Electroencephalographic examination of epileptic dogs under propofol restraint

The main aim of this study was to identify interictal epileptiform discharges in a group of dogs with seizures of known aetiology (symptomatic epilepsy, SE) and in dogs with idiopathic epilepsy (IE). Propofol was used for chemical restraint in all dogs. We found electroencephalographic (EEG) changes that could be considered epileptiform discharges (EDs) in 5 out of 40 dogs (12.5%). The EEG changes identified were spikes in four cases and periodic epileptiform discharges in one case. All EDs were seen in the SE group. We conclude that the interictal electroencephalographic examinations of propofolanaesthetised dogs suffering from IE and SE rarely show epileptic discharges and that the diagnostic value of such EEGs in the work-up for epilepsy seems to be low as epileptic discharges were unlikely to be detected. However, positive findings are more likely to be connected with SE. We found frequent, transient EEG phenomena (spindles, K-complexes, vertex waves, positive occipital sharp transients of sleep, cyclic alternating patterns), which are non-epileptic but their differentiation from epileptic phenomena is challenging.     

Epilepsy in horses: Aetiological classification and predictive factors

Reasons for performing the study: In contrast with reports in man and small animals, a systematic classification of seizures in horses is lacking. Objectives: The purpose of this study was to classify seizures based on their aetiology and to characterise epilepsy in 104 horses presented for seizures at the Ohio State University Veterinary Medical Center between 1988 and 2009. Methods: In a retrospective observational study, seizures were classified by aetiology based on history, clinical observations, diagnostic investigations (e.g. electroencephalograms, cerebrospinal fluid and computed tomography imaging of the head) and post mortem examinations, when available. Univariate and multivariate logistic regression analyses were performed. Results: Epilepsy (i.e. 2 or more recurrent seizures) was identified in 70% of cases, and further classified as symptomatic (i.e. structural brain pathology, 35.6% of cases), cryptogenic (i.e. unknown, 54.8% of cases) and idiopathic (i.e. suspected genetic predisposition, 2.7% of cases). Normal neurological examination on admission, the presence of seizures unprovoked by any identified factors and paroxysmal epileptiform activity on electroencephalogram recordings were all strongly (P<0.05) correlated with epilepsy on univariate analysis. For a horse with generalised seizures, the odds of having epilepsy was 7 times lower compared with a similar horse with partial seizures (P<0.05) in multivariate modelling. Conclusions: Seizure aetiology was symptomatic or cryptogenic in most horses, whereas reactive seizures and idiopathic epilepsy were less common. Potential relevance: This study is the first attempt to classify seizures and to characterise epilepsy in a referral-based equine population. Predictive factors of epilepsy in horses were similar to those reported in other species and may assist the clinician with the early diagnosis of epilepsy.     

Behavioural assessment of pain in 66 horses,with and without a bit

Horses can be ridden with or without a bit. Comparing the behaviour of the same horse in different modes constituted a ‘natural experiment’. Sixty-nine behaviours in 66 bitted horses were identified as induced by bit-related pain and recognised as forms of stereotypic behaviour. A prototype questionnaire for the ridden horse was based on 6 years of feedback from riders who had switched from a bitted to a bit-free bridle. From a template of 69 behavioural signs of pain derived from answers to the questionnaire, the number of pain signals shown by each horse, first when bitted and then bit-free, was counted and compared. After mostly multiple years of bit usage, the time horses had been bit-free ranged from 1 to 1095 days (median 35). The number of pain signals exhibited by each horse when bitted ranged from 5 to 51 (median 23); when bit-free from 0 to 16 (median 2). The number of pain signals for the total population when bitted was 1575 and bit-free 208; an 87% reduction. Percentage reduction of each of 69 pain signals when bit-free, ranged from 43 to 100 (median 87). The term ‘bit lameness’ was proposed to describe a syndrome of lameness caused by the bit. Bit pain had a negative effect on proprioception, i.e. balance, posture, coordination and movement. Only one horse showed no reduction in pain signals when bit-free. The welfare of 65 of 66 horses was enhanced by removing the bit; reducing negative emotions (pain) and increasing the potential to experience positive emotions (pleasure). Grading welfare on the Five Domains Model, it was judged that – when bitted – the population exhibited ‘marked to severe welfare compromise and no enhancement’ and – when bit-free – ‘low welfare compromise and mid-level enhancement.’ The bit-free data were consistent with the ‘one-welfare’ criteria of minimising risk and preventing avoidable suffering.     

Use of electromyography for the diagnosis of equine hyperkalemic periodic paresis.

The use of electromyography (EMG) as a diagnostic aid for equine hyperkalemic periodic paresis (EHPP) was investigated in seven affected and seven control horses. Affected horses were confirmed positive for EHPP either by elevated serum potassium concentration with clinical signs of myotonia, or by inducing hyperkalemia and clinical signs using oral potassium chloride challenge. All horses were asymptomatic at the time EMG was performed, using bipolar fine wire needle electrodes. The myopotentials were recorded on magnetic tape and displayed on paper charts for analysis. Insertional and resting activity were recorded from the right supraspinatus, triceps, extensor carpi radialis and gluteal muscles in standing horses. Myotonic discharges were seen in six of seven affected horses but not in any of the controls. All seven affected horses and two control horses had prolonged insertional activity. Five out of seven affected horses and one control horse displayed spontaneous motor unit discharges unrelated to recording electrode movement. Myoelectrical potentials containing closely timed muscle potentials, i.e. doublets, were found in all affected horses, with four of seven affected horses also showing triplets. These potentials were not observed in any of the controls. No obvious difference in activity was observed among the four muscle sites tested. It is concluded that EMG is a safe and useful tool for diagnosing EHPP in horses not currently displaying clinical signs. Myotonic discharges and doublets appear to be the most diagnostically significant electromyographic abnormalities in EHPP affected horses.     

Diagnostic validity of electroencephalography in equine intracranial disorders

Electroencephalography (EEG) is a valuable diagnostic test to identify functional disturbances in brain activity. The purpose of this study was to assess the validity of EEG as a diagnostic indicator of intracranial diseases in horses. The validity of EEG was estimated by comparing clinical, clinicopathologic, and histopathologic findings to EEG findings in 20 horses examined for seizures. collapse, or abnormal behavior between 1984 and 1997. A bipolar left-to-right, back-to-front montage and a bipolar circular montage were recorded from sedated (4) and anesthetized (16) horses. Visual and semiquantitative masked analysis of EEG recording Ist was validated on 10 horses presented for problems other than intracranial diseases. EEG pattern was normal in 7 of the 20 clinically affected horses. Abnormal EEG patterns included high-voltage slow waves and discrete paroxysmal activity with or without generalized activity in 13 horses. Histopathologic diagnoses in 10 horses included meningoencephalitis, neuronal necrosis, congenital anomalies. cerebral edema. and abscess. All of these horses had abnormal EEG patterns (sensitivity, 100%) with a positive neuroanatomic correlation in 7 animals. Localization of histopathologic and EEG abnormalities did not correlate in 15% of the horses (3/20). The cause of neurologic signs could not be explained at postmortem examination in 10 animals and the EEG pattern was normal in 7 of these horses (specificity, 70%). In conclusion, equine EEG was a sensitive tool in the diagnosis of intracranial disorders.     

Idiopathic epilepsy in 125 dogs: a long-term study. Clinical and electroencephalographic findings

Well-documented cases of confirmed idiopathic epilepsy in 125 dogs were evaluated retrospectively. Forty-six breeds (each with no sex predisposition) were examined. Although dogs of all ages were affected, the peak value for the onset of first seizure was between one and five years. Approximately 75 per cent of animals had generalised grand mal type seizures with loss of consciousness. Preictal and postictal phases were present in the majority of dogs. Interictal electroencephalographic recordings of 37 anaesthetised dogs were statistically analysed. High frequency and low amplitude paroxysmal discharges with either a focal or generalised distribution were found in the majority of these dogs. Possible causes for this variation from dog to dog were analysed. It was concluded that, despite anaesthesia, electroencephalographic features were consistent and unique in dogs with idiopathic epilepsy.     

Acoustic communication in the domestic horse (Equus caballus)

Equine vocalization and acoustic sounds can communicate a horse’s emotional state, physiological state, and situation to other individuals, including other horses and humans. These vocalizations and acoustic sounds can be divided into several types. The whinny, nicker, squeal, blow, snore, snort, roar, and groan are typical types of horse vocalizations and acoustic sounds. The sound localization thresholds of horses are markedly poorer than those of other large mammals, such as humans and elephants. The audiogram of horse has shown their best sensitivity and hearing range in which it perceives sound. Laryngeal diseases, such as laryngeal hemiplegia, dorsal displacement of the soft palate, and alar fold paralysis, can cause laryngeal sounds in the upper airway. The analyses of horses’ vocalizations and laryngeal sounds that are reviewed in this article were conducted with computer-aided analysis programs using spectrograms and spectra that evaluate several parameters, including amplitude, fundamental frequency, duration, and formants. Laryngeal sound analysis could be a useful method for diagnosing upper airway diseases. This article presents a review of the literature describing scientific analyses of horse vocalizations and acoustic sounds to elucidate equine acoustic communications and aid in the development of horse-human bonds.     

Brain stem auditory-evoked response in the nonanesthetized horse and pony

The brain stem auditory-evoked response (BAER) was measured in 10 horses and 7 ponies under conditions suitable for clinical diagnostic testing. Latencies of 5 vertex-positive peaks and interpeak latency and amplitude ratio on the 1st and 4th peaks were determined. Data from horses and ponies were analyzed separately and were compared. The stimulus was a click (n = 3,000) ranging from 10- to 90-dB hearing level (HL). Neither horses nor ponies responded with a BAER at 10 dB nor did they give reliable responses at less than 50 dB. The 2nd of the BAER waves appeared in the record at lower stimulus intensities than did the 1st wave for the horse and pony. Horses and ponies had a decreasing latency for all waves, as a result of increasing stimulus intensity. Latencies were shorter for the ponies than for the horses at all stimulus intensities for the 1st, 2nd, 3rd, and 4th waves, but not the 5th wave. At 60-dB HL, the mean latencies for the 1st through 5th wave, respectively, for the horse were 1.73, 3.08, 3.93, 4.98, and 6.00 ms and for the pony 1.48, 2.73, 3.50, 4.56, and 6.58 ms. Interpeak latencies, 1st to 4th wave, averaged 3.22 ms (horse) and 3.11 ms (pony) for all stimulus intensities from 50- to 90-dB HL and had a tendency to decrease slightly as stimulus intensity increased. Amplitude ratios (4th wave/1st wave) were less than 1 for all stimulus intensities in the horse. In the pony, the ratio was less than 1 at greater than or equal to 70-dB HL and greater than 1 at less than or equal to 60-dB HL.     

Focal epilepsy in the Belgian shepherd: evidence for simple Mendelian inheritance

Objectives : To establish the mode of inheritance and describe the clinical features of epilepsy in the Belgian shepherd, taking the outset in an extended Danish dog family (199 individuals) of Groenendael and Tervueren with accumulated epilepsy. Methods : Epilepsy positive individuals (living and deceased) were ascertained through a telephone interview using a standardised questionnaire regarding seizure history and phenomenology. Living dogs were invited to a detailed clinical evaluation. Litters more than five years of age, or where epilepsy was present in all offspring before the age of five, were included in the calculations of inheritance. Results : Out of 199 family members, 66 dogs suffered from epilepsy. The prevalence of epilepsy in the family was 33%. Fifty‐five dogs experienced focal seizures with or without secondary generalisation, while four dogs experienced primary generalised seizures. In seven dogs, seizures could not be classified. The mode of inheritance of epilepsy was simple Mendelian. Clinical Significance : This study identified that the Belgian shepherd suffers from genetically transmitted focal epilepsy. The seizure phenomenology expressed by family members have a strong resemblance to what has been reported for familial partial (focal) epilepsy in humans with variable foci with suggestion of linkage to chromosome 2 and chromosome 22q12.     

MAGNETIC RESONANCE IMAGING FEATURES OF EQUINE NIGROPALLIDAL ENCEPHALOMALACIA

Magnetic resonance imaging (MR) was used to make a diagnosis of equine nigropallidal encephalomalacia in a horse. Equine nigropallidal encephalomalacia is a neurodegenerative disease that has many characteristics with Parkinson-like diseases in humans. Historically, horses were euthanized based on clinical signs and exposure to the toxic weed, yellow star thistle (Centaurea solstitialis). Previously, the disease has only been confirmed on necropsy. MR imaging can provide accurate and sensitive visualization of typical lesions seen in the brain of horses affected with equine nigropallidal encephalomalacia. Lesions were seen on T1-weighted, T2-weighted and proton density images. There was no contrast enhancement following Gd-DTPA administration. Lesions seen on MR were confirmed at necropsy. Using MR to confirm a diagnosis of equine nigropallidal encephalomalacia will prevent unnecessary suffering of horses and expense to owners that would otherwise incur, while further diagnostics are performed.     

Preliminary results suggest an influence of psychological and physiological stress in humans on horse heart rate and behavior

People may involuntarily emit fear or distress signals when around horses, and interpreting how horses respond to these messages is important, particularly for human safety around horses. No studies have been done to determine if horses can differentiate between humans who are physiologically stressed (e.g., after exercising) as opposed to psychologically stressed (e.g., afraid). Horses (N = 10) loose in a round pen were randomly subjected to the presence of a stationary blindfolded human in each of 4 treatments: (1) calm human comfortable around horses (CALM), (2) physically stressed human (PHYS; exercised to 70% maximum heart rate [HR]), (3) psychologically stressed human (PSYCH; afraid of horses), or (4) no human (CONTROL). Both humans and horses were equipped with an HR monitor. Physiological and behavioral observations (gait, head position relative to the withers, distance and orientation toward human) were recorded and analyzed using a mixed model with horse and human as random effects. Increasing human fearfulness was associated with a decrease in horse HR (P = 0.0156). Horses moved at a slower gait in PSYCH (P < 0.0001), and horse head position was lower during PHYS and PSYCH compared with CALM or CONTROL (P < 0.0001). Human HR was highest in PHYS (P < 0.0001) and decreased over time in all treatments. Human HR increased when the horse was facing away (P = 0.0395). Overall, horses appear less stressed in the presence of a stationary fearful or physically stressed human than a calm person. Thus, horses in the presence of fearful humans, particularly where participants may not be comfortable around horses, should not pose any additional risk provided normal safety precautions are used.     

Electroencephalographic alterations in a mare with presumed intermittent neuroglycopenia caused by severe hypoglycaemia-associated with nonislet cell tumour

The focus of this report was to document the electroencephalogram (EEG) findings associated with nonislet cell tumour-induced hypoglycaemia (NICTH) in a racing Thoroughbred mare subsequently diagnosed with renal carcinoma and carcinomatosis. We evaluated cortical cerebral activity and confirmed paroxysmal activity consistent with subclinical seizures by performing an EEG prior to onset of clinical signs of seizures. We showed that the electrical activity pattern progressed in a similar fashion as in humans with severe, progressive hypoglycaemia and presumed neuroglycopenia. The glycaemic threshold for abnormalities detected in EEG showed that abnormal electrical cortical activity appeared when blood glucose dropped to 44 mg/dL (2.4 mmol/L) and paroxysmal activity spread, becoming generalised when blood glucose dropped to 23 mg/dL (1.3 mmol/L). NICTH is an uncommon paraneoplastic phenomenon in several species. In horses, NICTH has been reported most frequently in primary renal tumours, followed by primary hepatic tumours. This report highlights the importance of investigating the possibility of hypoglycaemia in cases of horses that present altered state of consciousness with or without intermittent seizures. This case report also highlights that the diagnostic work-up for horses presenting with episodic hypoglycaemia should comprise investigation of possible neoplasia, as paraneoplastic hypoglycaemia should be included in the list of differentials of horses with hypoglycaemia.     

Distribution of 5'-nucleotidase and gamma glutamyl transferase activities in the tissues of the horse

In the horse, 5'-nucleotidase (5'-NT) activity is found mainly in homogenates of lung, kidney, small intestine, mammary gland, liver and pancreas. Lower activities are present in brain and muscle. Activity can be demonstrated histochemically in the glomeruli and tubules of the kidney, in the sinusoidal borders of the hepatocytes and the bile duct epithelium as well as in the blood vessels of all organs. There is no significant difference between the 5'-NT activity in serum and plasma of normal horses and of horses suffering from a range of orthopaedic conditions. Previous findings that gamma glutamyl transferase activity is greatest in kidney and high in liver and pancreas have been confirmed.     

Exploring lay perceptions of the causes of crib‐biting/windsucking behaviour in horses

Reasons for performing study: Crib‐biting/windsucking behaviour has important consequences for equine health and welfare. Lay perceptions of health and illness are of interest to medical sociologists, providing important information to medical practitioners, but have infrequently been applied in veterinary research. Objectives: To demonstrate how lay epidemiology can be applied within veterinary research by exploring the lay perceptions regarding the causes of crib‐biting/windsucking behaviour in horses. Methods: Informants were recruited from professional and amateur horse owners who had or had not owned/cared for a horse that exhibited crib‐biting/windsucking behaviour. In‐depth interviews were used to examine perceptions about the development of this behaviour within each group until a ‘saturation’ of themes emerged. Results: The main themes that emerged as causes of crib‐biting/windsucking behaviour were ‘boredom’, ‘stress’ and ‘habit/addiction’. In the group of owners/carers who did not have direct experience of this type of behaviour, ‘copying’ from other horses emerged as a strong theme and they stated that they would not wish to own a crib‐biting/windsucking horse. In contrast, those who had direct experience of horses demonstrating this behaviour did not believe copying was a cause based on their own observations and would not be put off purchasing or caring for another horse displaying this behaviour. Conclusions: Perceptions about what causes crib‐biting/windsucking was influenced by whether or not informants had personal experience of horses demonstrating this behaviour. The three main themes that emerged have some justification based on current research and highlight the need for further investigation into the underlying pathophysiology of crib‐biting/windsucking behaviour. Potential relevance: Qualitative approaches to health, disease and behaviour have an important role in the medical field and are applicable to veterinary research.     

Qualitative and quantitative characteristics of the electroencephalogram in normal horses after sedation

Background

The administration of certain sedatives has been shown to promote sleep in humans. Related agents induce sleep‐like behavior when administered to horses. Interpretation of electroencephalograms (EEGs) obtained from sedated horses should take into account background activity, presence of sleep‐related EEG events, and the animal's behavior.

Hypothesis

Sedatives induce states of vigilance that are indistinguishable on EEGs from those that occur naturally.

Animals

Six healthy horses.

Methods

Digital EEG with video was recorded after administration of 1 of 4 sedatives (acepromazine, butorphanol, xylazine, or detomidine). Serum drug concentrations were measured. Recordings were reviewed, states were identified, and representative EEG samples were analysed. These data were compared with data previously obtained during a study of natural sleep.

Results

Butorphanol was associated with brief episodes resembling slow wave sleep in 1 horse. Acepromazine led to SWS in 3 horses, including 1 that also exhibited rapid eye movement sleep. Periods of SWS were observed in all horses afer xylazine or detomidine administration. Normal sleep‐related EEG events and heart block, occurred in association with SWS regardless of which sedative was used. Spectral data varied primarily by state, but some differences were observed between sedative and natural data.

Conclusions and Clinical Importance

Qualitatively, EEG findings appeared identical whether sedation‐induced or naturally occurring. The startle response and heart block associated with some sedatives may be related to sleep. Alpha₂ agonists can be used to obtain high quality EEGs in horses, but acepromazine does not promote a relaxed state in all animals.     

Candidate genes for physical performance in the horse

Intense selection for speed, endurance or pulling power in the domestic horse (Equus caballus) has resulted in a number of adaptive changes in the phenotype required for elite athletic performance. To date, studies in humans have revealed a large number of genes involved in elite athletic performance, but studies in horses are rare. The horse genome assembly and bioinformation tools for genome analyses have been used to compare human performance genes with their equine orthologues, both to retrieve pathways for these genes and to investigate their chromosomal distribution. In this review, 28 candidate genes for equine performance are presented that have polymorphisms associated with human elite athletic performance and may have impact on athletic performance in horses. A significant accumulation of candidate genes was found on horse chromosomes 4 and 12. Genes involved in pathways for focal adhesion, regulation of actin cytoskeleton, neuroactive ligand-receptor interaction, and calcium signalling were over-represented. Genome-wide association studies for athletic performance in horses may benefit from the strong conserved synteny of the chromosomal arrangement of genes in humans and horses.     

Behaviour of the false rig: causes and treatments

The false rig is a castrated horse which shows masculine behaviour of one sort or another. The behaviour patterns reported to the author by owners of such animals and the possible causes are discussed here. Some such horses can show all the behaviour patterns of the entire, including erection and intromission. Evidence is presented that the behaviour is not hormonally induced or hormone dependent. The thesis is put forward that the behaviour shown is part of the normal social interaction between horses and possible treatments are discussed in the light of this possibility.     

Using magnetic resonance imaging to diagnose nondisplaced fractures of the second phalanx in horses

Two horses presented with a history of severe lameness that was localised to the area around the second phalanx (P2) of one forelimb. Radiographs of the second phalanx of both horses were unremarkable, apart from some smooth periosteal new bone production on the dorsum of P2. Magnetic resonance imaging revealed a non-displaced fracture of P2 in both horses. One horse was euthanased because of a poor prognosis for racing, but the second horse was treated conservatively and salvaged for breeding. Magnetic resonance imaging is a newer imaging modality in horses and may be useful in diagnosing cases of obscure lameness.     

The recognition of pain and learned behaviour in horses which buck

Bucking behaviour in horses is potentially dangerous to riders. There is limited information about how bucking behaviour should be investigated by veterinarians. The objectives of this article are to define bucking behaviour, to review the literature relating to bucking and allied behaviours in horses and describe personal observations and to describe an approach to clinical investigation and management strategies. A literature review from 2000 to 2020 was performed via search engines and additional free searches. A buck is an upward leap, usually in addition to forward propulsion, when either both hindlimbs or all four limbs are off the ground with the thoracolumbosacral region raised. Bucking often occurs as a series of such leaps and different manifestations include ‘pronking’, ‘bronking’ and ‘fly bucking’. Causes include excitement, exuberance, defensive behaviour associated with fear, learned behaviour through negative reinforcement or a reaction to musculoskeletal pain. Specific causes of pain include an ill-fitting saddle or girth, thoracolumbar pain, girth region pain, sternal or rib injury, neuropathic pain, sacroiliac joint region pain, referred pain and primary hindlimb lameness. Any of these may be compounded by a rider who is fearful, poorly balanced or crooked. Determination of the underlying cause requires a comprehensive clinical assessment, including assessment of saddle fit for horse and rider and suitability of the horse–rider combination. In some horses, identification of a primary source of pain allows targeted treatment and resolution of pain, but careful retraining is crucial. An understanding of learning behaviour is required for successful rehabilitation. It was concluded that identification of the cause of bucking may enable treatment of primary pain which, when combined with retraining, results in management of bucking behaviour. However, in a minority of horses, dangerous bucking behaviour cannot be reliably resolved, requiring retirement or euthanasia of the horse.