The Modern
Equine Vet www.modernequinevet.com
Vol 10 Issue 9 2020
Should You Test for Fungus in Asthma? Ask the Nutritionist Diet's Role in Kidney Failure Management Preventing Breakdown on the Track Should Your Horse Be Taking a Cold Shower? Technician Update: Reaction to Penicillin
Check Out: Using Serum Amyloid A Protein Testing
TABLE OF CONTENTS
NEWS
COVER STORY
Preventing Fractures Among Race Horses..................8 Cannabis Guide for Animals................................12 Controversial Bill to Protect Racehorses.................13
4 Equine Asthma:
Don’t Forget the Fungi Cover: Shutterstock/Au_Cr
ASK THE NUTRITIONIST
What Role Does Nutrition Play in Both the Recovery from Acute Kidney Failure and Management of Chronic Kidney Failure?.......................................................... 3 NEW FEATURE
Incorporate SAA Testing with Stablelab Into Your Clinical Exams................................... 7 SPORTS MEDICINE
What’s the Best Cool-Down After Exercise?...........................................................................10 INFECTIOUS DISEASES
Experimental S. equi Vaccine Appears Effective..................................................................14 TECHNICIAN UPDATE
Tachycardia Under Anesthesia—a Reaction to Potassium G Penicillin ....................16
ADVERTISERS Purina Sponsored Content.................................................................................3 American Regent Animal Health/Adequan...................................................5 Zoetis Sponsored Content..................................................................................7 Merck Animal Health..........................................................................................9
Zoetis/iSTAT.........................................................................................................11 Epicur Pharma....................................................................................................13 AVMA PLIT............................................................................................................15 Equine Regenerative Medicine & Orthobiologics Summit.......................17
The Modern
Equine Vet SALES: Matthew Todd • Matthew Gerald 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
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Ask the
Nutritionist ANNA PESTA, PH.D., EQUINE TECHNICAL SOLUTIONS, PURINA ANIMAL NUTRITION
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.
What role does nutrition play in both the recovery from acute kidney failure and management of chronic kidney failure? ACUTE KIDNEY DISEASE Acute kidney injury or acute renal failure (ARF) can occur at any age in otherwise healthy horses. It’s caused by injury from nephrotoxic medications or environmental toxins, or it may develop secondary to another issue that has caused low blood volume. Most horses with ARF have very poor appetites and, due to metabolic effects of low energy intake, exhibit hyperglycemia and hypertriglyceridemia. This decreased intake, combined with impaired amino acid uptake, leads to muscle catabolism. Therefore, the primary nutritional goal for supporting horses through recovery is to limit protein and energy-wasting by simply keeping them eating. Provide a variety of palatable feedstuffs, especially green grass, to encourage voluntary intake. If that fails, it may be necessary to provide enteral nutrition through a slurry of blended feed, like Purina® Equine Senior® feed, or a balanced preparation, such as Wellsolve® Well-Gel® horse supplement. If the horse exhibits electrolyte imbalance and is wasting sodium and chloride in the urine, offer saltwater (a 0.45% NaCl solution) in addition to plain water. You also can topdress feed with plain, loose salt (10 g NaCl per 100 kg BW per day). CHRONIC KIDNEY DISEASE Most commonly, chronic kidney disease (CKD) is discovered during an evaluation for unexplained weight loss. However, in performance horses, the first signs may be as subtle as a poor coat or decreased performance. Your goal is to improve and maintain body condition and to manage blood urea nitrogen (BUN) levels for as long as possible. As with acute cases, appetite is often a significant challenge and recommendations for intake of certain nutrients must be balanced with the need for energy intake. At a certain point, it is more important that the horse eats rather than worrying about what they eat! Renal diets have been used with positive results in small animals for decades, but recommendations for equine diets are still evolving. Protein intake does not need to be as restricted as recommended in the past, but it needs to be managed to meet—and not greatly exceed—NRC requirements. Protein should be monitored through BUN to creatinine ratio (values over 15 mg/dl or below 10 mg/dl indicate excessive or inadequate protein intake, respectively). Green pasture is the preferred diet foundation. If hay is fed, grass hay is best
due to lower protein and calcium content. Feed alfalfa if it is all the horse will accept because it may stimulate the horse’s appetite for grass hay. Quality forage, plus a vitamin and mineral supplement, can be an appropriate diet. More commonly, though, caloric intake is a challenge and supplementation with concentrates is necessary. Oats have been long favored due to their nutrient profile and palatability, but a low-protein, textured feed such as Purina® Omolene® 100 feed is a balanced and complete alternative. Fat supplementation also can help meet energy requirements in horses without severe hyperlipidemia. There are positive data in other species to support the benefits of omega-3 fatty acids and antioxidants (another benefit of pasture, which is a good source of both). Horses with CKD have disturbed calcium regulation, and the goal is to meet, not exceed, dietary requirements for calcium and phosphorus. Salt supplementation has been controversial. It may increase voluntary water intake, but the potential further damage to kidney function may negate this benefit in advanced cases. Finally, small amounts of forced exercise can help stimulate appetite and prevent muscle wasting. Incorporate exercise into management plans where appropriate. Creatinine is an important marker for the current status and prognosis of horses with CKD. When it is low to moderate, the primary nutritional consideration may be as simple as ensuring water intake. But when creatinine is high (>5 mg/dL), long-term emphasis should be on supporting body condition to maintain quality of life as long as possible. 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 October: Reproduction: Stallion needs November: Reproduction: Mare needs
Have a question you want to see featured? Send them to modernequinevet@gmail.com.
Reference and suggested additional reading: Schott, H. C. 2013. Urinary Tract Disease. In: Equine Applied and Clinical Nutrition, Ed. R. J. Geor, P. A. Harris, and M. Coenen. Saunders Elsevier, St. Louis, MO.
ABOUT THE AUTHOR Dr. Anna Pesta, PhD, is a nutritionist on the Equine Technical Solutions Team at Purina Animal Nutrition. She is a lifelong equestrian and actively competes her off-the-track Thoroughbred in three-day eventing. SPONSORED BY PURINA ANIMAL NUTRITION
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Equine Asthma Molds are among the most ubiquitous airborne particles in a horse’s environment, and they are often found hanging out in natural sources of forage and bedding. “Even horses kept outdoors on hay can still have attacks of equine inflammatory airway disease [IAD], or what we now call mild equine asthma” said Emmanuelle Van Erck, DVM, PhD, DECEIM, of the Equine Sports Medicine Practice in Waterloo, Belgium. Contact between fungal particles and the respiratory epithelium causes an immune system reaction that can lead to inflammation. “With fungi, the problem is that they’re not only pro-inflammatory pathogens, but they can also cause infection when they proliferate,” Dr. Van Erck said. “They can be allergenic, and they can also produce mycotoxins, which can cause problems with respiratory function at the level of the upper airways or at the level of the lower airways with bronchoconstriction.” All fungi have their preferred optimal temperaB y
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P a u l
B a s i l l i o
Shutterstock/Chaykovsky Igor
Don’t Forget the Fungi
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
RESPIRATORY
Discussion
Copyrighted image owned by Dr. Van Erck. Used with permission.
• Mycology lacks sensitivity • Cytology TW > BAL for detection of fungi ! Both TW + BAL required for diagnosis
ture at which to live and propagate, but the most problematic are those that are thermotolerant. They can proliferate at body temperature or even at a broader range of environmental temperatures. These types of fungi are known as aeroallergens and pathogens, and they are often the fungi that are used to obtain mycotoxins that are used in biological warfare.
Methods
To help identify the prevalence of fungal isolates in the horse and to get a broader picture of the disease course for IAD or equine asthma, Dr. Van Erck and her colleagues conducted a study of 731 horses evaluated at her ambulatory referral practice. “[Our practice] does equine sports medicine, but only from the internal medicine perspective,” she explained. “We have a high caseload of horses with poor performance or those that are referred for respiratory issues. For this study, we looked at our cases between the years 2013 and 2016. This covered a broad range of horses in Western Europe from Belgium, France, The Netherlands, Germany, and Switzerland—they were mostly competition horses with a majority of Warmbloods, but also a few leisure horses as well.” Results of tracheal wash (cytology, fungal culture, and bacterial culture) and bronchoalveolar lavage (cytology) were recorded. Since Dr. Van Erck’s practice is ambulatory, the study data included information about the horse’s environment (eg, bedding and forage) in addition to results of the clinical examination. In addition to the BAL and tracheal wash, airway endoscopy was performed and scored for pharyngitis and mucus characteristics. 6
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“This is the approach for our typical respiratory cases,” she said. “We do not do one or the other. We systematically do all 3.”
Results
“The results were quite surprising, as 88% of the horses presented with inflammatory airway disease/ mild equine asthma,” Dr. Van Erck said. “It’s partly explained by the fact that the majority of these horses were housed indoors permanently.” It’s important to note that these are all referral cases that were likely referred because of respiratory issues. The study researchers focused on the fungal elements in the tracheal wash, as there were much fewer fungal particles found on BAL. Approximately 55% of horses had a positive tracheal wash mycology result, and 81% had evidence of fungal elements inside the sample. “We did not find good agreement between mycology culture and fungal elements in the tracheal wash,” she said. “It’s actually quite difficult to get a fungus to grow in vitro.” Horses that had fungal elements on tracheal wash cytology were two times more likely to have mild equine asthma when compared with horses without fungal elements in their samples. The fungi identified were mostly thermophilic—the majority were Aspergillus and Penicillium, with rare Mucor or Candida. “Horses that had a positive mycology culture were twice as likely to have a positive bacterial culture,” she said. “There was a kind of conspiracy between these microorganisms. Apart from poor performance, there were no obvious clinical signs (eg, cough, nasal discharge, or
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Incorporate SAA Testing With Stablelab® Into Your Clinical Exams By Bobby Cowles, DVM, MS, MBA, Equine Technical Services, Zoetis
S
erum Amyloid A (SAA) is a major acute phase protein the liver produces in the face of inflammation caused by infection that’s changing the way equine veterinarians practice veterinary medicine. Within hours of the body being exposed to an infectious agent, the liver produces high enough levels of SAA that can be measured in the general circulation. Circulating SAA levels rise rapidly and dramatically into the hundreds and even thousands during infection. The obvious advantage of SAA is that veterinarians can rapidly diagnose patients with infectious conditions, often prior to visible or outward clinical signs, such as fever, nasal discharge, diarrhea, etc. And, as quickly and dramatically as SAA elevates, its levels also decrease quickly, by approximately 50% every 24 hours, once the infection is resolved, enabling serial monitoring of SAA to monitor the horses’ response to treatment over time.1,2 Monitoring response to treatment by measuring SAA daily or every other day is one of the most common ways equine practitioners use SAA. Repeat testing is extremely important to identify and track where within the typical response curve the horse is, in addition to identifying if SAA concentration is increasing or decreasing.
HOW TO TEST SAA USING STABLELAB®
Because one of the features of SAA is its “real-time” measurement of inflammation caused by infection, stall-side testing with results in 10 minutes is readily available with Stablelab® from Zoetis to provide practitioners with accurate and immediate results. The rapid stall-side diagnostic test for SAA can help practitioners detect infectious conditions quickly and guide treatment strategies for optimal outcomes and return to function. The faster an infectious condition is diagnosed, the quicker the veterinarian and barn staff can work together, instituting appropriate biosecurity protocols to minimize disease spread. SAA testing with Stablelab should be added to the physical exam as standard protocol to evaluate health in high-risk horses. If you can detect a horse as early as possible, you might have time to treat the horse to still be able to perform at the highest level.
LEARN MORE about testing SAA with Stablelab by talking with your Zoetis representative or visit Stablelab.com.
REFERENCES 1 Nolen-Walston R. How to Interpret Serum Amyloid A Concentrations, in Proceedings. American Association of Equine Practitioners 2015; 130-137. 2 Jacobsen S. Review of Equine Acute-Phase Proteins, in Proceedings. American Association of Equine Practitioners 2007; 230-235. All trademarks are the property of Zoetis Services LLC or a related company or a licensor unless otherwise noted. Stablelab is a registered trademark of Epona Biotech Limited, used under license. © 2020 Zoetis Services LLC. All rights reserved. STB-00088
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breathlessness) in the horses with fungal elements in their samples. However, in horses that had germinated spores that started to create branching hyphae, there was a higher likelihood for cough and epistaxis. When diagnosing fungal issues in horses with mild equine asthma, mycology is not the best option, because it lacks sensitivity. “You would need to do a combined tracheal wash and BAL cytology, because the tracheal wash will show you the presence of the fungal particles, and the BAL will allow you to detect the proportion of inflammation,” she said. Instead of a centrifuge, Dr. Van Erck’s practice uses a sedimentation technique to concentrate the
mucus from the horse’s airways. “We use a homemade system because we like to keep it easy to use,” she said. “We take 1-mL syringes with the head removed and pipette 0.7 µL in there, which allows us to have a concentration of cells on our slides. The fungal particles are usually entrapped in the mucus, so it’s important to look at the mucus instead of getting rid of it.” Dr. van Erck spoke at the 65th Annual AAEP Convention in Denver. Dr. Van Erck serves on the board of directors of Haygain, but was not in that position at the time this study was initiated and conducted.
In an anatomical comparison of the cannon bone among 3 horse breeds, researchers found that fostering adaptations in these bones through training might help prevent breakdown. About 70% of leg fractures during racing occur in the third metacarpal bone between the horse's knee and pastern. Deanna Goldstein, a doctoral candidate in the Center for Functional Anatomy and Evolution at Johns Hopkins Medicine, compared the sizes, densities and abilities to bend without breaking of canon bones from Thoroughbreds, American Quarter Horses and Assateague Island ponies. She and her colleagues wanted
to know how each breed's lifestyle and training affected the bone. Assateague Island ponies, which live in the wild, offered an untrained comparator group. They studied bones from horses that died or were euthanized for reasons unrelated to a broken or injured third metacarpal bone. Although the size of the third metacarpal bone varied among the 3 breeds, Ms. Goldstein was surprised to find that the bone's strength and structure relative to body size were remarkably similar across the 3 types of horses. “If Thoroughbreds are racing and training around turns, you would expect certain areas of their bones to be a lot stronger to reflect that,” she said. “However, since the Thoroughbred third metacarpals are not more dense or stronger than the other 2 breeds, it indicates that the Thoroughbreds' bones are just not prepared for those forces.” Exposure to the stresses of racing around turns should create anatomical differences between Thoroughbred horses and other breeds. This bone remodeling would prepare their bones to resist fracturing. Ms. Goldstein suggested that adding training around tighter turns at higher speeds could give Thoroughbred horses' bones time to adapt to the extreme forces and be more resistant to breaks on the track. Scientifically backed interventions in how racehorses are managed and trained could better protect them from stress-related breakdowns on the track. MeV
For more information: Goldstein DM, Engiles JB, Rezabek GB, et al. Locomotion on the edge: Structural properties of the third metacarpal in Thoroughbred and Quarter Horse racehorses and feral Assateague Island ponies. Anat Rec. 2020 DOI: 10.1002/ar.24485. https://anatomypubs.onlinelibrary.wiley.com/doi/full/10.1002/ar.24485
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Shutterstock/Yulia She
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What’s the Best Cool-Down After Exercise? The key to cooling down an overheated horse is a long cold shower. Researchers in Japan compared 5 methods for cooling horses after a workout in nearly 90° heat and high humidity—a potentially perilous combination for equids. The animals were exercised until their body temperature, as measured at the pulmonary artery, had climbed to 42° C (107.6° F). Using hot walking as the standard, they looked at other cool-down methods, including walking past B y 10
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A d a m
electric fans, walking with the periodic administration of cold water (10° C; 50° F)—with and without scraping—and a long shower in 26° C water (78.8° F). They found the cold shower was the most effective method and hot walking was the least efficient method of bringing the animals’ core temperature down to below 39° C (102.2° F). The use of fans, and occasionally water, were modestly faster, but didn’t differ significantly from each other, according to the researchers. Andrew Dart, BVSc, PhD, DACVS, DECVS, the
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director of the Research and Clinical Training Unit at the University of Sydney in Australia—who was not involved in the study–said it had important implications for managing horses with Exertional Heat Illness (EHI) and other heat-related symptoms. “The importance of this syndrome is that it is really not in the mainstream equine literature and is poorly understood, studied, documented and is a significant welfare issue in thoroughbred racing in countries where the climate is hot and/or humid,” Dr. Dart told Modern Equine Vet. EHI differs from heat exhaustion in key ways, Dr. Dart said. “In the heat exhaustion syndromes in eventing and endurance horses, horses perform at submaximal exercise over distance, therefore in an aerobic capacity with dehydration and electrolyte imbalance becoming the driving factors leading to poor circulation,” he said. “In EHI, horses exercise in a largely anaerobic capacity: at maximal exercise intensity, over short distance. The rapid production of energy associated with the intensity of work results in a rapid increase in body temperature that overwhelms the thermoregulatory mechanisms.” Horses with EHI may quickly develop clinical signs of heat illness—slow recovery, excessive sweating, irritability and uncooperative behavior—that progress to more serious issues like ataxia, falling,
coma and death. “In many cases the clinical signs are nonspecific and the veterinary teams do not institute the early, aggressive and rapid treatment that needs to be instituted,” Dr. Dart said. “While there are similarities and overlaps in the pathophysiology of EHI and heat exhaustion syndromes the treatment priorities are quite different,” he added. “In EHI, rapid cooling is the key once clinical signs are beginning to present. Of course, better recognition and information [are necessary] around the predisposing environmental conditions. Preventing and managing conditions are vital and in most jurisdictions needs to be based on facts but is currently highly varied, non-specific and ill-informed.” Although showering in the new study appears effective, Dr. Dart noted that it demands large volumes of water. As a result, if it were to be used at events, for example, several stations would be necessary, and some animals might require sedation. “Of course, this is a study and the effectiveness under real conditions would need to be established and may need refinement. However, I do not see any downside of moving this forward,” he said. “This is a nice study, and one that is really about ensuring the importance of EHI as a welfare issue for the racing industry world-wide and how simple and effective prevention could be.” MeV
For more information: Takahashi Y, et al. A Comparison of Five Cooling Methods in Hot and Humid Environments in Thoroughbred Horses. J Equine Vet Sci. 2020 Aug;91:103130. doi: 10.1016/j.jevs.2020.103130. Epub 2020 May 22. https://pubmed.ncbi.nlm.nih.gov/32684268/
Resource Available About Cannabis Use in Animals The American Veterinary Medical Association published a comprehensive resource guide to the latest scientific and regulatory information about cannabis-related products for animals. “Veterinarians face a wide variety of challenges and questions when it comes to cannabis and pets,” said Douglas Kratt, DVM, the president of the AVMA. “This resource guide, compiled by experts from within veterinary medicine and outside of it, will help clinicians get the answers they need,” Dr. Kratt said, adding that with the research and regulatory landscape evolving rapidly, the report will be updated regularly. Information in “Cannabis in Veterinary Medicine” includes: • An introduction to the endogenous endocannabinoid system • A synopsis of manufacturing quality 12
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• A review of animal clinical studies exploring efficacy and safety • Information about potential adverse effects (including data around exposures and toxicoses 3. from poison control centers) •A description of the current regulatory landscape The use of CBD-rich hemp and other cannabinoids is exploding with little evidence for efficacy in animals or even if they absorb these “interesting molecules,” said Joe Wakshlag, DVM, a professor of clinical nutrition and sports medicine and rehabilitation at Cornell University College of Veterinary Medicine, during a session about their use at the recent AVMA convention. The cannabis resource guide is available to AVMA members at https://www.avma.org/system/files/2020-08/ Cannabis-in-veterinary-medicine-AVMA.pdf. MeV
Bill to Protect Racehorses Controversial The Horseracing Integrity and Safety Act of 2020 (S. 4547) recently introduced into the Senate is almost as controversial as the actions that lead to its proposal. The racing industry recently was hit by a rash of fatal breakdowns and a series of doping scandals. Several top trainers were charged with using performance-enhancing drugs on their horses, most notably, Jason Service, whose horse Maximum Security finished first in the 2019 Derby. Maximum Security was later disqualified. The HISA will improve the integrity and safety of Thoroughbred racing by requiring uniform safety and performance standards, including an anti-doping and medication-control program and a racetrack safety program to be developed and enforced by an independent Horseracing Integrity and Safety Authority, according to National Thoroughbred Racing Association (NTRA), which supports the bill. But others, including the American Quarter Horse and the U.S. Trotting Associations, oppose the bill. Their concern is that HISA is directed toward the
Thoroughbred industry and does not include Standardbreds, Quarter Horses and other breeds. In addition, the new bill eliminates the race-day use of furosemide, which can be abused, but also can be used legitimately to mitigate the occurrence of exercise-induced pulmonary hemorrhage in racehorses. “Uniformity of therapeutic medication rules in United States horse racing is a goal long endorsed by the AAEP, and we are eager to evaluate the newly proposed Horseracing Integrity and Safety Act to understand how the legislation will address both antidoping and therapeutic medication control,” said Jeff Berk, DVM, racing committee chair of the American Association of Equine Practitioners. “These 2 pillars require oversight by individuals with a high level of expertise. “It is more important than ever that the AAEP work together with industry stakeholders to create a workable legislative vehicle that will achieve the uniformity, safety and integrity standards we all seek for MeV racehorses and the racing industry.”
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An experimental vaccine against Streptococ-
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cus equi provides at least partial protection against strangles, particularly in animals that receive multiple injections over time, a new study shows. Researchers in Sweden and the United Kingdom who tested the Strangvac vaccine, from Intervacc, said the intramuscular agent protected 31% of ponies that received 1 dose, and 94% of ponies that received 3 doses over roughly a 4-month period. The data from the study are part of the submission package for approval from the European Medicines Agency for marketing of the shot, according to the researchers, who published their findings in a recent issue of the journal Vaccine. Strangles is a significant problem for horse owners
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and the most serious bacterial illness for equines. The infection, which is reportable to health agencies in the United States and some other countries, passes easily between animals and is known to lurk silently in the guttural pouches and sinuses of animals that have recovered from an acute boutâ&#x20AC;&#x201D;representing a reservoir of potential transmission. Younger horses are considered to be more vulnerable to acute illness than older animals, according to a 2018 consensus statement from the American College of Veterinary Internal Medicine (J Vet Intern Med 2018;32:633â&#x20AC;&#x201C;647). For the new study, Jan-Ingmar Flock, PhD, a professor in the Department of Microbiology, Tumour and Cellbiology at the Karolinska Institute, in Stockholm, and a co-founder of the pharmaceutical company Intervacc AB, and his colleagues evaluated 4 dosing schedules of the recombinant-fused-protein vaccine in 56 ponies, ranging in age from 6 months to 1 year. For comparison, the researchers also included groups of horses that received placebo injections. All of the treated animals received 2 rounds of injections, 1 at Day 0 of the study and another at Day 28. Sub-groups of ponies received additional shots at Day 119, Day 210 and Day 392 of the trial, which marked the 52-week point after the second injection. Optimal protection was observed in the group that received 3 doses of the vaccine over a 119-day period, followed by a challenge of S. equi 2 weeks later. In that group, 15 of 16 ponies (94%; P<0.0001) were protected from the infection, the researchers reported.
“These data provide evidence that the administration of a third vaccination at up to 52 weeks post second vaccination induced antibody responses in sera and nasal secretions that were equivalent to those obtained following the second vaccination. Therefore, immune memory cells—which were induced following the primary course of 2 vaccinations— persisted for at least a period of 1 year,” they wrote. Although maximum protection was achieved with repeated doses of the vaccine over a 119-day period, Dr. Flock said that this should not be a problem for horse owners. “It is very common that a vaccine is given at several occasions to obtain a good protection. Another example is vaccination against equine influenza, where at least 3 doses should be given and
a revaccination at least once per year,” he said. There are at least 2 other vaccines for strangles available in the United States and Europe, but Dr. Flock said the new vaccine has at least 1 critical advantage over the available vaccines: It produces immune reactions that can be differentiated from those sparked by infection with S. equi. It is important to be able to distinguish between natural infection and a horse that was vaccinated on a blood test, he told Modern Equine Vet. “This is particularly important during an outbreak. None of the strangles vaccines on the market have this possibility.” MeV The study was funded by Intervacc.
For more information: Robinson C, et al. Intramuscular vaccination with Strangvac is safe and induces protection against equine strangles caused by Streptococcus equi. Vaccine. 2020;38(31):4861-4868. https://www.sciencedirect.com/science/article/pii/S0264410X20306915?via%3Dihub
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TECHNICIAN UPDATE
Tachycardia Under Anesthesia— A Reaction to Potassium G Penicillin Joyce Guthrie, RVT On June 3, 2019, Barbie, a 15-month-old Quarter Horse mare was referred to the University of Missouri Veterinary Health Center, (MU-VHC), with a history of an unresolved colic. The mare had a history of colic approximately 2 months prior, which had been treated and resolved on the farm by the referring veterinarian with the nonsteroidal anti-inflammatory, flunuxin meglamine and hand walking. The current episode began on June 1, 2019 with signs of inappetence and rolling on the ground indicative of abdominal pain. As with the prior episode, Barbie had been treated by the referring veterinarian using flunixin meglumine and hand walking. Although there was some improvement and restoration of appetite, further signs of abdominal pain (including rolling on the ground) were evident by the next day. The mare was further treated with IV fluids and flunixin meglumine. Additional diagnostic tests undertaken by the referring veterinarian on the morning of June 3 included abdominocentesis, complete blood count (CBC) and abdominal ultrasonography. The peritoneal fluid appeared clear and yellow, a normal finding. Identified abnormalities included mild leukocytosis and abnormal small intestine. The mare was subsequently referred to MU-VHC for emergency treatment of colic. Upon arrival at MU-VHC, the mare exhibited ongoing signs of pain, and she tried to lie down and roll in the parking lot. The mare presented in adequate physical condition (BCS 4/9), weight 261 kg, rectal temperature 99.6° F (99.5° F–101.5° F), heart rate 64 bpm (28–44 bpm), respiratory rate 24 brpm (11–24 brpm). Ongoing signs of abdominal pain included continual attempts to collapse and roll. To facilitate further diagnostic testing, xylazine hydrochloride was administered on an as-needed basis over the course of the next 90 minutes. The mare’s mucous membranes were dark pink and moist, but the capillary refill time was <2 sec (a normal finding). Other abnormalities noted on physical examination included decreased borborygmi throughout all 4 quadrants and the presence of tympany in the dorsal aspect of the right flank. Following aseptic catheter placement in the left jugular vein, additional diagnostic tests included routine bloodwork (CBC, plasma biochemical profile, blood lactate and serum amyloid-A [SAA] concentra16
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tions), per rectum-abdominal palpation, passage of a nasogastric tube (for evaluation of reflux), and abdominal ultrasonography. Significant findings included absence of reflux, cloudy appearance to peritoneal fluid with neutrophilia 41,440/uL (<5,000/uL) 82% non-degenerated neutrophils and 18% macrophages, which sometimes displayed leukophagia. This was indicative of some degree of peritonitis and significant inflammation. Laboratory test results included an elevated SAA concentration (308 ug/mL, reference range <20 ug/mL) and normal lactate concentrations in both blood and peritoneal fluid. Ultrasonography revealed some dilated loops of small intestine in inappropriate locations, but with peristalsis present. There appeared to be a consolidated area of overlapping intestines or a small intestinal loop that was within the cecal lumen— this was not a repeatable finding—indicative of intussusception or severe inflammatory bowel disease. On abdominal palpation-per rectum, there was a small colon impaction that felt very hard and firm, and distended loops of small intestine. It was noted that the “impaction” was unusually hard and large. A foreign body was a potential differential diagnosis. Due to the intermittent colic, the age of the mare, peritoneal fluid analysis, findings on ultrasonography and abdominal palpation, the differentials were intussusception, small colon impaction—possibly a foreign body—and gastrointestinal disease leading to adhesions. were differential diagnosis. The findings were discussed with the owner, who agreed to an exploratory celiotomy.
Anesthesia
Barbie was walked to the anesthesia induction area where her mouth was rinsed and her feet cleaned. She was moved into the induction stall and sedated using xylazine hydrochloride 1.1 mg/kg (280 mg, IV). Following sedation, she was induced for general anesthesia with midazolam 0.033 mg/kg (8.5 mg, IV) and ketamine hydrochloride 2.5 mg/kg (700 mg, IV). The ketamine dosage was increased (normal dose 2.2 mg/ kg) due to a reduction in the midazolam dose (normal dose 0.066). Midazolam causes muscle relaxation with resultant respiratory depression. To avoid this effect, the midazolam dose was reduced by one-half. The mare was then intubated with a 22 mm endotracheal (ET) tube and mechanically lifted into the surgery suite where she was placed in dorsal recumbency. An ET tube cuff was inflated and used while the horse was connected to the anesthesia machine. For the first
2 hours of the procedure she was maintained using 2% isoflurane in 100% oxygen at a rate of 5 L/min. Subsequently, isoflurane administration was reduced to 1.5% for the remaining 2 hours of the procedure. Throughout the anesthetic period, the mare’s eyes were protected from dehydration by topical administration of an ophthalmic lubricant. Warmed lactated Ringer’s solution was administered to maintain euvolemia (20 mL/kg/hr for the first 2 hours and 10 mL/kg/hr for the remainder of the procedure). Routine, intra-procedural monitoring included electrocardiography, employment of an arterial catheter (aseptically placed in the facial artery) for invasive blood pressure monitoring and arterial blood gas analysis. Blood gas analysis on healthy horses, or when normal values are resultant, would be routinely monitored at hourly intervals. If results warrant, they may be monitored more frequently. Other parameters that were monitored while under anesthesia; heart rate, pulse quality, respiratory rate and character, eye position, palpebral reflex, nystagmus, mucous membrane color and capillary refill. An anesthesiologist directly observed treatment form
designed for these parameters was employed. During placement of the arterial catheter it was evident that the pulse was weak (difficult to palpate). This could have been due to vasodilation and hypotension caused by the pre-anesthesia and induction drugs administered, and the addition of isoflurane. Therefore, ephedrine (25 mg, IV) was administered 5 minutes after placement of the patient on the surgery table. Ephedrine is a vasopressor that stimulates the alpha-1 adrenergic receptors causing vasoconstriction and a resultant increase in blood pressure. Ephedrine is administered as a bolus, which can be accomplished quickly and easily. Ephedrine’s effects generally persist for 20–30 minutes, by which time a 2% lidocaine hydrochloride constant rate infusion (CRI) had been started and the isoflurane administration rate had been reduced. Dobutamine hydrochloride is another vasopressor that might have been considered at this time, but it is administered as a CRI and must be given to effect. Dobutamine hydrochloride is a positive inotrope and stimulates the beta-1 adrenergic agonist receptors to increase the strength of the myocardial contraction.
TECHNICIAN UPDATE
ventilation was initiated at 6 brpm and tidal volume (Vt) at 3 L. Follow-up evaluation 30 minutes later indicated that acidosis had improved (PaCO2 47.8 mmHg, pH 7.28, HCO3 22.4 mmol/L, B.E. 4.2 mmol/L PaO2 422.9 mmHg). Throughout the anesthetic period, Barbie’s heart rate fluctuated consistently between 40 and 50 bpm. The surgical diagnosis was a linear foreign body in the lumen of the small intestine. Pieces of a rope-like material were maneuvered into the transverse and proximal small colon to be exteriorized through several enterotomy sites. Although some minor spikes in HR and blood pressure coincided with some of the surgical manipulations, the HR never exceeded 58 bpm. Two hours into the surgical procedure the opioid butorphanol tartrate (6 mg, 0.6 mL, IV) was administered for pain in response to one such spike and the HR remained below 50 bpm until the incident reported as follows: IV Flunixin meglumine and penicillin G potassium were requested to be administered by the surgeon. Flunixin meglumine was administered first and the IV line was flushed using heparinized saline. Penicillin G potassium (K-pen) was administered slowly (over 5 minutes). The HR increased suddenly from 49 bpm to 80 bpm during K-pen administration. Over the next 5 minutes HR continued to increase to 100 bpm. This time point coincided with the closure of the abdominal incision. It seemed unlikely for the tachycardia to be associated with surgical manipulation. I will note here that on the initial biochemistry panel the mare’s potassium was 3.3 mEq/L (2.7–4.4 mEq/L). Potassium was also normal (3.42 mmol/L) on the initial blood
Figure 1: The day she went home.
Figure 2: Two months post-op
Photos courtesy of the owner.
Dobutamine hydrochloride takes longer to adjust to the proper dosage for the given situation, ephedrine was deemed the better choice. Following placement of the arterial catheter the mean arterial pressure (MAP) was 79 mmHg, and quickly declined to 65 mmHg over the next 15 minutes. Without establishing and maintaining adequate blood pressure (MAP 70-75 mmHg) proper tissue and organ perfusion could not be maintained. A dobutamine hydrochloride CRI (1 mg/mL, 1.5 drops/3 sec, IV) was administered and adjusted to as needed to maintain the MAP between 70–75 mmHg. Concurrently a 2% lidocaine hydrochloride CRI was initiated with a loading dose (340 mg, 17 mL, IV, followed by 784 mg, 39 mL/hr IV). Lidocaine hydrochloride promotes balanced anesthesia by providing visceral analgesia, anti-inflammatory properties and acts as an anti-arrhythmic, thus allowing rate of administration of the isoflurane to be reduced-assisting with maintenance of normal blood pressure. Results of arterial blood gas analysis undertaken within 15 minutes of the start of the surgical procedure were within acceptable limits. Results of subsequent blood gas analysis 50 minutes later was also within acceptable limits, although there was evidence of incipient arterial hypercarbia (62.8 mmHg, normal range is 35–45 mmHg). Satisfactory arterial oxygen tension (PaO2 351.2 mmHg-on 100% oxygen, respiratory rate 8 brpm) indicated that the mare was oxygenating well. Therefore, adjustments to the anesthetic protocol were not made at that time. Unacceptable respiratory acidosis/hypercarbia was identified one hour later. (PaCO2 76.3 mmHg, pH 7.174, HCO3 28.4 mmol/L, B.E. –1.7 mmol/L, PaO2 374.1 mmHg). Therefore, mechanical
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gas evaluation and continued to remain within normal parameters, actually decreasing, (2.86 mmol/L) on subsequent blood gas analysis. The mare was also on LRS, which contains potassium, for the duration of the anesthetic period. An HYPP-positive horse would have been prone to an episode due to stress brought on by colic and or anesthesia, resulting in an increase in potassium. Therefore, I ruled out HYPP as a cause for the tachycardia. There was no nystagmus, no spike in blood pressure, no movement, and no sign that the mare was waking up prematurely from anesthesia. Two treatments with ketamine hydrochloride (100 mg, 1 mL, IV) were therefore administered (5 minutes apart) as a precautionary measure (to prevent premature arousal). The issue was still unresolved and the heart rate continued to rise, now 115 bpm. I consulted with a board-certified veterinary anesthesiologist, discussing the possibility that the tachycardia was the result of iatrogenic hyperkalemia due to the IV administration of the K-pen. It was noted the most common side effect of potassium administration is lowering of the HR (relative bradycardia). Tachycardia had been documented previously on cases here at MU-VHC. (I have observed tachycardia associated with K-pen administration on 2 cases with awake standing horses, in hospital within the last 5 years.) The anesthesiologist advised giving 0.05 mL/0.5 mg phenylephrine IV. This is an alpha1 adrenergic-agonist and a vasopressor. The reason for giving this vasopressor was to cause vasoconstriction and reflex bradycardia—the HR should decrease. At this time the HR was 120 bpm. Following consultation, phenylephrine (0.05 mL/0.5 mg IV) was administered 4.5 hours from the beginning of anesthesia. Within seconds the HR began to decline and decreased to 60 bpm. 10 minutes later the HR had increased to 110 bpm. Therefore, a second dose of phenylephrine (0.05 mL/0.5 mg IV) was administered. The HR decreased quickly to 60 bpm. Uneventful post-anesthetic recovery was facilitated by the use of a demand valve. The mare was extubated 30 minutes after having been placed in the recovery stall. Prior to extubation, it was necessary to spray the vasoconstrictive agent oxymetazoline (5 mL), into both nasal passages due to nasal passage congestion. The mare’s anesthetic recovery was in other respects, routine and uneventful.
Figure 3: 1 year post-op.
Post-op
Following return to a stall, treatment of the mare included administration of 2% lidocaine hydrochloride (as a CRI, dosed as above), polymyxin B (5000 IU/kg, IV, BID), heparin (50 IU/kg, SQ, TID), metronidazole (15 mg/kg PO, BID), flunixin meglumine (1.1 mg/kg, IV, BID). Fluid administration was continued (LRS 1 L/hr, IV). Broad spectrum antibiotic treatment was afforded with-ceftiofur sodium (2.2 mg/kg, IV, BID) and gentamicin sulfate (6.6 mg/kg, IV, SID) for the first portion of her post-op recovery. After the incident with tachycardia under anesthesia, it was decided that K-pen was not the antibiotic for Barbie! Barbie was in the hospital for 24 days before being released to go home. Her post-recovery was relatively uneventful, especially considering that she had consumed what appeared to be a rope halter and lead rope, which had to be removed in sections from several enterotomy sites. Although the prognosis for a successful outcome was initially rather unfavorable, a year later, she has been started under saddle and is doing very well. MeV
About the Author
Joyce Guthrie RVT, is an Equine Anesthesia and Surgery Technician at the University of Missouri College of Veterinary Medicine, Veterinary Health Center, in Columbia, Mo.
For more information: Rowland S. Blood Pressure Management in Equine Anesthesia. In Veterinary Technician. Vetlearn.com 2013 Mudge M. Intravenous Lidocaine for Controlling Pain and Inflammation, Article, AAEP Convention Dec. 1–5, 2007, Orlando, FL. Reprinted in The Horse March 23, 2008. ModernEquineVet.com | Issue 9/2020
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