Equine field practice commonly requires short- to medium-term anesthesia being induced in horses for either minor surgical or diagnostic procedures or for urgent medical care in emergency situations. Performing a general anesthetic in the field further increases the risk associated with equine anesthesia which already is high when compared with small animal or human anesthesia, even under best of hospital conditions. For this reason, cases for field anesthesia should be carefully selected and appropriate anesthesia protocols chosen by taking into account the peculiar setting of the location, the physical condition of the patient, and the specific circumstances of the surgical, diagnostic, or other procedures planned. This review provides an overview of the anesthetic techniques suitable for field anesthesia. First, the approach to the equine patient under field as compared with hospital conditions is addressed, followed by a detailed discussion of common field anesthetic protocols reported for use in adult horses and in foals. Finally, anesthetic protocols suitable for horses suffering injuries during or immediately after maximum exercise are addressed.
Vascular disorders play an important role in male infertility. Various modalities of ultrasound examination can be applied to evaluate testicular vasculature and to objectively measure numerous parameters of testicular perfusion. This paper describes techniques of ultrasound examination of testicular vasculature in the stallion, using gray-scale, color, and power Doppler ultrasound. Results of studies on the normal vascular anatomy in the stallion and its variations, the methods of obtaining most optimal measures of testicular perfusion, and the effects of the physiological and pharmacological factors on testicular blood flow are reviewed. There is a growing body of evidence that evaluation of testicular vasculature has a tremendous clinical relevance and should be included in the diagnostic workup of scrotal diseases.
Magnetic resonance (MR) imaging is the gold-standard imaging modality for diagnosing tendon and ligament pathology. MR is capable of detecting lesions that are not visible with other imaging modalities. Pathologic changes in tendons and ligaments are seen on MR as changes in size, shape, and/or signal intensity of the affected structure. All tendons and ligaments have individual characteristics and variations in normal appearance. This chapter describes the normal MR appearance of the tendons and ligaments of the distal limb, as well as discussing the ways in which damage to individual tendons and ligaments affects how they appear on MR images.
A variety of surgical procedures are available to ameliorate the discomfort of tendonitis or desmitis, treat the original cause, or enhance healing. The following current techniques are described: neurectomy of the deep penetrating branch of the lateral plantar nerve, suspensory ligament fasciotomy, desmotomy of the palmar/plantar annular ligament via an extrasynovial approach and using arthroscopic guidance, desmotomy of the accessory ligament of the superficial digital flexor tendon (AL-SDFT, proximal check ligament) via the direct medial approach and via arthroscopic guidance, and desmotomy of the accessory ligament of the deep digital flexor tendon (AL-DDFT, distal check ligament).
Pain is a subjective and complex multidimensional sensory experience that usually occurs as a result of tissue trauma. It is generated after extensive neuronal signal processing within the brain following the activation of peripheral high-threshold sensory receptors (nociceptors), which send nerve impulses from the periphery to the central nervous system. Pain resulting from stimulation of nociceptors can be considered a physiological phenomenon as it helps minimizing further tissue damage by activating reflex withdrawal mechanisms and increasing behavioral, autonomical, and neurohumeral responses that are aimed at maintaining body integrity, preventing further tissue injury and promoting healing. However, if persistent, mechanisms described as peripheral and/or central sensitization alter the pain experience in the patient, transforming physiological pain into maladaptive pain, which is dissociated from the original noxious stimuli or healing process. Thus, maladaptive pain must be considered a pathological condition in and of itself. It is often responsible for persistent discomfort and stress of the horse, which can lead to abnormal behaviors, reduced quality of life and, if uncontrolled, distress and eventually humane destruction of the animal. This article intends to give an overview of the anatomic sides as well as physiological and pathophysiological processes involved in the generation, conduction, and integration of nociceptive signals and presents a pain classification scheme that is more indicative of the neural mechanisms underlying pain phenomena and thus provides the veterinarian with a better direction of how to approach pain therapeutically.
Managing pain effectively is one of the most important tasks that clinical veterinarians perform on a daily basis. This requires accurate assessing and grading of perioperative or posttraumatic pain followed by effective treatment. Commonly, veterinarians rely on the interpretation of physiological indices such as heart and respiratory rates, and, in case of musculoskeletal pain, on lameness evaluation. However, accurate assessment of pain in horses is complicated, not only because there are as many types of pain as there are responses to injuries, but also because criteria used to assess pain are often confounded by other factors. More recent studies suggest that subjective and objective assessment of species-specific pain behaviors should become an integral part of pain evaluation also in the horse, and that physiological and behavioral data combined are more useful than physiological measures alone to assess pain and the response to treatment in an individual animal. Pain scoring systems have recently been adapted to the horse and may prove useful in judging progress and response to treatment during the perioperative period. Effective pain therapy is best accomplished by applying a multi-modal or balanced analgesia concept that involves the combination of drugs with different pharmacological mechanisms of action and different target sites within the nociceptive system. Balanced analgesia may also include complementary modalities of pain treatment, such as acupuncture or chiropractic manipulations, especially when dealing with conditions of chronic pain.
Magnetic resonance (MR) imaging provides the opportunity to evaluate structures within the limbs and head that were previously unable to be visualized in live horses. MR imaging has also enabled osseous and soft tissue structures, visible with radiography and ultrasonography, to be evaluated in greater anatomic and physiologic detail. For MR imaging to provide the most accurate and useful information in horses, it is important that the examinations be standardized. It is also important that collection of the images be performed in the most time-efficient manner. This chapter outlines the imaging planes and sequence selection that are most useful when imaging the limbs and head of the horse using a 1.0 Tesla superconducting magnet with the horse under general anesthesia. With this system, imaging of the head, cranial cervical vertebrae, feet, pasterns, fetlocks, metacarpal and metatarsal regions, carpi, and tarsi is possible in the adult horse. In foals and miniature horses, it is possible to image more proximally on the limbs and more caudally in the cervical vertebrae.
Of the two flexor tendons in horses’ lower limbs, the superficial digital flexor tendon is more commonly injured than the deep digital flexor tendon. Flexor tendon injuries are caused by either overstrain of the tendon or direct trauma. Overstrain injuries have a typical swelling of the tendon that requires ultrasonographic evaluation to confirm the diagnosis. Treatment of these injuries includes anti-inflammatory therapy initially followed by a rehabilitation program. New therapies are emerging for modulating healing of these injuries. Flexor tendon lacerations are usually the result of direct penetrating trauma to the limb. Management of these injuries includes surgical management combined with appropriate coaptation. Involvement of a tendon sheath complicates management with the potential formation of septic tenosynovitis. The prognosis for returning successfully to athletic function in the case of overstrain injuries is fair, but re-injury is common, and for tendon lacerations, it is guarded to poor.
The following article aims at giving an overview on currently available balanced anesthetic regimens for horses. In horses, maintenance of cardiovascular function and thus muscular perfusion during anesthesia is essential. Also, a smooth recovery phase which should be completed within at least 1 hour of termination of drug administration is crucial. All inhalation anesthetics depress cardiovascular function dose dependently. Thus, drugs that decrease the need for inhalation anesthetics (decrease MAC) might improve cardiovascular function during anesthesia. Lidocaine constant rate infusion (CRI), at clinically used dose rates, decreases MAC by about 25%, and no untoward cardiovascular side effects have been reported. In horses anesthetized for several hours, careful dosing is advised. Toxicity due to accumulation, masked during anesthesia, might become apparent during recovery. Ketamine is the only drug used for balanced anesthesia that might positively influence cardiovascular function. But following continuous ketamine administration for longer time periods (>2 hours), rough recoveries can occur. Preliminary results with S-ketamine CRIs showed better results in this respect, but further studies are warranted. Medetomidine CRI does decrease MAC about 30% at recommended dose rates. Cardiovascular function in comparison to lidocaine balance is moderately impaired, but horses show less intraoperative awakening following surgical stimulation. Recovery phase following medetomidine balance is clearly smoother than with any other regimen. In conclusion, lidocaine, ketamine, and medetomidine are mainly used for balanced anesthesia in horses. In cardiovascularly compromised patients, ketamine might be advantageous. If a smooth recovery phase is crucial, medetomidine should be the drug of choice.
Assessment and management of an enlarged scrotum in the stallion presents a diagnostic and therapeutic challenge. Depending on the etiology and severity of the enlargement, irreversible injury may result to the reproductive system and adjacent structures. Although appearing clinically similar, scrotal enlargements vary widely in their cause. Interventions should be aimed at evaluation of the structures involved, with assessment of the degree of tissue compromise followed by timely and rational medical and surgical therapies.
Horse owners worldwide now request that their mares be bred with cooled or frozen-thawed transported semen, owing to the advantages of avoiding mare transport (often with a foal by her side), decreasing disease transmission between farms, and most importantly, the accessibility to a wider genetic pool. This has become commonplace practice as many breed registries now allow the use of transported semen for producing foals worthy of registration. However, problems arise as optimal steps for both semen handling and preparation, as well as for mare breeding management, are not practiced. Therefore, the objective of this manuscript is to provide veterinary practitioners with an overview about optimal management techniques related to both handling semen and mare management for attaining successful results. Common problems and dilemmas encountered will be also discussed and emerging research introduced. Whereas appropriate protocols for handling and preparing semen for cooled-transport will be presented with some detail, it is beyond the scope of this paper to discuss stallion semen cryopreservation, which typically requires extensive equipment investment and expertise and is usually done at referral and specialized centers. This text assumes that the equine veterinary practitioner already has some basic skills in regards to stallion semen collection and evaluation, as well as in performing examination of the mare via transrectal palpation and ultrasonography for breeding management purposes.
Magnetic resonance imaging has revolutionized the diagnosis of foot-related pain, defining many soft tissue injuries that had previously been poorly recognized and greatly enhancing our understanding of pathological abnormalities of the navicular bone. The concept of multiple injuries contributing to lameness has been recognized. It has become clear that lesions may predate the onset of lameness. A better understanding of pain causing lameness is required.
A wide variety of infectious bacterial, viral, and protozoal reproductive pathogens have the potential to be transmitted by the breeding stallion. In addition, nonvenereal diseases can also be spread due to the close proximity of mares and stallions during natural service. Disease spread by assisted breeding techniques is also possible. The equine veterinarian must develop a thorough understanding of the relevant diseases and be able to formulate treatment and management plans to minimize the effects of infection on breeding programs.
As use of magnetic resonance (MR) imaging evolves in veterinary medicine, the importance of field strength will be a continued source of debate. This article addresses the fundamental differences between high- and low-field MR imaging systems. The magnet and room construction, examination time, image quality, and implications on diagnostic accuracy are discussed. Although many injuries can be well characterized with both high- and low-field systems, a high-field system is required to identify certain lesions. Further studies are needed to define the difference in the detectability of lesions on high-field versus low-field MR imaging systems.
Testicular degeneration is a common cause of subfertility and infertility in stallions. The disease can broadly be divided into two categories: those cases resulting from a known testicular insult, and idiopathic (senile or age-related) testicular degeneration. This manuscript describes the problem of testicular degeneration in the equine breeding industry and summarizes what is known about the pathophysiology of the disease. Additionally, the clinical signs of testicular degeneration are reviewed so that the clinician can more quickly and accurately arrive at a diagnosis. Differences in the approach to treatment of testicular degeneration arising from a known cause and idiopathic testicular degeneration are discussed as are differences in prognoses. Finally, the practitioner is provided with practical information on how to more effectively manage affected stallions and what, if anything, can be done to improve reproductive performance of these animals both in the field and in a referral setting.
Suspensory injuries involving either the proximal one-third or the branches are potentially career-ending injuries for sports horses. Injuries can occur alone or in conjunction with their osseous attachments, and this may influence the prognosis. Clinical presentations can be hugely variable, and this paper discusses in depth the recognition of such injuries, ancillary diagnostic techniques, and management.
Magnetic resonance (MR) imaging is a complex modality that produces vast amounts of information. This information is shown as gray scale contrast derived from variations in signal intensity. Normal tissues have characteristic signal intensity patterns and contours. Alterations in tissue biochemical composition, structure, shape, and size can be detected using MR imaging and are seen as alterations in signal intensity and contour of the anatomical structures being evaluated. However, the appearance of MR images are affected greatly by the pulse sequences used in acquisition, the imaging options, and positioning of the region of interest. MR imaging is also prone to a variety of artifacts. It is therefore important that the interpreter has an understanding of the limitations of MR imaging and how best to optimize and interpret the information collected. It is also important that this information is interpreted in the light of the clinical findings and other diagnostic information for each horse.
To have confidence in magnetic resonance (MR) imaging as a diagnostic tool for evaluation of the equine limb, validation of the procedures involved in image acquisition and interpretation is required. It is also important to understand the benefits and limitations of MR imaging by comparison with the macroscopic and microscopic structural abnormalities present within the tissues. This paper outlines various validation procedures that we have undertaken for image acquisition, image interpretation and measurement of structures, and comparison between MR images, macroscopic and histological examination of the equine foot, tarsal, and carpal tissues.
Pain management in the equine relies predominantly on systemic or local/regional drug therapy. Nonsteroidal antiinflammatory drugs, opioids, alpha 2 -adrenoceptor agonists, and local anesthetics are the chief agents employed in equine pain therapy. This review briefly discusses the principle pharmacology of the analgesic drug classes currently in use in equine practice, and then focuses on recently introduced therapeutics and/or new routes of drug administration. General guidelines and dosages are given to assist in choosing appropriate drugs and techniques that provide effective analgesia.
In human and animal anesthesia, epidural and spinal administration of drugs is used to provide surgical anesthesia and/or postoperative analgesia. Several local anesthetic drugs are used to produce epidural anesthesia, such as lidocaine, bupivacaine, ropivacaine, and mepivacaine. Epidural analgesia is obtained with opioid agonists, alpha2-adrenergic agonists, and ketamine. In horses, caudal epidural anesthesia is used to desensitize the anus, rectum, perineum, vulva, vagina, urethra, and bladder. The goal is to produce surgical regional anesthesia without losing motor function of the hind limbs. A combination of a local anesthetic drug with an alpha2-adrenergic agonist or an opioid is the most popular option as this combination extends the period of action of the epidural anesthesia or analgesia in horses, humans, and small animals. Spinal analgesia and anesthesia has not been used in horses as an adjunct to general anesthesia as much as it has in small animals and human beings. The epidural administration of opioids with or without local anesthetics is commonly performed in dogs and cats before surgery to reduce general anesthetic requirements as well as to provide intraoperative and postoperative pain control. The perioperative use of epidural and spinal analgesia in horses is likely to increase in the future as recent studies have shown that administration of epidural or subarachnoid alpha2-adrenergic agonists, phencyclidines, opioids, and low-dose local anesthetic produce intense antinociceptive effects.
