Veterinary Education Abroad
The American Association of Equine Practitioners (AAEP) hosts the largest continuing education seminar in the world for horse vets at their annual convention. They also host several other conferences and wet labs. Each year AAEP picks a destination for a "resort" symposium in late January before the racing and breeding seasons become unmanageable. This year for the eighth resort symposium, they selected Rome, Italy. This merged nicely with the World Equine Veterinary Association (WEVA) biennial meeting, which this year was held in Marrakech, Morocco, a short plane trip from Rome.
WEVA is a not-for-profit educational group that tries to bring world-class veterinary continuing education to parts of the world that might not otherwise have access to some of the key speakers and researchers found at other seminars. This is the ninth convention for WEVA.
Following is some of the information presented from the three-day AAEP meeting and the five-day WEVA meeting. Proceedings of these seminars can be obtained from the host organizations (www.AAEP.org and www.weva2006.ma).
Peter Daels, DVM, PhD, Dipl. ACT, ECAR, of the Equine Embryo Transfer Center KEROS in Belgium, discussed "Induction of Lactation and Adoption of the Orphan Foal" during the AAEP symposium.
A few years ago, a procedure was introduced by Daels that allows a barren mare to be stimulated with hormones and start producing milk for an orphan foal. Daels updated his procedure, and now can have a mare producing substantial quantities of milk within a week to 10 days.
The treatment includes estrogen, progesterone, and a dopamine D2 antagonist (sulpiride or domperidone). It is used on mares that at least once have successfully given birth and nursed a foal. After about four to seven days, the mare should be milked five to seven times a day. After three to four days of milking, production should have reached three to five liters of milk per day. At that point, Daels said, the mare is ready to adopt a foal.
Mares are placed behind a metal pipe that keeps them from turning. During the introduction period, the foal is held close to the mare's head while the mare receives vaginal-cervical stimulation (a vigorous massage of the external portion of the cervix and some attempt to dilate the cervix). The stimulation is applied twice for three minutes at 10-minute intervals. The mare is allowed to sniff and lick the back and buttocks of the foal during and after the procedure.
Daels said adoption took significantly longer for mares that did not receive the vaginal-cervical stimulation than for mares that did. He reported that using the cervical massage method (and under experimental conditions), 14 of 16 mares adopted the foal immediately and maternal behavior developed completely and immediately following the cervical massage. In mares not undergoing vaginal-cervical stimulation, only two adopted immediately and the remaining 14 mares displayed aggressive and potentially harmful action toward the foals from four to 24 hours.
Foals were supplemented with artificial milk three to five times per day (one to two liters each feeding) until the foals refused the artificial milk or when it was judged the mare was producing sufficient milk.
The Upper Airway
"Why worry about the airway?" queried Susan J. Holcombe, VMD, PhD, Dipl. ACVS, ACVECC, of Michigan State University, at the AAEP symposium. "Because the oxygen goes from the air to the muscles to fuel them."
The numbers back up the importance of an airway that is functioning normally for the performance horse: At rest, the horse breathes about 12 times per minute, with a tidal volume of about five liters, at an airflow of five liters per second. During intense exercise, the horse breathes about 120 times per minute, with a tidal volume of 12-15 liters, at an airflow of 75 liters per second.
The real issue, said Holcombe, is that when people hit a certain exercise intensity, they start oral (mouth) breathing to increase airflow and volume. A horse can't do that because of the placement of the epiglottis. Some horses with dorsal displacement of the soft palate (DDSP) will attempt to mouth breathe, but that is rare.
"Racehorses are eliminated by their respiratory systems," Holcombe said.
Holcombe discussed in detail the structures, muscles, and nerves associated with airway function and what could go wrong. At one point she asked if we could attempt to dilate or expand the airways to allow horses to breathe easier. Some of the tack modifications used include tongue-ties.
Holcombe said one study compared the position of the hyoid apparatus (a key support structure of the nasopharynx) with and without the tongue tie in the anesthetized and exercising horse. The tongue tie did not work in either case. However, she said, the problem with this study might have been that researchers used normal horses, not those that needed the extra air space.
She also noted that manual traction on the tongue (such as with a tongue tie) differs from active contraction of the genioglossus muscle that is responsible for pulling the tongue down flat and allowing it to protrude from the mouth.
"Depression of the tongue may be the critical action of the genioglossus and hyoglossus muscles in stabilizing the upper airway," she noted.
Research in Great Britain on horses with DDSP found no difference in horses with or without a tongue tie. In fact, Holcombe reported, some horses that didn't displace before a tongue tie was used did displace after a tongue tie was applied.
"It might be effective on the right horses, but how do you select the right horses?" she queried.
She said researchers still don't know what causes DDSP. "We can create the disease in a number of ways," she noted. "And multiple treatments usually mean multiple causes."
She said the best way to diagnose DDSP is on a treadmill because some horses displace a low speeds, some only at high speeds, and some after high-speed work while slowing down. Also, Holcombe added, horses will displace at different phases of respiratory cycle, and some displace when they swallow. Some displace when exhaling, and some when inhaling.
"A disease that happens at so many different phases of exercise and respiratory phase, probably the causes are not alike," she concluded.
A question from the audience asked if there is a consistent pattern of displacement in the same horse. "Yes," she replied, "once we know how to get a horse to displace. Some have to have full tack. Some have their head tied down. Some when they slow down. Once we find out, we can get them to displace at the same time again. Fatigue might be a component to this because once we get them to displace, they will do so over and over."
Holcombe then posed the questions: How do we diagnose respiratory problems, and how do we fix them?
Horses make "noise" during breathing for many reasons, including DDSP and laryngeal hemiplegia. The latter occurs when the vocal cord and arytenoid cartilage collapse into the airway during inspiration, increasing resistance to airflow.
The problem with treating laryngeal hemiplegia, noted Holcombe, is that the arytenoid cartilage must fully abduct (the larynx must be fully dilated) during strenuous exercise and fully adducted (larynx must fully close) during swallowing.
There are several procedures to treat this problem, noted Holcombe. The complaint (exercise intolerance, noise production, or both) usually dictates the type of surgery used. She reviewed several studies and concluded that based on airway mechanics and blood gas values (amount of oxygen the horse uses), laryngoplasty (tie-back surgery) makes exercise performance better, but does not make the horse normal.
She reminded the audience that sound analysis is important since the U.S. Equestrian Federation (regulating body for U.S. equine sport) says horses cannot make noise upon exercise.
So, her conclusion based on multiple studies and personal experience is to remove the ventricles to treat noise associated with laryngeal hemiplegia, remove the vocal fold to prevent collapse into the airway, and use laryngoplasty to improve airway function.
For DDSP, Holcombe said there are more procedures and less successful treatments. She says these horses often have exercise intolerance associated with a gurgling, expiratory (during exhale) noise, which is found in 70-75% of horses diagnosed with DDSP. However, not all horses with DDSP make noise.
"Some horses displace at rest and not at exercise, and vice versa," said Holcombe.
Treatments include using a tongue tie, corticosteroids, changing tack, surgical tie-forward, and using laser surgery to firm up the soft palate. She said surgery is not recommended in young horses (2-year-olds); sometimes leaving them to mature cures the problem.
There were 500 veterinarians from 47 countries at WEVA. The host country provides much of the logistical and financial backing for the conference. His Majesty King Mohamed VI, King of Morocco, granted his patronage to the seminar.
WEVA holds meetings every other year with interim meetings--held between the regular ones--having taken place in Moscow, Kiev, Beijing, India, and Hungary. Des Leadon, MA, MVB, FRCVS, RCVS, head of clinical pathology and clinical services at the Irish Equine Centre and former WEVA president, said he was borrowing from the late John F. Kennedy when he suggested that veterinarians and researchers should think less of what WEVA can do for them, and more of what they can do for their colleagues.
The WEVA president for this conference was Mohammed Bakkoury, DVM, of Morocco. The incoming president of WEVA is former AAEP president Gary Norwood, DVM, of Louisiana.
Sue Dyson, VetMB, PhD, FRCVS, head of clinical orthopedics at the Animal Health Trust in Newmarket, England, spoke on "Proximal Suspensory Desmitis in the Hind Limb" at WEVA.
While this problem is recognized as being more common than previously thought in the hind limb, said Dyson, diagnosis can be difficult, and successful treatment can be challenging.
The principal function of the suspensory ligament is to prevent excessive extension of the fetlock joint, noted Dyson. Theonset of desmitis can be slow or sudden, mild to severe, unilateral or bilateral. She said some horses present with poor performance rather than lameness. Complaints include loss of hind limb impulsion, unwillingness to go forward freely, stiffness, resistant behavior, lack of power when jumping, refusing jumps uncharacteristically, difficulty in performing specific dressage movements (i.e., canter pirouette), poor performance at high speed in racehorses, and evasive behavior such as bolting.
"It is likely some lesions exist subclinically (without symptoms) or are associated with a low-grade lameness that goes unrecognized," said Dyson.
She noted that proximal suspensory desmitis in the hind limb occurs in horses performing all athletic disciplines and of all ages. "It is a particular problem in dressage horses working at advanced level," she said. "Horses with either straight hock conformation, and/or hyperextension of the metatarsophalangeal (hind fetlock) joint, appear predisposed to injury.
She stressed the importance of a good history and clinical signs with response to local analgesic techniques. When the proper area is blocked to look for proximal suspensory desmitis, Dyson said, in an ideal world you would see 100% improvement, but she looks for about 80% improvement. "Less than that and I look for something else," she said.
Ultrasound is important as a diagnostic tool, but it can be difficult to view that area. "The shape of the leg can make it difficult," she said. "You can have a negative ultrasound and still have proximal suspensory desmitis."
She said a thickened, tight fascia (covering on the tendon) can contribute to a compartment syndrome that is similar to achilles tendon pain in people. She said she also sees degenerative changes without active inflammation. "I've seen new bone formation distal to the ligament insertion (into the bone)," said Dyson.
Nuclear scintigraphy is not needed for most of these cases, opined Dyson. "In fact, if I have a high hind limb lameness that's negative on the scan, then I think suspensory desmitis," she said.
Treatment depends on time constraints, athletic expectations, rules for medication control during competition, degree of lameness and architectural disruption of the suspensory ligament, conformation, chronicity of the lesion, age of the horse, and the number of limbs affected, noted Dyson. She said the prognosis for proximal suspensory desmitis in the hind limb "has generally been poor. Only six of 42 horses seen in a referral practice were able to resume full work without detectable lameness for at least one year, all of which had been lame for less than five weeks. All these horses showed marked improvement in clinical signs within three months of the onset of lameness. Two additional horses resumed full work, but suffered lameness in another limb. Seven horses improved markedly and were able to work despite persistent mild lameness; 24 horses had persistent or recurrent lameness."
She said horses with acute (less than six weeks duration) hind limb proximal suspensory desmitis responded "reasonably well" to local infiltration with cordicosteroids. Foot imbalances should be corrected, and egg bar shoes are used to reduce extension of the fetlock. Stall rest usually doesn't help proximal suspensory desmitis in the hind limb.
Dyson noted that extracorporeal shock wave or radial pressure wave therapy seemed to help some cases. Tibial neurectomys were performed in eight horses, of which six returned to full athletic function (show jumping and horse trials) for at least two years after surgery. Neurectomy of the deep branch of the lateral plantar nerve combined with incising the thin plantar fascia was successful in 80% of more than 100 horses. "This is now my long-term treatment of choice," she said.
Back and Pelvis Injuries
While it has been known for centuries that horses have back pain, the technology to accurately diagnose the cause of primary or secondary back pain has only come about in recent years. Jean-Marie Denoix, DVM, PhD, of Centre d'Imagerie et de Recherche sur les Affections Locomotrices Equines (CIRALE) in Goustranville, France, one of the world's leading imaging experts, gave a talk at WEVA on "Diagnostic Imaging Back and Pelvis Injuries in Horses."
"In the last 15 years substantial improvement in the radiographic and ultrasonographic evaluation of the thoracolumbar and pelvic areas has been gained, allowing identification of lesions that were not accessible--or even imagined--before," said Denoix. "More recently, the use of nuclear scintigraphy has added new diagnostic information allowing a better assessment of the sensitivity and specificity of clinical and other imaging procedures."
Denoix stressed doing physical and dynamic (movement) exams on the back.
"The back is a large area with big muscles and low intravertebral mobility, so a dynamic exam is difficult," he noted.
His discussion of abnormal findings and lesions began with kissing spines (remodeling between two spinous processes), which have four grades:
- Narrowing of the interspinal space;
- Densification of the margins;
- Bone lysis adjacent to the margins; and
- Severe bone remodeling. He said the most common area for kissing spines are between T10 and T18, although they are not rare between L1 and L6.
"The frequency of kissing spines seem to vary according to the horse's discipline and biomechanical sollicitations of the back in specific gaits and exercises," noted Denoix. Generally speaking, he added, the lesions are commonly found in racing Thoroughbreds, and they seem to be well-tolerated in most cases. Intermediate frequency is observed in sport horses. They can be found in performance and sport horses without back pain. Kissing spines are not only a bony problem, said Denoix, but can involve the intraspinous ligament, so they can be treated with shock wave.
Injuries of the supraspinal ligament (SSL) alone are quite rare, and when found, usually are located in the cranial lumbar region. Denoix said osteoarthrosis of the articular facets (between spinous processes and vertebral bodies) is the most significant condition inducing back pain in horses (see figure on page 56). Diagnosis requires a powerful X ray machine. Therefore, absence of kissing spines does not rule out every osteoarticular cause of back pain.
Denoix said pelvic trauma is common in horses, although not always easily diagnosed. Powerful X ray machines can be used to image some of the structures on the standing horse or when the horse is under general anesthesia. Transrectal ultrasound has considerably improved the diagnosis of traumatic and degenerative problems. Nuclear scintigraphy is used to evaluate bone pathology in this area.
The lumbosacral junction can be a site of several problems that can be identified using ultrasound, he noted. Those include congenital abnormalities such as ankylosis (when bone fuses to bone), degenerative disc lesions (especially on the lumbosacral disc; see figure on page 56); intervertebral malalignment of the lumbosacral joint or the joint between L5 and L6; intertransverse lumbosacral osteoarthrosis (remodeling in the joint margins).
Denoix reminded the audience these tools can and should be used to follow treatments and verify healing.
EHV Neurologic Disease
Laurent Couetil, DVM, Dipl. ACVIM, associate professor of large animal/equine sports medicine, School of Veterinary Medicine, Purdue University, gave a talk at WEVA on "Equine Herpesvirus and Neurologic Disease."
Equine herpesvirus-1 (EHV-1) and -4 (EHV-4) are members of the Alphaherpesvirinae subfamily, genus Varicellovirus. The major illness associated with EHV-1 is abortion, and EHV-4 is known for causing respiratory disease in young horses. In addition, EHV-1 can cause respiratory disease, neonatal mortality, and neurologic disease. In rare cases EHV-4 can also cause abortion, neonatal disease, and neurologic disease.
Couetil noted that most horses over two years of age (80-90%) have detectable antibody titers to EHV-4, but seroprevalence for EHV-1 is lower (30-40%). He also said up to 50% of herpesvirus-1 infected horses become latent carriers for life, "therefore constituting a large reservoir of horses potentially shedding EHV-1." He said latent infections explain why some outbreaks of EHV-1 infection occur in closed herds in the absence of exposure to new horses.
"A susceptible horse may become infected because of exposure to respiratory secretions from an actively infected horse or to a fetus or fetal membranes aborted from a mare," he explained. "Alternatively, stress episodes or corticosteroid treatments may reactivate the virus in latently infected horses and result in EHV-1 infection."
EHV-1 can remain infective in the environment for up to 14 days, and on a horse's hair coat for up to 42 days, noted Couetil. Infected horses can shed EHV-1 virus in nasal secretions for up to 14 days.
The route of entry for EHV-1 is the upper respiratory mucosa via direct contact or by inhalation of aerosolized secretions containing virus. The incubation period for the neurologic form of EHV-1 is six to 10 days; horses that suffered prior infection are at higher risk of developing neurologic signs as compared to naive horses.
Morbidity (illness) rate varies from a singe case on a farm to up to 90% of exposed horses. Mortality (death) rate ranges from 0.5% to 40% of in-contact horses. Outbreaks of EHV-1 in mules and donkeys associated with respiratory disease and abortions have been documented, but the neurologic form has not been reported.
In a North American survey, the incidence of the neurologic form of equine herpesvirus-1 is rare; a report from 17 teaching hospitals in North America from 1984-2003 showed an incidence of 0.22 cases per 1,000 horses.
Couetil said prior to the first case of neurologic disease, there often is a history of respiratory disease, abortion, fever, inappetence, hind limb edema, or foal disease within the previous two weeks. In many cases, neurologic deficits such as ataxia (incoordination) are the first signs.
"Clinical signs vary from mild ataxia to complete paralysis of the hind limbs and recumbency," he said. "Tail and anus hypotonia (diminished muscle tone) and bladder paralysis with incontinence are frequently noted. Neurologic deficits are usually bilaterally symmetric, but not always, and hind limbs are generally more severely affected than front limbs. Affected stallions may present with hind limb edema, reduced libido, testicular swelling, penile flaccidity, paraphimosis (retraction of the foreskin over the penis, allowing it to dry out), or repeated erections. Bladder paralysis may result in complications such as urine scalding and cystitis. Signs of uveitis (eye inflammation) with hypopyon (pus in the eye) and respiratory and gastrointestinal disease have been reported in foals during an outbreak of EHV-1.
"In severely affected horses, progression is usually rapid with paralysis and recumbency developing within the first 24-48 hours," Couetil noted. "Mildly affected horses frequently stabilize quickly and recover fully within days to weeks."
Couetil said that good quarantine management is the key to preventing an outbreak. New horses should be isolated for three weeks before being allowed to mix with the farm's population. In the event of EHV-1 clinical signs, "Strict isolation protocols should be implemented as soon as a presumptive diagnosis of EHV-1 is made," he stressed. "Isolation protocols are aimed toward prevention of the spread of the virus among horses by separating aborting mares, sick newborns, and any horse exhibiting fever, nasal discharge, or gait deficits from the herd. All movement on and off the premises should cease, and strict regulation should be put in place concerning visitors.
"Recently foaled mares and pregnant mares should be divided into small groups as soon as possible," advised Couetil. "Any aborted fetus and fetal membranes should be sealed in plastic bags and submitted to a diagnostic laboratory. Sanitary barriers should be put in place around isolated horses, including the use of disinfectants, protective clothing, disposable gloves, and waterproof footwear. Cleaning of the facilities and equipment should be conducted with water and detergent to remove organic debris. Follow this by disinfection with germicidal compounds. Phenolics are recommended because of their efficacy in the presence of organic matter, however, hypochlorites (bleach) and quaternary ammonium compounds may be used on cleaned surfaces. Iodophores, but not chlorhexidine, may be used as a skin antiseptic. Equipment should not be shared between isolated animals and the rest of the herd. All horses should be observed daily for signs of EHV-1 infection.
"Vaccination of horses recently exposed to EHV-1 is not recommended because of the possibility for worsening of neurological signs," he noted. "However, vaccination of horses surrounding the affected premises should be considered. Unaffected horses should be kept isolated for a minimum of three weeks after recovery of the last clinical cases.
"The main therapeutic goals are reducing stress (e.g., stop breeding or training activities), providing supportive care, treating central nervous system inflammation, and preventing secondary complications," Couetil explained.
Horses showing neurologic deficits, but remaining standing, usually improve within a few days, he said. Horses that become recumbent for more than 24 hours have a poor prognosis. "However, the decision to euthanatize a recumbent animal should not be made too quickly because some may recover after being recumbent for days, provided they were given appropriate nursing care," Couetil said. "Return of urinary control often precedes gait deficit recovery, but it is not uncommon for horses to be left with neurologic deficits."
About the Author
Kimberly S. Brown was the Publisher/Editor of The Horse: Your Guide To Equine Health Care from June 2008 to March 2010, and she served in various positions at Blood-Horse Publications since 1980.