Abstract The cardiac conduction system in large carnivores, such as the African lion (Panthera leo), represents a significant knowledge gap in both veterinary science and in cardiac electrophysiology. Short QT intervals have been reported from zoo‐kept, anaesthetized lions, and our goal was to record the first ECGs from wild, conscious lions roaming freely, and compare them to zoo‐kept lions under the hypothesis that short QT is unique to zoo‐kept lions. Macroscopic and histological examinations were performed on heart tissue removed from nine healthy zoo lions. ECGs were recorded from the nine anaesthetized zoo‐kept lions, and from 15 anaesthetized and conscious wild lions in Africa. Our histological and topographical description of the lion's heart matched what has previously been published. In conscious lions, the ECG recordings revealed a mean heart rate of 70 ± 4 beats/min, with faster heart rates during the night. PQ and QT intervals were heart rate dependent in the conscious lions. Interestingly, QT intervals recorded in wild lions were markedly longer than QT intervals from zoo lions (398 ± 40 vs. 297 ± 9 ms, respectively; P < 0.0001). Anaesthesia or heart rate did not account for this difference. We provide a comprehensive description of the cardiac anatomy and electrophysiology of wild and zoo‐kept lions. QT intervals were significantly shorter in zoo lions, suggesting functional disparities in cardiac electrophysiology between wild and zoo‐kept lions, potentially related to physical fitness. These findings underscore the plasticity of cardiac electrophysiology and may be of value when reintroducing endangered species into the wild and when managing lions in human care.

BACKGROUND:The Purkinje fibers convey the electrical impulses at much higher speed than the working myocardial cells. Thus, the distribution of the Purkinje network is of paramount importance for the timing and coordination of ventricular activation. The Purkinje fibers are found in the subendocardium of all species of mammals, but some mammals also possess an intramural Purkinje fiber network that provides for relatively instantaneous, burst-like activation of the entire ventricular wall, and gives rise to an rS configuration in lead II of the ECG.AIM:To relate the topography of the horse heart and the distribution and histology of the conduction system to the pattern of ventricular activation as a mechanism for the unique electrical axis of the equine heart.METHODS:The morphology and distribution of the cardiac conduction system was determined by histochemistry. The electrical activity was measured using ECG in the Einthoven and orthogonal configuration.RESULTS:The long axis of the equine heart is close to vertical. Outside the nodal regions the conduction system consisted of Purkinje fibers connected by connexin 43 and long, slender parallel running transitional cells. The Purkinje fiber network extended deep into the ventricular walls. ECGs recorded in an orthogonal configuration revealed a mean electrical axis pointing in a cranial-to-left direction indicating ventricular activation in an apex-to-base direction.CONCLUSION:The direction of the mean electrical axis in the equine heart is determined by the architecture of the intramural Purkinje network, rather than being a reflection of ventricular mass.

Background: Fractures in the limbs of racehorses are common, resulting among other factors, as the result of repeated ground reaction forces on bones and joints, leading to catastrophic failure. Aim: To quantify ground impact transmission through the limb bones of un-shod healthy horses using the non-invasive technique of acoustic myography (AMG). Methods: Four sites were selected for AMG measurements at the walk and trot, hoof wall (site 1) and sites 2 - 4, metacarpal 3, carpals and the radius of the left forelimb of two healthy horses. Measurements were on both rubber and concrete. AMG of the equine hind limb suspensory system was made and analyzed (amplitude and timing) for the proximal suspensory ligament (PSL) and the SDFT/DDFT. Results: AMG signal amplitude at site 1 (1.5 ± 0.2 versus 1.1 ± 1.5) was not found to be significantly different at the trot compared to the walk; however, sites 2, 3 and 4 were all significantly different when compared between the two gaits; site 2 P = 0.008; site 3 P = 0.006; site 4 P = 0.005. AMG signals recorded on the rubber surface had smaller amplitude than the equivalent signal and site on the concrete surface. Ground Reaction Force (GRF) transmission in the equine forelimb was 22 m/sec, whilst that of the hind limb suspensory system was 25 m/sec. Conclusion: Findings indicate that GRFs are transmitted proximally along the limb at considerable speeds, that they are dampened by tissues and structures in the limb, and that the GRFs are present and detectable proximal to the fetlock joint.

Seven superficial myofascial kinetic lines have been described earlier in horses in a comparative dissection study to the human lines. The lines act as an anatomical basis for understanding locomotion, stabilization, and posture. Further dissections verified three profound equine lines comparable to those described in humans and a fourth line not described previously. Forty-four horses of different breed and gender were dissected, imaged and video recorded. The horses were euthanized due to reasons not related to this study. A Deep Ventral Line (DVL) very similar to that in the human was verified in these studies. The line spans from the insertion of the profound flexor tendon in the hindlimb to the base of the cranium and oral part of the cavities of the head. It includes the profound, hypaxial myofascial structures, the ventral coccygeal muscles, the psoas muscles, the diaphragm, the longus colli/capitis muscles and the ventral capital muscles. The inner lining of the pelvic, abdominal and thoracic cavities with all the organs, vessels and nerves are also included. The line is closely connected to the autonomic nervous system by the vagus nerve, the pelvic nerves, the sympathetic trunk and several of the prevertebral nerves and ganglia. The new line identified in this study, is a Deep Dorsal Line (DDL), which starts in the dorsal tail muscles. It comprises myofascial structures of the spinocostotransversal system from the tail to the head including the nuchal ligament. It connects to the dura mater and has a major role in controlling the motion and stabilization of the Columna vertebralis. Both the DDL and the DVL include the coccygeal myofascia and periosteum of the skull. Due to differences in biped and quadruped anatomy the Front Limb Adduction Line (FADL) and the Front Limb Abduction Line (FABL) differ from the human lines. The lines are identified as slings in the brachial and antebrachial regions. The FABL includes structures for abduction and internal rotation connecting to the Front Limb Retraction Line (FLRL), and the FADL structures of adduction and external rotation in close proximity to the Front Limb Protraction Line (FLPL). The front limb lines support the movement of the front limb around the “thoraco-scapula pivot joint” medially at the level of the upper third of the scapula. The DVL identified in this study is similar to the human DFL whereas the front limb lines differ somewhat from the deep human arm lines due to differences in bi- and quadruped anatomy and biomechanics. We have identified and described this new equine DDL. The lines altogether explain a profound body balance and confirm the three-dimensional equine fascial network, which is of great clinical and biomechanical importance.

Back pain is a common condition in horses, yet despite this, quantitative assessments of the efficacy of treatment are scarce. Mechanical nociceptive thresholds (MNTs) and acoustic myography (AMG) recordings were obtained, both preinterventionand postintervention, from the left and right epaxial muscles in eight healthy general riding horses (mean age 17 ± 6 yrs). Using an algometer, MNT readings were taken at each of the 6 preselected points along the thoracolumbar M. longissimus and M. gluteus medius region. AMG recordings of the M. longissimus and M. gluteus medius were taken while walking, trotting, and cantering on a left or right hand 20m circle on a longe, on a waxed sand surface in an indoor arena. Horses were then treated using a class 1 laser. Therapy was applied for 1 minute at 1000 Hz to the same preselected points from which MNT measurements had previously been taken. Measurements were subsequently taken 1 hour and 24 hours post-treatment for MNT reading, and only 24 hours after for AMG measurements. No significant effect of treatment was noted for the MNTs. The AMG results were analyzed in terms of their temporal summation (T-score), where statistically significant improvements in the T-scores for M. longissimus and M. gluteus medius were noted for the different gaits. It is concluded that cold laser therapy has a positive effect on horse muscles that reveals a change in their firing frequency that is commensurate with changes seen with analgesia in subjects experiencing pain.

The aim was to test the hypothesis that prenatal under‐ and overnutrition in late gestation can program small intestinal (SI) growth, angiogenesis, and endocrine function to predispose for a hyperabsorptive state, thereby increasing the susceptibility to the adverse effects of an early postnatal obesogenic diet. Twin‐pregnant ewes were exposed to adequate (NORM), LOW (50% of NORM), or HIGH (150% energy and 110% protein of NORM) diets through the last trimester (term ~147 days). From 3 days to 6 months of age, their lambs were fed either a moderate (CONV) or a high‐carbohydrate high‐fat (HCHF) diet. At 6 months of age, responses in plasma metabolites and insulin to refeeding after fasting were determined and then different segments of the SI were sampled at autopsy. Prenatal overnutrition impacts were most abundant in the duodenum where HIGH had increased villus amplification factor and lowered villi thickness with increased IRS‐1 and reduced GH‐R expressions. In jejunum, HIGH lambs had an increased expression of Lactate gene and amplified when exposed to HCHF postnatally. Specifically, in LOW, sensitivity to HCHF was affected in ileum. Thus, the mismatching LOW‐HCHF nutrition increased expressions of angiogenic genes (VEGF, VEGF‐R1, ANGPT1, RTK) and increased mucosa layer (tunica mucosa) thickness but reduced muscle layer (Tunica muscularis) thickness. The SI is a target of prenatal nutritional programming, where late gestation overnutrition increased and shifted digestive capacity for carbohydrates toward the jejunum, whereas late gestation undernutrition predisposed for ileal angiogenesis and carbohydrate and fat hyperabsorptive capacity upon subsequent exposure to postnatal obesogenic diet.

Badly designed and fitted tack induces physiological stress responses in horses, and may compromise animal welfare. Moreover, horses, just like humans, comprise a series of interconnected myofascial lines. However, to date there are no measurements of the effects of horse tack, such as bridles on muscle parameters. This study used acoustic myography to test whether two commercial anatomically designed and fitted bridles, have a measurable and positive effect on both equine muscle-function and performance. A Quantum bridle was tested on 12 Icelandic horses, whilst a Finesse bridle was tested on 8 Icelandic horses, and results compared with data from a standard bridle (n = 12) tested at the same time and under identical conditions. Sensors were placed on M. Brachiocephalicus and M. Splenius, and the horses exercised following a set protocol at three speeds. The results revealed statistically significant improvements in muscle performance as assessed by both the regularity of the recording at each speed, and the number of transient powerful contractions (spikes) for the anatomically designed and fitted bridles, compared with the standard bridle. It is concluded that the effect of anatomically designed bridles can not only be measured in the neck muscles of exercising horses, but that they appear to have a positive effect on muscle performance.

Fascia in the veterinary sciences is drawing attention, such that physiotherapists and animal practitioners are now applying techniques based on the concept of fascia studies in humans. A comprehensive study of fascia is therefore needed in animals to understand the arrangement of the fascial layers in an unguligrade horse and a digitigrade dog. This study has examined the difference between the horse and the dog fascia at specific regions, in terms of histology, and has compared it with the human model. Histological examinations show that in general the fascia tissue of the horse exhibits a tight and dense composition, while in the dog it is looser and has non-dense structure. Indeed, equine fascia appears to be different from both canine fascia and the human fascia model, whilst canine fascia is very comparable to the human model. Although regional variations were observed, the superficial fascia (fascia superficialis) in the horse was found to be trilaminar in the trunk, yet multilayered in the dog. Moreover, crimping of collagen fibers was more visible in the horse than the dog. Blood vessels and nerves were present in the loose areolar tissue of the superficial and the profound compartment of hypodermis. The deep fascia (fascia profunda) in the horse was thick and tightly attached to the underlying muscle, while in the dog the deep fascia was thin and loosely attached to underlying structures. Superficial and deep fascia fused in the extremities. In conclusion, gross dissection and histology have revealed species variations that are related to the absence or presence of the superficial adipose tissue, the retinacula cutis superficialis, the localization and amount of elastic fibers, as well as the ability to slide and glide between the different layers. Further research is now needed to understand in more detail whether these differences have an influence on the biomechanics, movements and proprioception of these animals.

Introduction: Socalled myodural bridges (MDB) linking the suboccipital muscles to the dura mater have been described in the human, canine, small ruminants, monkeys, rodents, porpoises, crocodiles, sperm whales, chickens and lately in equines. They are believed to have biomechanical functions and might also play a role in head/neck pathology and the pumping function of the cerebrospinal fluid. Up to now these bridges have only been described briefly in the horse in terms of their anatomy, and then only in relation to Ehlers-Danlos syndrome. The aim of this study was therefore to investigate and thoroughly describe the anatomy, biomechanics and integration of this complex throughout the equine spine, with special focus on the upper neck, the cervicothoracic- and the lumbosacral transitions. Pathology in these regions is well recognized in horses. Material and methods: Horses were dissected, the heads and spine prepared in several anatomical planes, the heads MR-scanned and histology performed on the AO and AA MDBs. Results: Gross anatomical observations showed that muscle-membrane-spinal dura mater connections (MDB) were evident in the full equine columna vertebralis, and were specifically developed in the upper cervical, the cervicothoracic and the lumbosacral transitions. In the upper cervical region, the m. rectus capitis minor and major and the m. obl. cap caudalis attached tightly to the dorsal intervertebral AO and AA membranes. On the ventral membrane surface there was a trabecular connection to dura mater. The two membranes differed markedly in the amount of elastic fibers giving them different biomechanical function. The structures of the AO MDB were evident on the MRI scans. Conclusions: Horses, like humans, other mammals, a reptile and a bird to date, have myodural bridges, which are tightly integrated with surrounding structures as well as the biomechanics of the upper neck. In addition, similar structures are present throughout the whole spine.

Introduction: The hypothesis of this study is that fascial anatomy provides new aspects in functional anatomy. M. biceps femoris and m. vastus lateralis are broad muscles, which participate in force transmission of the hindquarters. The aim of the study was to dissect fascial anatomy of the hind limb region in more detail than the present literature shows.

Introduction: Myofascial kinetic lines balance the body in motion and standing and are important tools when diagnosing locomotion dysfunctions. Thomas Myers defined 10 lines in humans (Myers 2014). In horses, seven of these lines were dissected and published (Elbrønd & Schultz 2015). Compared to human, the equine lines vary due to the difference in posture, biped versus quadruped. Three lines still need to be dissected and validated in horses: Two equine profound front limb lines, PFLL, and a deep ventral line (DVL). The three lines are important because they balance external versus internal. Based on clinical experiences an equine deep dorsal line (DDL) is missing in this balance. The purpose of this study was to dissect and validate the equine DVL, DFLL, and DDL.

This study aimed at looking at the frequency (T-score) and the amplitude (S-score) of fiber use during contraction of a forearm muscle, m. palmaris longus, as measured by acoustic myography (AMG). An additional aim was to relate the T-and S-scores to the recorded force obtained from a hand dynamometer. The hypothesis being that temporal and spatial summation of muscle fiber contraction in a given muscle during a given movement, can together describe a given obtained force. Force measurements were carried out on 12 healthy human subjects aged 19-68 years (6 men & 6 women), while their m. palmaris longus contractile function was measured using an acoustic myography CURO device. Force production was varied from 90 to 10% of assessed maximal voluntary force (MVF), and also monitored over a 1 min period of 50% MVF. Linear regression analysis was applied to relate force to spatial and temporal summation. Muscle strength was sustained by changing the frequency and/or the number of active fibere at any given point in time. Force production, whilst stronger for men than women, was regulated in a similar fashion for both sexes and was closely correlated with the AMG T-and S-scores. It is concluded that AMG is a noninvasive method which can be readily applied to accurately describe how a subject uses a given muscle during any given movement. These findings have relevance when considering training strategies in subjects with muscle trauma or disease, in the elderly, or for both amateur and top professional athletes.

Introduction: Whilst fascia research continues to interest the field of veterinary medicine, there remains a dearth of information about differences in both the macro and micro anatomical structures of fascia in diverse species of animals. The aim of this study, therefore, is to compare the fascia of the horse and the dog in three specific regions at the microscopic level.

It has been proposed that manipulating proprioceptive signals of the equine distal limb as part of a rehabilitation process in cases of musculoskeletal pain or neurologic deficits can be used to correct postural control and restore normal motor programs. This trial has examined the effect of treatment with a light-weight and loose-fitting bell boot (82 g) on an imbalance of muscle gluteus superficialis function in horses as measured using acoustic myography (AMG). Eight horses were trained over a 60-minute period every 3 days for 6 weeks, a protocol based on preliminary findings. Acoustic myography measurements, recording the coordination, spatial and temporal summation of muscle contractions, were made at the start (baseline) and at the finish (week 6) after a warmup period and following a set procedure of physical activity. Walking, trotting, and cantering during a left-hand circle at the start of the trial revealed a slight but significant asymmetry between the left and right hind limb muscle, which improved successfully after 6 weeks of proprioception training. Data for the right-hand circle, which revealed no significant asymmetry, during walk, trot, and canter at the start, showed no change after 6 weeks of training at the walk and trot but developed an imbalance during cantering, the result of overcompensation. This study demonstrates that functional musculoskeletal asymmetry measured during periods of activity can not only be accurately detected using AMG but it also reveals an association between the program of proprioceptive training adopted and an improvement in muscular imbalance.

This review documents some new advances in the field of Veterinary medicine with specific focus on the exciting research area of myo-fascia. It presents some of the latest findings in structure as well as function of these interconnected tissues, as well as highlighting the effects and benefits of treatment for such underlying issues as regional stiffness affecting performance, and the role of myofascial kinetic lines. It likewise addresses some of the new and non-invasive techniques such as accelerometry, multi-frequency bioimpedance and acoustic myography that have emerged over recent years, and illustrates how they can be readily adopted in the Veterinary clinic to assess muscle imbalance and injury as well as to direct such treatment as myofascial release therapy, acupuncture and proprioception and to follow rehabilitation. impaired cellular energy storage, respectively. The data collected using a small accelerometer detected a change in gait in this horse that was found to disappear after a local anaesthetic was applied to the region identified by x-ray as being the worst “Kissing spine” lesion (Harrison et al 2018). These authors concluded that acoustic myography, bioimpedance and accelerometry in combination may provide a useful set of diagnostic data that could potentially assist in not only rapidly determining the site and extent of muscular injury but quite possibly in directing treatment and rehabilitation in afflicted horses.

Introduction: The hypothesis of this study was that peripheral nerves, which are attached to fascial sheets, are affected by the movement and tension of the fascia. Detailed macro- and microscopical studies were performed to validate the structural and functional connections between peripheral nerves and fascia.

Equine Myodural Bridge, a novel discovery – gross anatomy, histology and in vitro MRI Vibeke S. Elbrønd, Ass. Prof. Anatomy, Ph. D, IVH, Faculty of Health & Medical Sciences, Copenhagen University, Denmark, vse@sund.ku.dk Rikke M Schultz, DVM, RMS Equine Practice, Karlebovej 22, 2980 Kokkedal, Denmark, rms@rikkeschultz.dk Background The myodural bridge (MDB) is defined as the indirect fascial contact between m. rectus capitis minor (RCM), the atlanto-occipital membrane (MAO) and the dura mater (DM). In human it has been known for some decades [1;2], but it has never been identified in horses [3]. The last years of research has focused on the function of the MDB in relation to symptoms such as chronic headache, dizziness, nausea, imbalance, vision dysfunctions and loss of memory [4]. As horses are prone to head and neck trauma and different riding techniques, they are frequently presented in the clinic with chronic biomechanical neck dysfunctions. This study was undertaken to investigate if an equine MDB was present. Methods Ten horses of different breeds and gender were euthanized due to other reasons than the studies. The horses were treated with respect to animal welfare. Head and neck were meticulously dissected, frozen and cut in transverse and sagittal planes or MRI-scanned with head and neck in flexion and extension. Additionally, histological samples were collected from the MDB. Results The gross dissections showed obvious contact from RCM through the dorsal membrana atlanto-occipitalis to DM in the atlanto-occipital (AO) space. Additionally, in the dorsal intervertebral atlanto-axial (AA) space myodural contact was seen to m.obl. cap.caudalis and lig. nuchae via membrana atlanto-axiale (MAA). The two membranes also had close connections to the respective joint capsules of the facet joints. Histology showed the membranes to have three layers with variation in density and direction of collagen fibers and hyaluronan content. Several retinacular structures were observed between the membranes and the DM. Movement of DM was visible when stretching the muscles manually. On MR images of cadaver necks the MDB’s were obvious.

Knowledge of the anatomy and topography of the equine back are essential for a correct diagnosis and treatment as well as communication among therapists, especially since different authors have not always agreed upon the anatomical topography of the epaxial back muscles.In this study, we performed a novel 3-D dissection procedure that focused on maintaining the integrity of the myofascial role in muscle topography.A total of 17 horses were carefully dissected, recorded and videotaped.The results revealed some interesting points.1) The iliocostalis muscle (IL) was found to be clearly distinct from the longissimus dorsi muscle (LD) and positioned ventral to the lateral edge of LD. 2) Two distinct variations in the origin of the IL, i) from the Bogorozky tendon and the ventral epimysium of m. longissimus dorsi (LD) at the caudo-lateral region at L1 to L5, and ii) from the lumbar myofascia lateral to the lumbar transverse processes at the level of L2 to L4 have been found.3) A fold in the LD from the thoracolumbar junction to the cervicothoracic junction was identified.It is concluded that: i) the IL muscle is the smallest of the 3 muscles in the erector spinae group with variations in the origo; ii) the LD fold may play a stabilizing role and the lateral section of the LD may act bilaterally in extension and unilaterally in lateral flexion; iii) the m.spinalis (SP), incorrectly labelled in previous studies, may be related to extension only in the cervicothoracic region, whilst the LD may be primarily responsible for extension in the thoracolumbar region.