University of Kentucky College of Agriculture, Food & Environment

 

Gluck Center > Equine Disease Quarterly > October 2013

 

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Commentary

Dr. Larry Bramlage has a saying: “For practicing veterinarians, research is the currency in which we trade. Every day we use the information these researchers generate.” The same holds true for farm managers and trainers, or, actually, anyone whose day-to-day routine involves caring for horses.

We should not anticipate that all health issues will someday be solved. However every step along the way to taking better care of horses is a direct result of Dr. Bramlage’s “currency”—research. While an individual farm manager’s innovative horsemanship might provide better care for his/ her horses, every horseman depends on scientific research for improvement.

Veterinary research generally follows the path of knowledge developed in a laboratory or other experimental setting, then published in a peer-reviewed scientific journal. Ideally, it is then ready to be applied at the farm/stable level, likely first by veterinarians whose routine requires a good deal of scientific reading.

If we zero in on horse farms specifically, the following are a few illustrations of how research at universities has moved the needle forward. Many practices of today might seem like second nature, or just good logic, but actually were the product of research and its resultant conclusions. The practice of placing mares under lights to promote estrus was the result of research carried out at the University of Kentucky, for example. Tests for common diseases such as equine herpesvirus (EHV) infection, influenza, botulism, equine protozoal myeloencephalitis, and leptospirosis are other examples of research aiding the farm manager. Would a farm manager have been able to devise them himself, without the work of skilled researchers?

Research also has the potential to alert even the most conscientious veterinarian or horseman that some part of his/her “knowledge” needs be put aside and replaced with new information. A case in point was brought to memory with the recent passing of the remarkable veterinarian Michelle LeBlanc. It was not many years ago that she reported after a research project on placentitis that, “Clinicians, myself included, had thought that the mare aborts because the uterus begins to contract prematurely. So, we tended to place the mare on many drugs that likely did nothing to stop the progression of the disease and may actually have harmed the mare.” The best and the brightest were pursuing what they thought was in order, and it took more research to set them straight.

Knowledge does not have to be complete in order to be useful. We certainly cannot say that research has come up with all the answers needed to deal with EHV-1. Yet, when an outbreak threatened the cutting horse industry a couple of years ago, those grappling with it turned to ongoing research. Dr. Jerry Black was on that battlefield and afterward remarked that, “knowledge we had of the virus and how to manage the outbreak came from many projects.”

Support for ongoing research truly is money in the bank.

CONTACT:
Mr. Edward L. Bowen
(859) 224-2850, ebowen@jockeyclub.com
President, Grayson-Jockey Club Research Foundation, Inc.
Lexington, Kentucky

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Second Quarter 2013*

The International Collating Center, Newmarket, United Kingdom, and other sources reported the following disease outbreaks.

Contagious equine metritis (CEM) was reported from Germany and the USA. The former diagnosed the disease on five premises. Three stallions and five mares (non-Thoroughbreds) were confirmed positive for Taylorella equigenitalis on culture and polymerase chain reaction (PCR). Of three infected Warmblood mares imported into Kentucky, USA, earlier in 2013, one gave birth to a healthy foal during the period under review that was culture negative for CEM. A 2-year-old Thoroughbred filly in Florida was confirmed positive for T. equigenitalis prior to export to Puerto Rico. Intensive investigation into the filly’s background has failed to identify the source of infection.

Strangles was confirmed in Denmark (six horses on a premises), France (four outbreaks), Sweden (one outbreak) and the USA (endemic with outbreaks in numerous states including Kentucky, Maine, Texas and Wyoming).

Equine influenza was reported from Sweden (two outbreaks of single cases), the UK (seven cases on one premises) and the USA (sporadic cases in at least 10 states).

Equine arteritis virus was isolated from the semen of a carrier stallion in Germany.

Equine herpesvirus-1 and -4 related diseases were recorded by Argentina, France, Germany, Japan, the UK and the USA. Equine herpesvirus-1 (EHV-1) respiratory disease was confirmed in France (two outbreaks), Germany (one outbreak), the UK (one outbreak) and the USA (outbreaks in Florida and Kentucky). Abortion caused by EHV- 1 was reported from Argentina (two cases on one premises), France (single cases on five premises), Germany (four cases on three premises), Japan (14 cases in Thoroughbreds on seven premises), the UK (a single case), and the USA (single cases on two premises). EHV-1 neurologic disease was recorded in France (single case), the UK (single case), and the USA (outbreaks in New Jersey and New York, the latter involving four cases at a harness track).

Equine herpesvirus-4 was associated with outbreaks of respiratory disease in Argentina (outbreaks on two premises involving 13 Thoroughbred foals), and France (12 outbreaks). France also reported a single case of abortion due to the virus.

The USA recorded several cases of infection with equine herpesvirus-2 in Florida and Kentucky and numerous cases of equine herpesvirus-5 infection.

Equine infectious anemia was reported from the USA, with 12 cases on a premises in Nebraska and one case in Texas.

Reports of equine piroplasmosis were received from France (endemic, sporadic clinical cases), and the USA (19 cases of Theileria equi infection on six premises in southeastern Texas).

Outbreaks of salmonellosis were reported by the USA involving Group B and Groups C1 and C2 salmonellae. The USA also recorded cases of Equine Monocytic Ehrlichiosis in Florida (two) and Kentucky (seven). Rotavirus was confirmed in France (five outbreaks) and Germany (one case). Clostridial enteritis was diagnosed in foals in several states in the USA. The USA also recorded a limited number of cases of enteropathy due to Lawsonia intracellularis.

Leptospiral abortion was reported from Argentina (five cases on one premises). Isolated cases of nocardioform placentitis and abortion were confirmed in Kentucky, USA.

Individual cases of Hendra virus infection were diagnosed on two premises in Queensland, Australia.

The USA reported nine cases of Eastern Equine Encephalomyelitis involving Florida, Georgia and South Carolina, and single cases of West Nile Virus encephalitis in Ohio and Texas. Rabies was confirmed in the United Arab Emirates (two cases in non-Thoroughbreds) and the USA (two cases on separate premises).

Germany recorded a case of Anaplasma phagocytophilum infection in a Warmblood mare. Rhodococcal disease was stated to be endemic in the USA, with only a percentage of outbreaks being reported.

*First Quarter Report for Australia

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Dying Ash Trees and Wildfire Threat

Horse owners recognize that fire prevention is critical on the farm, but may overlook threats from insect infestation on surrounding trees. The emerald ash borer (EAB), Agrilus planipennis Fairmaire, is a beetle first discovered in 2002 in Michigan and Windsor, Ontario and has killed ash trees by the tens of millions in North America. According to the US Department of Agriculture, Animal and Plant Health Inspection Service, the beetle has been confirmed in 20 states as of August 5, 2013 (see map). While the threat of wildfires is unfortunately common in the western US, states with EAB infestation may have an ever increasing threat of larger wildfires.

US map of Emerald Ash Borer Detections

*Adapted from http://www.aphis.usda.gov/ plant_health/plant_pest_info/emerald_ash_b/ downloads/NewCountyDetectionMap2013.pdf

The EAB has no natural predators and the use of insecticides is expensive and has variable results, depending on the product. As a result, the continued threat of this pest moving across the country is very real. During the EAB lifecycle, the adult beetle will feed on the foliage of the ash tree and lay eggs on the bark of the tree. The resulting larvae hatch from the eggs and then bore into the bark of the tree where they remain until spring feeding on the critical inner bark, thus interfering with the tree’s ability to utilize nutrients and water. This ultimately leads to the death of the tree. In the spring the adults emerge from the tree and fly a short distance to continue the life cycle.

The dead ash trees resulting from EAB infestation constitute a potential fire hazard, and should be removed from farms to protect horses and property. Check with a Cooperative Extension Agent on the legal ways to dispose of trees, as transporting them to a secondary location can also spread the pest. Fire risk increases during times of drought and when abundant fuel sources are available, such as the case when dead trees and shrubs are present.

How to protect your horses from fire.In an effort to mitigate the hazard of wildfire on the farm, owners should establish a defensible space by removing flammable vegetation from around houses, barns, machinery and horses. The incorporation of fuel breaks, strategic grazing and landscaping with non-combustible materials and fire resistive plants can help reduce the risk from disaster (see Sidebar).

Fire can spread by hot embers dispersing to new fuel sources including buildings, hay, bedding and manure. Research from the Institute for Business and Home Safety and others has indicated that buildings located less than 15 feet apart are particularly vulnerable to this type of fire spread. Proper planning of new construction including the use of fire resident materials can reduce this threat.

The likelihood of a wildfire increases dramatically when the fire danger is moderate to high combined with a large number of dead trees in forested areas. As the devastating 2013 US summer wildfires have so dramatically shown, wildfires can be started by lightning strikes, humans (deliberately or accidentally) and sparks from vehicles and machinery. Having a plan and implementing fire prevention practices are critical to limiting losses of human and animal life, buildings and land.

CONTACT:
Dr. Melissa Newman
(859) 257-5881, melissa.newman@uky.edu
Department of Animal and Food Sciences
University of Kentucky, Lexington, Kentucky

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Equine Monocytic Ehrlichiosis: Kentucky Case Series, January 2008-August 2013

Equine monocytic ehrlichiosis (EME) is also known as Potomac Horse Fever (PHF) and equine ehrlichial colitis. The disease has since been reported in most states in the US, at least three Canadian provinces and also in parts of South America, Europe and India. The disease usually occurs near rivers, lakes and wet pastures from mid- to late-summer.

The cause of EME is Neorickettsia risticii, formerly Ehrlichia risticii. The reservoir for the causal agent is not clear but it has been isolated from ticks, aquatic insects, flukes and other helminths. Snails act as an intermediate host in the fluke cycle. Horses are thought to be infected through the ingestion of insects, often mayflies, which may land in drinking water. Experimentally, the incubation period ranged from 1-3 weeks in horses.

In the early stage of the infection, horses may become anorexic, depressed, pyrexic and have decreased gut sounds. This is usually followed by loose stools or watery diarrhea and colic. In the late stages of the disease, affected animals may have severe dehydration, ventral abdominal edema, and laminitis. Death is the consequence of cardiovascular compromise and toxemia. Case fatality rates range from 5-30%. Transplacental transmission is reported often leading to fetal resorption, abortion, or weak foals. Horse-to-horse transmission is not thought to occur.

Horses that recover from the disease may have protective immunity for up to two years. Available vaccines appear to have variable efficacy. Limiting proximity of horses to rivers, ponds, lakes and low-lying pastures during the peak EME season and eliminating lighting at night in horse stables to minimize attraction of insects may reduce the risk of infection.

A provisional clinical diagnosis of EME needs to be confirmed by a veterinary laboratory competent in diagnosing the disease. A single positive indirect fluorescent antibody (IFA) test result for EME on serum only indicates exposure to the agent. Paired blood samples collected two weeks apart demonstrating a four-fold or greater rise in titer is evidence of an active infection. In clinical cases, a polymerase chain reaction (PCR) assay should be performed on an EDTA blood sample as well as on a fecal sample, as presence of the causal organism in blood and feces may not temporally coincide. At necropsy, a scraping of the colonic mucosa is the specimen of choice for PCR testing for EME.

From January 2008 through August 2013, the University of Kentucky Veterinary Diagnostic Laboratory had 123 equine samples submitted that tested positive for EME by PCR. Included in this number were 26 horses submitted for necropsy that were diagnosed with EME. Of the necropsy cases, the sex distribution was 53% female and 47% male. The mean age distribution was 8.7 years (range 0.3-34 years). The breeds involved were mostly Thoroughbred.

Chart of EME PCR Positives

CONTACT:
Dr. Craig Carter
(859) 257-8283, craig.carter@uky.edu

Dr. Jacqueline Smith
jacqueline.smith2@uky.edu

Dr. Erdal Erol
erdal.erol@uky.edu
Veterinary Diagnostic Laboratory

University of Kentucky, Lexington, Kentucky

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The Importance of Nutrition in Enhancing Immunity in the Aging Horse

Over the past century, improvements in health care and advancements in biology, chemistry and medicine have extended the average lifespan of humans and companion animals, including horses. However, we are now facing new challenges with the paradox of an older population with increased longevity, while confronted with the potential for many years of poor health. A better understanding of the mechanisms leading to a decline in physiologic function with age would provide new predictive biomarkers and potential therapeutic targets.

It has been well-documented that the aged, including horses, have increased susceptibility to and prolonged recovery from infectious diseases, poor responses to vaccination, and increased incidence of various cancers. Furthermore, it is now accepted that chronic inflammation (inflamm-aging) is a major underlying condition of many age-related diseases, such as atherosclerosis, arthritis, cancer, diabetes, osteoporosis, dementia, vascular diseases, obesity and metabolic syndrome.

In anti-aging research, much attention is focused on nutritional interventions as practical, cost-effective approaches to mitigating this agerelated breakdown in immune function. These natural dietary compounds found in a variety of fruits, vegetables, nuts and seeds are promising candidates in helping to combat the effects of aging. They possess broad biological activities: anti-oxidative, anti-inflammatory, detoxification, regulating signaling pathway, and modulation of enzyme activities (see Table 1).

Table 1Since aged horses (>20 years) have increased levels of inflammation, and treatment with longterm use of non-steroidal anti-inflammatory drugs (NSAIDs) such as flunixin meglumine and phenylbutazone can pose health problems, we are interested in nutritional interventions to counteract this inflamm-aging process.

Flavonoid (quercetin) and polyphenolic compounds (curcuminoids, resveratrol, pterostilbene and hydroxypterostilbene) were compared to phenylbutazone and flunixin meglumine to determine differences in equine cytokine production in cell culture. White blood cells from aged horses were isolated and incubated overnight with each compound or NSAID at multiple concentrations. Inflammation production was measured when cells were stimulated.

At varying doses (measured in micromolar units [μM]), each of the compounds and NSAIDs significantly reduced cellular inflammation: curcuminoids (20 μM), hydroxypterostilbene (40 μM), pterostilbene (80 μM), quercetin (160 μM), resveratrol (160 μM), flunixin meglumine (40 μM) and phenylbutazone (>320 μM). Interestingly, curcuminoids at a concentration of 20 μM reduced inflammation to the same level as higher doses of flunixin meglumine (40 μM) and phenylbutazone (>320 μM). All natural compounds outperformed phenylbutazone by being effective at lower doses.

This preliminary research has led into two studies using aged horses to determine: 1) if a relationship exists between circulating vitamin and fatty acid levels to systemic inflammation and muscle mass, and 2) if anti-inflammatory supplementation affects immune responses to vaccination. These are preliminary steps to identify effective nutritional intervention regimens to improve function of the immune system in the aged horse.

CONTACT:
Dr. Amanda Adams
(859) 218-1097, amanda.adams@uky.edu
Maxwell H. Gluck Equine Research Center
University of Kentucky, Lexington, Kentucky

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Selenium Status in Horses

Selenium (Se) plays a role in the antioxidant mechanism of the body, and has also been shown to affect the immune system in many species. Additionally, Se is incorporated into at least 25 different selenoproteins. The synthesis of these selenoproteins depends on the availability of Se within the body. Herbivores rely on plants to meet their Se requirements, while plants obtain Se from the soil. However, soil Se concentration varies geographically, resulting in inconsistent dietary Se intakes across regions in grazing animals.

Areas that tend to be low or marginal in Se include parts of the Eastern United States, New Zealand, Northeastern China, Europe, Egypt and South Africa. Horses kept in low Se areas, or exclusively fed forage and unsupplemented grains produced in low Se areas, may become Se deficient over time.

Central Kentucky is known to be marginal in Se. Therefore, the long term effects of dietary Se intake on the Se status, immune function and exercise response of the horse was studied at the University of Kentucky in collaboration with the Alltech–UK Nutrigenomics Alliance.

Horses grazing low Se pastures were fed a Se-free supplement for 28 weeks. Then, over the next 28 weeks, a third of these horses was supplemented with 0.3 mg Se/kg dry matter and a third received the same amount of Se, but as sodium selenite. The remaining horses stayed on the unsupplemented diet. Throughout the study a fourth group of horses was given a supplement providing the National Research Council’s recommended Se intake of 1 mg Se/day for a 500 kg horse (approximately 0.1 mg Se/kg dry matter).

The study results demonstrated that the Se status of horses kept in a low Se area, without additional Se supplementation, declined over time. At the end of the initial 28 week depletion, blood Se concentration was 165 ng/mL and glutathione peroxidase (GPx) activity was 43.1 enzymatic units/g hemoglobin (EU/g hb), compared to reference values for horses of adequate Se status of 180- 240 ng Se/mL and 40-160 EU/g hb, respectively. A selenoprotein, GPx is regarded as a hallmark indicator of Se status.

Following Se supplementation, low Se status was corrected within 60 days. In unsupplemented horses, both blood Se and GPx continued to decrease to 125 ng Se/mL and 33.8 EU/g hb, respectively. Immune function assessment of the horses indicated that low Se status was detrimental to the immune system.

Also, following exercise the horses of low Se status experienced a decrease in GPx activity which did not recover within 24 h post-exercise. This decrease occurred even though the exercise was mild, designed with the recreational riding horse in mind. GPx activity increased post-exercise in horses supplemented with Se-yeast, but decreased in the inorganic Se group. Because of its antioxidant role, a decrease in GPx post-exercise could leave horses vulnerable to oxidative stress.

Overall, dietary Se intake should receive special consideration for horses kept in low Se areas, especially if they are kept on pasture with minimal supplementation. Commercial feeds and supplements often contain additional Se, so all feeds (pasture, hay, concentrates and supplements) should be considered when estimating dietary Se. Although Se deficiency may pose risks for horses, Se toxicity can also occur, so over-supplementation should be avoided.

CONTACT:
Dr. Laurie Lawrence
(859) 257-7509, llawrenc@uky.edu
Department of Animal & Food Sciences
University of Kentucky, Lexington, Kentucky

Dr. Mieke Brummer
mbrummer@alltech.com
Alltech, Inc.
Nicholasville Kentucky

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Editors:
Roberta Dwyer
Peter Timoney
Neil Williams
Staff:
Diane Furry
Tawana Brown
Dennis Duross

Correspondence should be addressed to the editors,
Department of Veterinary Science, Gluck Equine Research Center,
University of Kentucky, Lexington, KY 40546-0099;
Phone (859) 257-4757; FAX (859) 257-8542.

 

Maxwell H.Gluck Equine Research Center
Department of Veterinary Science, University of Kentucky
Lexington, Kentucky 40546-0099

Main Office (859) 257-4757
Fax (859) 257-8542