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The Modern

Equine Vet www.modernequinevet.com

Vol 10 Issue 6 2020

EHV: A Tale of 2 Treatments Ask the Nutritionist? When Should I Suggest a Hay Analysis? Testing Asymptomatic Carriers of S. equi Safer Entrance to Caudal Pouches of Femorotibial Joint




A Tale of 2 Treatments: 4 Aspirin and Acyclovir During an EHV-1 Outbreak Cover: Shutterstock/Shawn Hamilton


When should I recommend my client obtain a hay analysis, and what forage analysis labs do you recommend? How do I help my client interpret the results?........................................................................................................... 3 WOUND CARE

Location is Everything ..................................................................................................................10 INFECTIOUS DISEASES

Using Antibody Titers in Vaccine-Averse Cases.....................................................................12 NEWS NOTES

Is There a Safer Entrance to Caudal Pouches of the Lateral Femorotibial Joint? ..... 8 Is Serology the Right Test for Asymptomatic S. equi carriage?......................................... 9 Identifying Cyathostomin Burdens..........................................................................................15

ADVERTISERS Purina Sponsored Content.........................................3 Merck Animal Health..................................................5 American Regent Animal Health/Adequan...........9

Shanks Veterinary Equipment..................................8 AVMA PLIT......................................................................9 AAEVT............................................................................13

The Modern

Equine Vet SALES: Matthew Todd • Lillie Collett EDITOR: Marie Rosenthal ART DIRECTOR: Jennifer Barlow CONTRIBUTING WRITERS: Paul Basillo • Adam Marcus COPY EDITOR: Patty Wall Published by PO Box 935 • Morrisville, PA 19067 Marie Rosenthal and Jennifer Barlow, Publishers PERCYBO media  publishing


Issue 6/2020 | ModernEquineVet.com

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Ask the



Ask the Nutritionist is a monthly column featuring questions answered by PhD equine nutritionists and sponsored by Purina Animal Nutrition. Have a nutrition question you want to see featured? Email Marie Rosenthal. For clinics looking for specific nutritional advice, visit purinamills.com/ask-an-expert.

When should I recommend my client obtain a hay analysis, and what forage analysis labs do you recommend? How do I help my client interpret the results? You might recommend a forage analysis when managing the diet of a horse with sugar and starch sensitivities, when treating a horse experiencing chronic colic or digestive upset, or if you suspect a potential nutrient deficiency or toxicity (i.e., selenium). Obtaining a forage analysis is also a good practice to help owners better understand how forage contributes to their overall nutrition and feeding program, especially when hay is purchased in bulk. HOW TO TAKE A HAY SAMPLE For best results, obtain a representative sample of the entire hay batch. To do this, you’ll need to collect at least 6 core samples using 1 of these methods: 1. Hay probe powered by an electric drill or hand brace 2. Hand-grab technique Combine core samples, mix well, place a subsample into the sample bag and submit for analysis. Confirm the quantity needed for analysis with your laboratory. WHERE TO SEND A HAY SAMPLE Equi-Analytical Laboratory Services is an example of a reputable commercial lab specializing in horse forage analysis, but there are many others. Most states have a forage testing lab for their residents. Check with your county extension agent or state university for information. When submitting the sample, you may be asked to select a preferred analytical method. Near-infrared technology (NIR) is adequate for most purposes. When a precise analysis is needed (i.e., mineral analysis), traditional analytical (wet chemistry) methods are preferred. HOW TO INTERPRET A HAY ANALYSIS Interpreting a hay analysis can be simple or complex, depending on the reason for testing.

When screening hay for use in the diets of horses with sugar and starch sensitivities, a good rule of thumb is to target an ethanolsoluble carbohydrate (ESC) and starch level of 12% or less. Screening hay for sensitive horses (those with a history of chronic colic or digestive issues) is less straightforward. Because the consumption of overly mature hay can easily lead to colic in sensitive horses, choose good-quality hay that was harvested properly, isn’t overly mature and provides adequate fiber and calories. On a feed analysis report, the relative feed value (RFV) serves as a good benchmark to assess overall hay quality. A higher RFV tends to reflect higher quality hays with greater digestibility and calorie content. For sensitive horses, feeding hay with an RFV of ≥87, neutral detergent fiber (NDF) of ≤60 (as fed basis) and acid detergent fiber (ADF) of ≤42 (as fed basis) is recommended. When obtaining a hay analysis in a suspected mineral deficiency or toxicity situation, use the forage mineral concentration paired with daily amount fed to calculate total daily intake. In more complex cases, consult with an experienced equine nutritionist to assist with forage analysis interpretation. Contact a Purina PhD nutritionist for a complimentary consultation through Purina Customer Service, 800-227-8941 or send us a message at www.purinamills.com/ask-an-expert.

UPCOMING TOPICS July: Colic August: Lameness September: Cardiology

Have a question you want to see featured? Send them to modernequinevet@gmail.com.

ABOUT THE AUTHOR Dr. Kelly Vineyard is a senior nutritionist, equine technical solutions, with Purina Animal Nutrition. She provides expert technical nutrition advice and insights in a variety of areas, including new product innovation, product research and veterinarian and customer technical support. SPONSORED BY PURINA ANIMAL NUTRITION

ModernEquineVet.com | Issue 6/2020



A Tale of 2 Treatments:

Aspirin and Acyclovir During an EHV-1 Outbreak Equine Herpesvirus-1 (EHV-1) is endemic to the

North American horse population, with more than 80% of horses exposed to the virus by age 2. However, few treatments have been evaluated during naturally occurring outbreaks. Susannah S. Lewis, DVM, PhD, of the Rainland Farm Equine Clinic in Woodinville, Wash., recently experienced such an outbreak firsthand. She spoke about the effect of antiviral and anticoagulant treatment at a 60-horse boarding and training farm at the 65th Annual AAEP Convention in Denver.

Shutterstock/gibleho Shutterstock/Zadorozhnyi Viktor

Neurotropic strain

The index case underwent a respiratory panel for 5 common respiratory pathogens via nasal swab PCR. Results were positive for EHV-1 G2254, which is known as the neurotropic strain due to the higher rate of neurologic disease. This strain is also known to cause abortion, but luckily there were no pregnant mares on the farm at the time, she said. “Our index case had a fever at day 0, and then it progressed,” Dr. Lewis said. “It was a weekend and there was a shipping delay, so we didn’t get the results back

B y 4

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from the nasal PCR swab until day 6. At that point, the horse had recovered.” EHV-1 G2254 typically causes fever and mild respiratory signs. The main worry was the neurologic complications that usually arise. “Equine herpes myeloencephalitis [EHM] is due to a vasculitis,” Dr. Lewis explained. “There’s inflammation in the blood vessels, which triggers the coagulation cascade, which leads to microthrombi forming in the spinal cord. That leads to ischemic injury and neurologic signs.” Flaccid paralysis typically starts at the back of the horse and moves forward. Clients were instructed to take the horse’s temperature twice daily, and to be on the lookout for loose, floppy tails. “All of our neurologic cases had some grade of hind limb ataxia, and we had a number that lost control of their urinary sphincter,” she said. “You need to pass a catheter to allow the bladder to void.” Ataxia can progress to all limbs and result in recumbency, and severe cases can have flaccid paralysis of the respiratory muscles. These are typically the horses that cannot be saved, she said.

M B a y r i Pe a uR lo s B e a n s t i h l ai lo ,


The Science of

CONVENIENT PROTAZIL® (1.56% diclazuril) Antiprotozoal Pellets is the only FDA-approved alfalfa-based top dress antiprotozoal pellet for the treatment of EPM. • Equine Protozoal Myeloencephalitis (EPM) is a serious neurological disease that can strike anytime, anywhere. Make treatment easy with PROTAZIL® • Safe and accurate dosing with a calibrated scoop • Easier to use than paste, less stress for you and your horse • Rapid absorption — no loading dose required1 Now that’s convenient.

Ask your Merck Animal Health Equine representative about PROTAZIL® or call 800-521-5767. IMPORTANT SAFETY INFORMATION: Use of PROTAZIL® (1.56% diclazuril) Antiprotozoal Pellets is contraindicated in horses with known hypersensitivity to diclazuril. Safe use in horses used for breeding purposes, during pregnancy, or in lactating mares has not been evaluated. The safety of PROTAZIL® (1.56% diclazuril) Antiprotozoal Pellets with concomitant therapies in horses has not been evaluated. For use in horses only. Do not use in horses intended for human consumption. Not for human use. Keep out of reach of children.

2 Giralda Farms • Madison, NJ 07940 • merck-animal-health-usa.com • 800-521-5767 Copyright © 2020 Intervet Inc., d/b/a/ Merck Animal Health, a subsidiary of Merck & Co., Inc. All rights reserved.


Hunyadi L, Papich MG, Pusterla N. Pharmacokinetics of a low‑dose and DA‑labeled dose of diclazuril administered orally as a pelleted top dressing in adult horses. J of Vet Pharmacology and Therapeutics (accepted) 2014, doi: 10.111/jvp.12176. The correlation between pharmacokinetic data and clinical effectiveness is unknown

INFECTIOUS DISEASES FOR ORAL USE IN HORSES ONLY CAUTION Federal ( U.S.A.) law restricts this drug to use by or on the order of a licensed veterinarian. NADA #141-268 Approved by FDA DESCRIPTION Diclazuril, (±)-2,6-dichloro-α- (4-chlorophenyl)-4- (4,5-dihydro-3,5-dioxo-1,2,4triazin-2(3H )-yl)benzeneacetonitrile, has a molecular formula of C 17 H 9 CI 3 N 4 O 2 , a molecular weight of 407.64, and a molecular structure as follows:

Diclazuril is an anticoccidial (antiprotozoal) compound with activity against several genera of the phylum Apicomplexa. PROTAZIL® (diclazuril) is supplied as oral pellets containing 1.56% diclazuril to be mixed as a top-dress in feed. Inert ingredients include dehydrated alfalfa meal, wheat middlings, cane molasses and propionic acid (preservative). INDICATIONS PROTAZIL® (1.56% diclazuril) Antiprotozoal Pellets are indicated for the treatment of equine protozoal myeloencephalitis ( EPM) caused by Sarcocystis neurona in horses. DOSAGE AND ADMINISTRATION Dosage: PROTAZIL® (1.56% diclazuril) is administered as a top dress in the horse’s daily grain ration at a rate of 1 mg diclazuril per kg (0.45 mg diclazuril/lb) of body weight for 28 days. The quantity of PROTAZIL® necessary to deliver this dose is 64 mg pellets per kg (29 mg pellets/lb) of body weight. Administration: To achieve this dose, weigh the horse (or use a weigh tape)). Scoop up PROTAZIL® to the level (cup mark) corresponding to the dose for the horse’s body weight using the following chart: Weight Range mLs of Pellets of Horse (lb) 275 - 524 20 525 - 774 30 775 - 1024 40 1025 - 1274 50

Weight Range mLs of Pellets of Horse (lb) 1275 - 1524 60 1525 - 1774 70 1775 - 2074 80 -

One 2.4-lb bucket of PROTAZIL® will treat one 1274-lb horse for 28 days. One 10-lb bucket of PROTAZIL® will treat five 1100-lb horses for 28 days. CONTRAINDICATIONS Use of PROTAZIL® (1.56% diclazuril) Antiprotozoal Pellets is contraindicated in horses with known hypersensitivity to diclazuril. WARNINGS For use in horses only. Do not use in horses intended for human consumption. Not for human use. Keep out of reach of children. PRECAUTIONS The safe use of PROTAZIL® (1.56% diclazuril) Antiprotozoal Pellets in horses used for breeding purposes, during pregnancy, or in lactating mares has not been evaluated. The safety of PROTAZIL® (1.56% diclazuril) Antiprotozoal Pellets with concomitant therapies in horses has not been evaluated. ADVERSE REACTIONS There were no adverse effects noted in the field study which could be ascribed to diclazuril. To report suspected adverse reactions, to obtain a MSDS, or for technical assistance call 1-800-224-5318. CLINICAL PHARMACOLOGY The effectiveness of diclazuril in inhibiting merozoite production of Sarcocystis neurona and S. falcatula in bovine turbinate cell cultures was studied by Lindsay and Dubey (2000).1 Diclazuril inhibited merozoite production by more than 80% in cultures of S. neurona or S. falcatula treated with 0.1 ng/mL diclazuril and greater than 95% inhibition of merozoite production (IC 95 ) was observed when infected cultures were treated with 1.0 ng/mL diclazuril. The clinical relevance of the in vitro cell culture data has not been determined. PHARMACOKINETICS IN THE HORSE The oral bioavailability of diclazuril from the PROTAZIL® (1.56% diclazuril) Antiprotozoal Pellets at a 5 mg/kg dose rate is approximately 5%. Related diclazuril concentrations in the cerebrospinal fluid (CSF) range between 1% and 5% of the concentrations observed in the plasma. Nevertheless, based upon equine pilot study data, CSF concentrations are expected to substantially exceed the in vitro IC 95 estimates for merozoite production (Dirikolu et al., 1999) 2. Due to its long terminal elimination half-life in horses (approximately 43-65 hours), diclazuril accumulation occurs with once-daily dosing. Corresponding steady state blood levels are achieved by approximately Day 10 of administration. EFFECTIVENESS Two hundred and fourteen mares, stallions, and geldings of various breeds, ranging in age from 9.6 months to 30 years, were enrolled in a multi-center field study. All horses were confirmed EPM-positive based on the results of clinical examinations and laboratory testing, including CSF Western Blot analyses. Horses were administered PROTAZIL® (1.56% diclazuril) Antiprotozoal Pellets at doses of 1, 5, or 10 mg diclazuril/kg body weight as a top-dress on their daily grain ration for 28 days. The horses were then evaluated for clinical changes via a modified Mayhew neurological scale on Day 48 as follows: 0. Normal, neurological deficits not detected. 1. Neurological deficits may be detectable at normal gaits; signs exacerbated with manipulative procedures (e.g., backing, turning in tight circles, walking with head elevation, truncal swaying, etc.). 2. Neurological deficit obvious at normal gaits or posture; signs exacerbated with manipulative procedures. 3. Neurological deficit very prominent at normal gaits: horses give the impression they may fall (but do not) and buckle or fall with manipulative procedures. 4. Neurological deficit is profound at normal gait: horse frequently stumbles or trips and may fall at normal gaits or when manipulative procedures were utilized. 5. Horse is recumbent, unable to rise. Each horse’s response to treatment was compared to its pre-treatment values. Successful response to treatment was defined as clinical improvement of at least one grade by Day 48 ± conversion of CSF to Western Blot-negative status for S. neurona or achievement of Western Blot-negative CSF status without improvement of 1 ataxia grade. Forty-two horses were initially evaluated for effectiveness and 214 horses were evaluated for safety. Clinical condition was evaluated by the clinical investigator’s subjective scoring and then corroborated by evaluation of the neurological examination videotapes by a masked panel of three equine veterinarians. Although 42 horses were evaluated for clinical effectiveness, corroboration of clinical effectiveness via videotape evaluation was not possible for one horse due to missing neurologic examination videotapes. Therefore, this horse was not included in the success rate calculation. Based on the numbers of horses that seroconverted to negative Western Blot status, and the numbers of horses classified as successes by the clinical investigators, 28 of 42 horses (67%) at 1 mg/ kg were considered successes. With regard to independent expert masked videotape assessments,

10 of 24 horses (42%) at 1 mg/kg were considered successes. There was no clinical difference in effectiveness among the 1, 5, and 10 mg/kg treatment group results. Adverse events were reported for two of the 214 horses evaluated for safety. In the first case, a horse was enrolled showing severe neurologic signs. Within 24 hours of dosing, the horse was recumbent, biting, and exhibiting signs of dementia. The horse died, and no cause of death was determined. In the second case, the horse began walking stiffly approximately 13 days after the start of dosing. The referring veterinarian reported that the horse had been fed grass clippings and possibly had laminitis. ANIMAL SAFETY PROTAZIL® (1.56% diclazuril) Antiprotozoal Pellets were administered to 30 horses (15 males and 15 females, ranging from 5 to 9 months of age) in a target animal safety study. Five groups of 6 horses each (3 males and 3 females) received 0, 5 (5X), 15 (15X), 25 (25X) or 50 (50X) mg diclazuril/kg (2.27mg/lb) body weight/day for 42 consecutive days as a top-dress on the grain ration of the horse. The variables measured during the study included: clinical and physical observations, body weights, food and water consumption, hematology, serum chemistry, urinalysis, fecal analysis, necropsy, organ weights, gross and histopathologic examinations. The safety of diclazuril top-dress administered to horses at 1 mg/kg once daily cannot be determined based solely on this study because of the lack of an adequate control group (control horses tested positive for the test drug in plasma and CSF). However, possible findings associated with the drug were limited to elevations in BUN, creatinine, and SDH and less than anticipated weight gain. Definitive test article-related effects were decreased grain/top-dress consumption in horses in the 50 mg/kg group. In a second target animal safety study, PROTAZIL® (1.56% diclazuril) Antiprotozoal Pellets were administered to 24 horses (12 males and 12 females, ranging from 2 to 8 years of age). Three groups of 4 horses/sex/group received 0, 1, or 5 mg diclazuril/kg body weight/day for 42 days as a top-dress on the grain ration of the horse. The variables measured during the study included physical examinations, body weights, food and water consumption, hematology, and serum chemistry. There were no test article-related findings seen during the study. STORAGE INFORMATION Store between 15°C to 30°C (59°F to 86°F). HOW SUPPLIED PROTAZIL® (1.56 % diclazuril) Antiprotozoal Pellets are supplied in 2.4-lb (1.1 kg) and 10-lb (4.5 kg) buckets.

REFERENCES 1. Lindsay, D. S., and Dubey, J. P. 2000. Determination of the activity of diclazuril against Sarcocystis neurona and Sarcocystis falcatula in cell cultures. J. Parasitology, 86(1):164–166.

2. Dirikolu, L., Lehner, F., Nattrass, C., Bentz, B. G., Woods, W. E., Carter, W. E., Karpiesiuk, W. G., Jacobs, J., Boyles, J., Harkins, J. D., Granstrom, D. E. and Tobin, T. 1999. Diclazuril in the horse: Its identification and detection and preliminary pharmacokinetics. J. Vet. Pharmacol. Therap. 22:374–379. Intervet Inc d/b/a Merck Animal Health 2 Giralda Farms, Madison, NJ 07940 Copyright © 2020 Intervet Inc. a subsidiary of Merck & Co. Inc. All rights reserved.


07-2014 211.x.3.0.3

Issue 6/2020 | ModernEquineVet.com

On the first day that temperatures were collected following isolation of the pathogen, there were 7 horses with new fevers. With 8 horses shedding virus at that point, the farm knew they were in for the long haul. As the outbreak progressed, they had 44 fevers total. The average fever duration was 3 to 4 days, and the last fever was noted on day 27. There was about a 4½ day average delay between the onset of first fever and the onset of neurologic signs. A total of 12 horses had neurologic signs, and 7 of those were euthanized. “Our last neurologic case was on day 28,” Dr. Lewis said. It took 42 days from the last fever until the end of the state quarantine, which lasted 67 days, Dr. Lewis told The Modern Equine Vet. “The state quarantine started on day 6 when we had our first positive result, and temperatures were taken twice daily throughout. It was a treasure drove of data.”

The Study

In 33 of the horses with EHV-1 infection, valacyclovir 27 mg/kg PO 3 times daily was administered for 2 days, followed by 18 mg/kg PO twice daily for 10 days. The antiviral reduces shedding. Treatment was initiated within 3 days of the fever starting in 12 horses, and at more than 3 days after initial fever in 11 horses. Ten asymptomatic horses were given the drug, and 21 febrile horses did not receive it. “All of our horses were also treated with dexamethasone,” Dr. Lewis said. “I know it’s controversial because we’re giving steroids in the face of an infection. But we really never saw a horse improve until it was given dexamethasone. “After that, we got a little more aggressive and talked to some other internists for different takes on it,” she said. “We ended up giving dexamethasone to all of the horses, in addition to flunixin twice daily plus supportive care, such as vitamin E, urinary catheterization, and management for the down horses.” Results showed that valacyclovir did not affect the duration or magnitude of the fever—how long they had fever or how high the fever was—regardless of when treat6

Issue 6/2020 | ModernEquineVet.com

ment was initiated. It also did not affect the number of cases that progressed to EHM. “Our clinical impression, however, was that when we started valacyclovir on a large number of horses, we saw a decrease in the number of new fevers,” Dr. Lewis added. “It's possible…that it reduces viral shedding enough that it inhibits the spread of the disease—not so much for the horse you’re giving it to, but for the horses around it. But we didn't have enough data to analyze that accurately.” Of the 12 horses with EHM, 8 were recumbent at 1 stage, and 5 survived overall. Two of the survivors had also been recumbent. While previous research has shown that older age was linked with a greater risk of EHM, the outbreak at this farm did not show that pattern. Nor was there a significant association between EHM and length or severity of fever. Aspirin has been used, but not widely, to reduce fever. “We figured we had a vasculitis, and we know we have the activated coagulation cascades, and aspirin was something that was orally bioavailable and we could readily buy,” she explained. Aspirin did significantly decrease the proportion of EHM cases that were euthanized. Eight horses that had EHM were not given aspirin. Six of those horses became recumbent, and 7 were euthanized. “Of the 4 cases that were given aspirin, 2 became recumbent and none were euthanized.” she said. “The odds of being euthanized were 45 times higher if the horse was not given aspirin than in the horses that were.” She noted that the n of this study was small and there was a temporal selection bias. Once the decision was made to give aspirin, all of the EHM horses were given it. “I cross my fingers that this is going to be a fruitful area of future study, and that we can optimize these compounds in how we can use them to best manage a difficult disease,” she said. “In addition to implementation of effective farm biosecurity, it can help the course of the outbreak.” MeV


Veterinarians look at 2

MONTH: other drugs used for EHV-1

There’s nothing else like it. Over the past 30 years, Adequan® i.m. (polysulfated glycosaminoglycan) has been administered millions of times1 to treat degenerative joint disease, and with good reason. From day one, it’s been 2, 3 the only FDA-Approved equine PSGAG joint treatment available, and the only one proven to. Reduce inflammation Restore synovial joint lubrication Repair joint cartilage Reverse the disease cycle When you start with it early and stay with it as needed, horses may enjoy greater mobility 2, 4, 5 over a lifetime. Discover if Adequan is the right choice. Talk to your American Regent Animal Health sales representative or call (800) 458-0163 to order. BRIEF SUMMARY: Prior to use please consult the product insert, a summary of which follows: CAUTION: Federal law restricts this drug to use by or on the order of a licensed veterinarian. INDICATIONS: Adequan® i.m. is recommended for the intramuscular treatment of non-infectious degenerative and/or traumatic joint dysfunction and associated lameness of the carpal and hock joints in horses. CONTRAINDICATIONS: There are no known contraindications to the use of intramuscular Polysulfated Glycosaminoglycan. WARNINGS: Do not use in horses intended for human consumption. Not for use in humans. Keep this and all medications out of the reach of children. PRECAUTIONS: The safe use of Adequan® i.m. in horses used for breeding purposes, during pregnancy, or in lactating mares has not been evaluated. For customer care, or to obtain product information, visit www.adequan.com. To report an adverse event please contact American Regent, Inc. at (800) 734-9236 or email pv@americanregent.com. Please see Full Prescribing Information at www.adequan.com.

www.adequan.com 1 Data on file. 2 Adequan® i.m. Package Insert, Rev 1/19. 3 Burba DJ, Collier MA, DeBault LE, Hanson-Painton O, Thompson HC, Holder CL: In vivo kinetic study on uptake and distribution of intramuscular tritium-labeled polysulfated glycosaminoglycan in equine body fluid compartments and articular cartilage in an osteochondral defect model. J Equine Vet Sci 1993; 13: 696-703. 4 Kim DY, Taylor HW, Moore RM, Paulsen DB, Cho DY. Articular chondrocyte apoptosis in equine osteoarthritis. The Veterinary Journal 2003; 166: 52-57. 5 McIlwraith CW, Frisbie DD, Kawcak CE, van Weeren PR. Joint Disease in the Horse.St. Louis, MO: Elsevier, 2016; 33-48. All trademarks are the property of American Regent, Inc. © 2020, American Regent, Inc. PP-AI-US-0372 02/2020


Is There a Safer Entrance to Caudal Pouches of the Lateral Femorotibial Joint? Arthroscopic view of the right cranial compartment of the lateral femorotibial joint. The trajectory into the lateral recess is marked by the green circle, and is located within the center of a triangle bounded by the lateral femoral condyle (LFC), cranial horn of the lateral meniscus and associated meniscotibial ligament (LM) and finally the combined body of the long digital extensor tendon and peroneus tertius (LDE/PT)

Images courtesy of Equine Veterinary Journal

Compared with other synovial compartments of the stifle, arthroscopic approaches to the caudal pouches of the lateral femorotibial joint are more challenging. The surgeon risks complications such as damaging the iatrogenic nerve and cartilage. Surgeons found that an arthroscopic portal immediately cranial to the lateral collateral ligament permitted consistent entry into the popliteal tunnel and both pouches of the caudal lateral femorotibial joint, resulting in fewer complications This cadaver and clinical study described and evaluated a novel arthroscopic approach to the caudal pouches of the lateral femorotibial joint as current approaches are considered challenging and risky.

Anatomic dissection with the arthroscope and cannula in situ for the described lateral portal. The proposed skin portal (yellow circle) is located on the cranial aspect of the lateral collateral ligament (LCL) and caudal to the combined origin of the long digital extensor tendon and peroneus tertius (LDE/PT). The lateral femoral condyle (LFC) and lateral meniscus (LM) have been outlined, in addition to the tendinous and muscular portions of the popliteus (Pop; outlined by green dashed lines)

The surgical technique was developed initially using 19 cadaver limbs positioned to simulate dorsal recumbency and with the stifle held in 90° flexion. A portal was made immediately cranial to the lateral collateral ligament and the arthroscope advanced along the popliteal tunnel of the femorotibial joint in a cranial to caudal direction. Following the cadaver study, 33 horses underwent inspection of 38 caudal lateral femorotibial joints using the alternative technique as part of routine joint inspection in 33 horses. Entry and examination of both pouches of the caudal lateral femorotibial joint were consistently achieved in both the cadaver and clinical limbs, with no intra- or post-operative complications in the latter. MeV

For more information:

Lifting Large Animals Since 1957 www.shanksvet.com


Issue 6/2020 | ModernEquineVet.com

O’Neill HD, Bladon BM. An alternative arthroscopic approach to the caudal pouches of the equine lateral femorotibial joint. Equine Vet J. 2020 May 4 (Epub ahead of print). https://beva.onlinelibrary.wiley.com/doi/10.1111/ evj.13274

Is Serology the Right Test for Asymptomatic S. equi Carriers? Veterinarians might not be able to rely on serological testing for Streptococcus equi, which causes strangles, as a way to identify asymptomatic carriers. Asymptomatic carriage within the guttural pouch is considered a major factor in the persistence of this highly infectious disease. Researchers performed a retrospective study to investigate the sensitivity of serological testing for antibodies against S. equi subspecies equi antigens A and C in detecting carriers from 287 horses arriving at a welfare charity quarantine unit that underwent microbiological sampling of guttural pouches. They reviewed the serological testing results and found 9 (3.1%) horses were found to be guttural pouch carriers on microbiology, and 35 (12.2%) horses were sero-

positive (had at least one ELISA OD value ≥0.5). Of the 35 seropositive horses, 1 (2.9%) had evidence of S. equi in a guttural pouch lavage. Of the 252 horses with OD values <0.5, 8 (3.2%) had evidence of S. equi in guttural pouch samples. Only 1 (11%) of the 9 horses found to be a carriers was seropositive at a cut-off of OD ≥ 0.5, but lowering the cut-off to OD ≥ 0.3 identified 2 additional carriers. Serology is a common way of identifying asymptomatic carriers of S. equi, but this study means veterinarians cannot rely on seronegativity to antigens A and C when determining if a horse is a chronic carrier of S. equi. The researchers said the most reliable method for determining carriage is microbiological sampling. MeV

For more information: Durham AE, Kemp-Symonds J. Failure of serological testing for antigens A and C of Streptococcus equi subspecies equi to identify guttural pouch carriers. Equine Vet J. 2020 May 6 (Epub ahead of print). https://beva.onlinelibrary.wiley.com/doi/10.1111/evj.13276

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Location is Everything B y

S a c h a

A d o r n o

Photo by Shannon Brinkman

Lafite, aka Flip Flop, and his rider/owner

Liza Horan were having a great round at Fair Hill International when an accident mid-course led to potentially career- or even life-threatening injuries for the 12-year-old warmblood gelding. “The jump was pretty straightforward, and I thought I had a good shot as far as my approach and distance. It seemed that Flip Flop would jump it quite easily. But when he started to leave the ground, he grabbed his left front shoe in a way that felt like it nailed his leg to the floor,” explained Ms. Horan, who trains at Ironwood Ranch in Lompoc, Calif., and made the trip with 3 horses to Maryland for the October 2019 event. “His front leg didn’t come off the ground, and he hit the rail of the jump really hard. He went almost vertical with his hind legs and made a heroic effort not to fall down.” Although the horse succeeded in not falling, Ms. Horan was unseated during the accident. Medics attended to her, while Flip Flop galloped away, seemingly unphased. “He didn’t appear frantic when he took off,” Horan explained. “But I realize now he was a bit spooked by my fall—I'd never fallen from him.” After medics cleared her, Ms. Horan went looking for her horse, who had gotten off course. When horse and rider were reconnected later in the stables, “he looked like he’d been hit by a semi-truck,” Horan said. “He had multiple wounds and lacerations inconsistent with the accident. A few people saw him on the Fair Hill grounds—we know at 1 point he was in the parking lot and hit a parked car—but we don’t have a full picture of those minutes after the accident.” Flip Flop needed immediate medical attention, leaving no time for Ms. Horan to retrace his steps. Bernadette K. L. Smith, DVM, MS, an associate at Equine Veterinary Care at Fair Hill Training Center examined him 10

Issue 6/2020 | ModernEquineVet.com

Rider Liza Horan and her horse Flip Flop had a mysterious accident at Fair Hill International. Liza walked away unharmed. Flip Flop suffered injuries while fleeing the course.

Not all of Flip Flop’s injuries were life-threating. The serious lacerations were almost invisible on photos, while the bloodier ones (like these) required stitches but weren’t too risky.

and found wounds on all 4 legs. Several were in areas that, if infected, could have meant a poor prognosis. Although some of them looked gory, not all of Flip Flop’s injuries were life-threating. The dangerous lacerations were almost invisible on photos, while the bloodier ones required stitching but weren’t too risky. “The locations of his lacerations were a big red flag,” Dr. Smith said. “Not for the size of them but for where they were on his body—any lacerations on a horse are potentially career- or life-ending, it depends on the location and which structures are involved. Some of Flip Flop’s cuts were near joints—a terrible location—and he needed immediate specialty care.” Dr. Smith referred him to New Bolton Center, in Kenneth Square, Pa., so his case would have the full attention of multiple specialists who could make any necessary tests and treatments coordinated and swift. She said that it was almost always in the best interest of the horse with injuries like this to be referred. At New Bolton Center, Maia R. Aitken, DVM, DACVS, DACVECC, assistant professor of clinical emergency and critical care, immediately assessed the full extent of his injuries and checked all his vitals; heart and respiratory rates and temperature were normal. “He was walking well, but with trauma there can be a lot of adrenaline that can mask underlying damage,” said Dr. Aitken. “So, we took several radiographs to look for signs of fractures and found none. And then we systematically looked carefully at each joint, each wound, and the joints close to each wound.” In a full accounting of his injuries, the horse had lacerations on his left axillary region, left proximal antebrachium and left front heel bulb, where he had clipped his heel during the accident. He also had a large laceration at the inside of his right stifle and gaskin as well

Flip Flop recovered at New Bolton Center and at home without a care in the world.

as his left hind pastern. There were also 2 very small lacerations over his right carpus that did communicate with the radiocarpal joint. “These were the smallest lacerations but also held the most risk,” Dr. Aitken said. “I can’t stress enough that prognosis is all about location, location, location. Flip Flop had a large wound over his armpit, which involved a lot of suturing but wasn’t a great risk to the horse. Yet the 2 1-cm lacerations over his carpus looked like no big deal but were the most threatening because of the potential for infection.”

A Stitch in Good Time...

Flip Flop arrived at New Bolton Center within the window of time where—with specialized and aggressive emergency care—his wounds were treatable. Under anesthesia, the radiocarpal joint was lavaged with a large volume of sterile fluid and injected with antimicrobials to avoid infection. In addition, each wound was thoroughly debrided and lavaged and then meticulously closed with numerous sutures. All of his repaired lacerations were bandaged, and he was moved to a padded recovery stall. “He recovered uneventfully from the anesthesia and was an absolutely perfect patient while he was with us,” Dr. Aitken said. In the postoperative period, Flip Flop was treated aggressively with systemic and local antimicrobials as well as pain medication, wound care and bandaging. After a week in the hospital, Flip Flop was ready for the long trip back to the West Coast. The missing minutes are still a mystery, but the horse didn’t appear too concerned and made a full recovery. MeV This article original appeared in Bellwether Spring 2020. https://bit.ly/314Z9oL-MeV ModernEquineVet.com | Issue 6/2020




Antibody Titers

to Determine DOI in Vaccine-Averse Cases B y

P a u l

B a s i l i o

Shutterstock/Roman Zaiets

A well-managed horse receives a lot of antigens.


Between tetanus, Eastern and Western equine encephalomyelitis (EEE/WEE), rabies, West Nile virus, influenza, equine herpes virus-1 (EHV-1) and EHV4, and whatever risk- and region-based vaccines is indicated, the number of vaccine antigens that a horse is exposed to can be even greater than the number dogs receive. While AAEP guidelines and vaccine data sheets must be followed to ensure that a horse is properly vaccinated, an increasing number of owners express

Issue 6/2020 | ModernEquineVet.com

concern at the frequency and number of vaccines their horses receive, particularly with horses that have experienced an adverse reaction in the past. The decision to use a particular vaccine is based on an assessment of risk versus benefit, but if a client questions the necessity of a particular vaccine, measuring antibody titers might provide useful information on which to base the decision to either go ahead and vaccinate now or delay until a later date, according to W. David Wilson, BVMS, MS, Hon DACVIM, Department of Medicine and Epidemiology, School of


Veterinary Medicine, UC Davis. “I have been asked many times by horse owners and veterinarians, ‘if we vaccinate dogs against rabies every 3 years why do we need to vaccinate horses every year?’” Dr. Wilson said. “For tetanus, we revaccinate horses every year, whereas the interval in people often extends to 10 years, depending on the risk.” Horses typically have excellent responses to rabies and tetanus vaccines. If local reactions do occur, nonsteroidal anti-inflammatory drugs (NSAIDs) and hot or cold packs can help. For local or systemic reactions, switching to a vaccine with a different adjuvant in the future might do the trick. “At the end of the day, we have to look at the risk and consequences of infection vs. the risk and consequences of a vaccine reaction,” he explained here at the 65th Annual AAEP Convention in Denver. “Under those circumstances, a good approach may be to assess the immune status of the horse and re-vaccinate based on what we hope is a good correlate, or measure, of protection.” At this point, measuring antibodies in serum is the most feasible way to test the immune status of a horse, even though it does not assess all aspects of the immune response. For some diseases, antibody levels are good predictors of protection, whereas for others they are not.


Tetanus is a potent antigen in horses, and antibody levels do correlate with protection. A level of >0.01 IU/mL is considered to be protective, and it persists for more than 1 year after a 2-dose primary series in horses older than 6 months of age. After the third dose, protective levels can persist from between 2 years to more than 10 years, depending on the horse, he said. “Once the booster is administered, tetanus has a prolonged duration of immunity [DOI] that used to be measured via mouse inoculation test,” he said. “Thankfully, the Cornell Animal Health Diagnostic Center now has a toxin-binding ELISA that gives us an opportunity to measure tetanus antibodies. There is a stall-side test in Germany…that can determine whether it’s a good idea to administer a booster during an examination or whether the horse can wait a year or more. I have no experience with the stall-side test, but I find it intriguing.”

EEE/WEE and West Nile

Correlates of protection against EEE/WEE are not well established, but circulating virus antibodies likely play a role, because infection is acquired by vascular injection due to a mosquito bite, according to Dr. Wilson. Current inactivated vaccines appear too ef14

Issue 6/2020 | ModernEquineVet.com

ficacious if administered as recommended. “For EEE/WEE and West Nile virus, revaccination based on antibody titers is not recommended,” Dr. Wilson said. “Boosters are still required annually—especially with EEE, where it is every 6 months or so in the Southeastern US where the risk is high year-round.” A positive serum plaque reduction neutralization test (PRNT) titer against EEE or WEE provides evidence that the horse has been previously infected with, or vaccinated against, the pathogens, but the magnitude of the titer does not reliably predict protection, he said. The test is available through the National Veterinary Service Laboratory (NVSL) in Ames, IA. “The lab does not report a specific titer, but 3 ranges (<10, 10 to 100, and >100),” he explained. “A titer less than 10 means that the animal is likely susceptible, but that’s not based on a lot of controlled research.” A horse with a PRNT titer of >100 is unlikely to be susceptible. PRNT titers for WNV follow a similar pattern. “I wouldn't necessarily use this to guide vaccination, except in horses that had low titers and in horses that reacted adversely to vaccination in the past,” Dr. Wilson added.


“The primary rationale for vaccination of horses against rabies is protection of human health and other public health reasons,” he said. “The secondary rationale is protection of horses against this low-incidence disease.” Thanks to vaccination, rabies is rare. Of the more than 9 million horses and donkeys in the United States; 13 rabid horses and donkeys were reported to the CDC in 2018, which is similar to the number reported in 2017. In 2019, rabies was found in a horse in New Jersey and all of the people who handled the horse required post-exposure prophylaxis. Like tetanus, the inactivated rabies vaccine is a potent antigen in horses. There is an excellent serologic response after primary vaccination, although a few horses appear to be non-responders. Maternal antibody interference (interference of the vaccine response of the foal due to antibodies passed from the dam in colostrum) is also profound with rabies, which can present a dilemma for those veterinarians who follow the label. “The label states that the vaccine is for healthy horses 3 months of age or older,” Dr. Wilson noted. “Maternal antibody interference lasts at least 6 months. I wouldn’t be rushing to vaccinate foals against rabies until they’re at least 6 months of age. At that age they usually develop a robust response that results in prolonged level of antibodies following booster vaccina-

tion within the following year.” Although a specific level of antibody that confers protection in horses has not been defined, a level 0.5 IU/mL works well as the threshold in humans and dogs. It is likely similar in horses, he said. In a recent JAVMA-published study, Dr. Wilson and colleagues found that revaccination of previously vaccinated, non-pregnant horses, resulted in titers that persisted above the 0.5 IU/mL threshold for at least 2 to 3 years.

“This antibody lasts a long time,” he said. He did caution, however, that even though the titers may present 1 side of the story, horses that are vaccinated for rabies less often than once yearly are not considered to be properly vaccinated from a public health standpoint. “If that horse bites a person and the public health authorities are notified as they should be,” he said, “then that horse will likely be quarantined.” MeV

For more information: Harvey AM, Watson JL, Brault, et al. Duration of serum antibody response to rabies vaccination in horses. J Am Vet Med Assoc. 2016 Aug 15;249(4):411-8. doi: 10.2460/javma.249.4.411. PMID: 27479286 https://avmajournals.avma.org/doi/full/10.2460/javma.249.4.411?url_ver=Z39.88-2003&rfr_id=ori:rid:crossref. org&rfr_dat=cr_pub%20%200pubmed

Identifying Cyathostomin Burdens A new antigen may be important in accurately identifying cyathostomin burdens when combined with previously identified cyathostomin antigens in an enzyme linked immunosorbent assay (ELISA) detecting cyathostomin-specific IgG(T) antibodies in horse serum. This 3-antigen cocktail is being used to develop a commercial test to detect all stages of the small redworm life cycle, including the encysted larval phase. Until now it has not been possible to test for encysted small redworm as fecal egg counts only detect the presence of egg-laying adult worms. The researchers obtained cyathostomins from naturally infected horses, which had been collected for other research projects, and used them to experimentally infect horses. Then they collected sera from these animals at various stages of infection and compared these samples with those taken from horses that did not have helminths. The researchers wanted to define serum immunoglobulin G(T) responses to 2 antigens from the most common species. They tested 3 cocktail combinations: Cy-GALA proteins from 2 species and a Cy-CID protein from a third species (CT3); Cy-GALA proteins from 5 species (CT5); all CT5 components, plus a CyCID protein from an additional species (CT6).

The best predictive values for infection were obtained using CT3 and CT6, with similar values achieved for both. There are only 2 active ingredients licensed in the United States to treat encysted small redworm. To protect their effectiveness, targeted treatment programs will help ensure that the dewormers are only administered when needed, according to Jacqui Matthews, PhD, FRSB, FRCVS, RCVS, chief Technology Officer at Roslin Technologies in Edinburgh, Scotland, and the inventor of the test. Blood test results with historical fecal egg count results and assessment of grazing management would provide more information to enable veterinarians to make decisions about treating an individual horse or group, according to the researchers. MeV

Encysted cyathostomin larvae in the gut wall of an infected horse

Right now, the small redworm blood test is only available in the United Kingdom from Austin Davis Biologics in Scotland. https://www.austindavis.co.uk/small-redwormblood-test.

For more information: Tzelos T, Geyer KK, Mitchell MC, et al. Characterisation of serum IgG(T) responses to potential diagnostic antigens for equine cyathostominosis. Int J Parasitol. 2020 March 12 https://www.sciencedirect.com/science/article/abs/pii/S0020751920300382 ModernEquineVet.com | Issue 6/2020


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