h at 18 degrees C and 8 h at 38 degrees C. Fixed BALF samples showed poor morphology with Leishman's stain compared to unfixed samples.

Clinical and endoscopic evidence of progression in 152 cases of equine recurrent laryngeal neuropathy (RLN).

Examination of the long-term histories and clinical findings was performed in 351 horses suffering from recurrent laryngeal neuropathy (RLN) to examine for possible evidence of progression of this disorder. Fifty-two out of 351 cases (15%) had evidence of progression of the degree of laryngeal dysfunction over a median period of 12 months (range 1.5-48 months) with the onset of progression occurring at median age 7 years. In 30 cases, there was both endoscopic (median deterioration of 3 endoscopic grades; range 1-5 grades) and clinical evidence, with 29 (97%) of these horses concurrently developing sudden-onset, abnormal exercise-related respiratory 'noises' and 13 (43%) concurrently reporting reduced exercise performance. In the remaining 22 horses there was solely clinical evidence of RLN progression, including the sudden onset of abnormal exercise-related respiratory sounds in 16 (73%) and the worsening of such sounds in 6 (23%), associated with reduced exercise performance in 13 (59%) of these 22 cases. Endoscopically, 13 (59%) of the latter 22 cases had marked (total or almost total) RLN that did not appear compatible with their previous exercise-performance histories. This evidence of progression of RLN may be of particular significance in disputes concerning horses that are apparently normal at pre-purchase examination but are later shown to have RLN and also in the surgical treatment of less severe cases of RLN.

Laryngeal paralysis: a study of 375 cases in a mixed-breed population of horses.

Referred cases (n = 375) of laryngeal paralysis (1985-1998) from a mixed-breed equine population included 351 (94%) cases of recurrent laryngeal neuropathy (RLN) (idiopathic laryngeal hemiplegia) and 24 cases (6%) of laryngeal paralysis from causes other than RLN. Laryngeal movements were classified endoscopically into one of 6 grades, in contrast to the usual 4 grades. The RLN cases had a median grade 4 laryngeal paralysis, of which 96% were left-sided, 2% right-sided and 2% bilaterally affected. RLN cases included 204 (58%) Thoroughbred, 96 (27%) Thoroughbred-cross, 23 (7%) draught, 16 (5%) Warmbloods and 10 (3%) other breeds, including only 4 (1%) ponies. The median age of RLN cases at referral was 6 years (range 2-12) and their median height was 170.2 cm. The work of RLN horses included National Hunt racing (42%), flat racing (1%), hunting (19%), eventing (16%) and miscellaneous work (22%). Reported presenting signs in RLN-affected horses included abnormal exercise-related respiratory sounds in 90% and reduced exercise tolerance in only 64%. However, many horses were referred before their exercise tolerance could be fully assessed. Forty percent of the RLN cases had intercurrent disorders, including 10% with additional upper respiratory and 7% with lower respiratory tract diseases. The 24 nonidiopathic RLN cases included 12 with bilateral laryngeal paralysis, 11 (92%) of which were ponies. Bilateral laryngeal paralysis occurred with hepatic encephalopathy in 7 cases and following general anaesthesia in 2 cases. The 12 cases of acquired unilateral laryngeal paralysis included 7 caused by guttural pouch mycosis.