New Test


Download Report

Ontario Animal Health Network (OAHN)
Equine Expert Network
Quarterly Veterinary Report

Ontario Animal Health Network - equine logo

OAHN Q4 Survey: Key Results

Overall survey responses were decreased for this quarter so changes from the previous quarter are difficult to interpret. One case of endocarditis was reported with no causative agent identified. Exacerbations of equine asthma were reported early in the quarter and some cases of inflammatory airway disease were difficult to control . Sporadic cases of Strangles were noted as well one horse was reported to have a reaction to the rabies vaccine suffering from colic, recumbency and hives. Pruritic skin diseases were reported. High fevers were noted after the yearling sales in the fall and some horses developed secondary bacterial infections.

Network Member Reports

Northern Region
(Drew Hunnisett)

Cases of colic, namely impactions and displacements occurred with normal frequency for the time of year. Impactions occurred during a cold spell in mid to late November especially. The number of horses with recurrent airway obstruction were typical but a few did not respond to corticosteroid therapy as they typically do. Some cases had septic inflammation on BAL. One horse with suppurative bronchopneumonia didn’t survive. That horse had been treated with dexamethasone for July and August and presented in October for fever and dyspnea. A number of horses were diagnosed with laminitis this quarter. The very dry summer followed by rain in September and October caused an increase in grass growth likely tipping susceptible horses over the edge. Diarrhea with no other clinical signs was also diagnosed in some horses. Most resolved without treatment and no etiologic agent was identified. One horse with acute fever died 48 hours later with pulmonary hemorrhage likely secondary to DIC.

Southwestern Region
(Melissa McKee)

There was an increased number of horses with colic, namely impactions and displacements this quarter, with routine presentations. There was an uptick in exertional rhabdomyolysis cases in standardbred racehorses and performance horses likely due to management changes (not decreasing feed) when confined during bad weather. There were a number of refractory equine asthma cases, in part, related to a lack of access to quality forage. Cases of EOTRH (equine odontoclastic tooth resorption hypercementosis) were diagnosed. There was a single case of Strangles which occurred this quarter. Respiratory outbreaks occurred in Standardbred yearlings but no etiologic agent was identified. Hoof abscess occurred related to the type of footing, and there were fewer seasonal laminitis cases which may be due to an increased awareness of PPID/IR amongst owners. A slight increase in cervical vertebral malformation cases was noted and a number of horses were tested for EPM and Lyme disease but no positives were reported. One gypsy vanner horse was diagnosed with leg mites.

Eastern Ontario
(John Donovan)

During the quarter, about two horses a week were diagnosed with colic, namely spasmodic and impaction colic, the latter likely related to poor forage quality or lack of water. A couple of surgical colic cases were euthanized. Over the Christmas holidays, several aging ponies with previous histories of laminitis had exacerbations of the condition. A horse with significant dyspnea and tachypnea was diagnosed with a S. zooepidemicus pulmonary infection. Guttural pouch mycosis was diagnosed in a horse that presented with epistaxis (dribbling) of over a week. The owner had assumed it was due to trauma. The coil procedure was performed at Ste. Hyacinthe and was successful. The horse also developed seizures. It is not clear whether they were related to trauma or fungal invasion. An MRI of the brain was normal. A severe case of exertional rhabdomyolysis with renal changes was successfully treated.

Ontario Veterinary College
(Memo Arroyo)

The number of horses admitted with colic was typical. A horse with urine dribbling and fever was diagnosed with sabulous cystitis and, at post mortem, had abscessation of the bladder wall with intestinal and body wall adhesions. Horses with colitis, a foal with patent urachus and abortions due to umbilical torsions and congenital defects ( one with only one umbilical artery and a distended liver) were diagnosed. A QH with lung consolidation involving a 10×10 cm area was diagnosed and Bordetella, Bacteroides and Peptostreptococcus sp.were cultured from a biopsy. The horse was initially placed on penicillin, gentamicin and metronidazole and then switched to chloramphenicol. The mass reduced to 1×0.5 cm in size when the antibiotics were discontinued.

AHL Pathology
(Murray Hazlett)

  • 2 yo G with colitis , diarrhea and weight loss had marked myocardial fibrosis and degeneration with multifocal myopathy. Vit E/Se was normal. Ionophore or plant toxicity were considered.
  • 5 yo G with a high fever and diarrhea, that was treated with oxytetracycline for Potomac Horse Fever, had severe enteritis with cryptal dysplasia typical of coronavirus or parvovirus in other species. Testing was negative.
  • 12 yo G with chronic weight loss had a severe gastric impaction with severe idiopathic gastric mural fibrosis. Cause unknown.
  • 6 month old colt diagnosed with Lawsonia intracellularis infection presented for severe colic had chronic, severe multifocal ulceration with a fibronecrotic membrane.
  • 17 yo stallion with acute colic, had a hard multilobulated mass felt rectally. Microscopically this mass had Splendore-Hoeppli reaction (crystallization around bacterial colonies typical of certain bacteria). Actinomyces sp was identified with mixed anaerobes. The mass was 30x30x40 cm in size and adherent to the left kidney.
  • 14 yo mare with chronic colic and heaves had a lymphocytic bronchitis with severe chronic ulcerative and eosinophilic colitis, consistent with eosinophilic enteritis.
  • 2 yo filly was tranquilized for radiographs and had a reaction to the detomidine (increased breathing, shivering, sweating) and died later that day. A cerebrovascular infarct was diagnosed possibly due to trauma.

(Alison Moore)

11 WNV equine cases and 2 WNV alpaca cases were diagnosed for 2018. In Q4, a farm in Middlesex County dealt with an influenza outbreak. Unvaccinated horses had high fevers and nasal discharge. Vaccinated horses were only mildly affected.

Laboratory data – Highlights for Q4


The number of fecal tests performed for 2018 was similar to that in 2017 (2036 vs 2053) with similar number of tests performed in Q4 (377 in 2018 vs 360 in 2017). The percentage of egg counts greater than 500 epg was fairly similar for Q4 between McMaster and Wisconsin tests (15.5% and 14.4% respectively) . Year over year there has been an increase in the number of tests performed for equine protozoal myelitis (EPM) (102 in 2018, 89 in 2017) but the number of positive tests has remained about the same (37 in 2018, 40 in 2017).

Nutrients (normal range: selenium 0.12 – 0.18 ppm, vitamin E 4.6 – 23 umol/L)

The percentage of blood samples tested for selenium concentration that were below 0.12 ppm was higher this quarter at 43.8% of submitted samples compared to 29.8% of samples in Q4 of 2017. Overall the percentage of samples <0.12 ppm for 2018 was slightly higher (41.2%) than in 2017 (35.6%). The percentage of blood samples tested for vitamin E concentrations that were below 4.6 umol/L decreased this quarter to 40% of submitted samples compared to 61.4% of samples in Q4 2017. Overall, however, the percentage of samples below 4.6 in 2018 (58%) was similar to that of 2017 (52%).

Microbiology (AHL tests only)

The number of total cultures performed in 2018 (1916) continued to increase from 2017 (1115). Similarly in Q4 2018, the number of cultures performed were significantly greater at 501 than in Q4 of 2017 (301). There were notable increases in the number of Staphylococcus (other than aureus) reported compared to Q4 2017. For the year, the two notable increases in bacterial species cultured were Klebsiella oxytoca or pneumoniae at 60 identifications for 2018 versus 19 for 2017 and Staphylococcus (other than aureus) at 153 for 2018 versus 61 for 2017.

The number of tests submitted for Lyme disease (Borrelia burgdorferi) was similar for 2018 and 2017 ( 100 vs 91 respectively). The percentage of positive tests for 2018 were down slightly at 27% versus 36% in 2017.

There were more horses tested by Strangles (S. equi) PCR in 2018 (258) than 2017 (173) but the percentage of positive tests were similar ( 9% in 2018 vs 8% in 2017). There were 6 positive test results in Q4 2018 versus 5 positive test results in Q4 2017.

In 2018, there were more tests submitted for Potomac Horse Fever (Neorickettsi risticii) than in 2017 (179 vs 120) however this was likely due, in part, to active recruitment for the OAHN Potomac Horse Fever project. Twelve percent of the samples were positive in 2018 compared to 22% in 2017. There were no positive tests for PHF in Q4 2017 or 2018.

There were 11 of 22 tests positive for Lawsonia intracellularis in 2018 compared to 7 of 15 tests positive in 2017. Seven tests were positive in Q4 2018.

There were 77 tests submitted for coronavirus testing in 2018 compared to 18 in 2017. Eighteen tests were positive in 2018, mainly in Q1 and Q2, whereas there were no positive tests in Q4.

Postmortem Examinations

The number of post-mortem examinations performed in Q4 2018 was similar to 2017 with 123 being performed compared to 117 in 2017 Q4. Overall there were 560 exams performed in 2018 compared to 513 in 2017. There were 14 submissions from AGCO in Q4, similar to 15 in 2017. The total number of AGCO exams in 2018 was 51 compared to 62 in 2017. The number of cervical stenosis/myelopathy cases was increased at 20 in 2018 versus 7 in 2017. There was a slight increase in gastrointestinal diagnoses in 2018 mainly due to enteritis/typhlitis/colitis cases and gastrointestinal accidents, two of which were diaphragmatic hernias. One horse had squamous cell carcinoma of the bladder.

Case Report – Salmonellosis in a Clydesdale mare

Dr. Sam Molson, McKee-Pownall Equine Services

An 8 year old Clydesdale mare from Wellington County, was initially examined on December 4th for difficulty advancing the right front limb. She was up-to-date on deworming and core vaccinations and she was not on any medications at the time of presentation. On initial examination, she was quiet, alert, responsive with fever (39.5 °C) and pale mucous membranes. She was able to bear weight on the right front limb but demonstrated significant difficulty advancing this limb with a grade 3/5 right front lameness present. Her right antebrachium was mildly edematous and sensitive to palpation. No other significant findings were noted on exam. Survey radiographs of this region were unremarkable and bloodwork showed moderate leukocytosis with band neutrophilia and monocytosis. The mare was initially treated with flunixin meglumine, dexamethasone, trimethoprim sulpha (TMS) and gentamicin in addition to stall rest.

Over the next two days, the mare remained afebrile with normal movement of the right front limb, a good appetite and normal manure consistency. A CBC showed minimal improvement in the leukocytosis. The mare became dull and tachycardic was referred to OVC on December 8th for further evaluation.

On presentation at OVC, the mare was quiet, alert, responsive with mild tachypnea and tachycardia and hypermotile gastrointestinal sounds. Bloodwork showed mild hemoconcentration, hypoproteinemia, hypoalbuminemia andelevated SAA. Transabdominal and transthoracic ultrasound exams and neurologic exam were unremarkable. She remainedcomfortable on intravenous fluids for two days before she developed profuse diarrhea and recurrent fever in addition to poor appetite and significant ventral edema formation. Hypoproteinemia, hypoalbuminemia, hypoglobulinemia and leukocytosis with band neutrophilia were worse. Fecal culture was positive for Salmonella sp. The mare was treated symptomatically with flunixin meglumine, ranitidine, intravenous fluids, psyllium, fecal transfaunation and TMS with no improvement. The mare developed a rectal prolapse on December 25th and an epidural catheter was placed to prevent recurrence.

While in hospital over the next few weeks, the mare was started on low-dose flunixin meglumine and a tapering course of dexamethasone which appeared to improve her appetite and minimize fevers. She was discharged into the care of her owners on December 31st but continued to deteriorate thus euthanasia was elected on January 14th .

Post-mortem examination showed necrotizing and suppurative typhlocolitis with heavy growth of Salmonella (4+) and no other pathogens present. Other notable findings included severe microabscesses secondary to necrosis of the intestinal mucosa and moderate multifocal mucosal cyathostomiasis. Mineralizing and fibrotic nodules were also seen within her liver and were thought to be less significant and most likely indicative of inflammation or previous parasite migration.

Practitioner Pearl

Submitted by Dr. Bob Wright

Removing granulation tissue can be challenging because of its location combined with the use of a sharp object like a scalpel blade. A grapefruit knife with a serrated blade is a great tool for this. It is easy to position flat along the skin and it gives one a bit longer reach for safety. It is also easily cleaned and sterilized.

Diagnostician’s Desk

Laboratory testing for Serum Amyloid A

  • Serum amyloid A is the major acute phase protein in horses.
  • It is produced by the liver in response to inflammation.
  • SAA has .low to undetected amounts in normal horses but increases to 100-1000 times baseline in clinical disease
  • It increases as early as 6 hours after infection or tissue injury.
  • When inflammation resolves, SAA concentration drops within 12 hours.
  • It is stable at room temperature or refrigerated although, according to Cornell University, refrigeration may cause it to degrade more quickly.
  • It can be measured with a stall side test or in the laboratory.
  • It can be measured in plasma or serum.
  • Having a baseline “normal” for an individual when it is healthy can be useful for comparison.

Focus on antimicrobial use/resistance

This practice policy document was developed by the British Equine Veterinary Association as part of their award winning antibiotic use toolkit called PROTECT ME Download it here:

Emerging disease: Pythiosis

After weathering the torrential rain and wind of hurricane Florence in September 2018, the iconic ponies of Virginia’s Chincoteague island faced the hurricane’s aftermath, a new danger called pythiosis. By December, 7 ponies had died from the disease.

Pythiosis (a.k.a. swamp fever or kunkers) is a disease of equids, dogs
and humans caused by the fungus-like organism Pythium insidiosum.
This oomycete, which is phylogenetically closer to algae than true
fungi, is typically found in tropical, subtropical and temperate climates
however it has recently been found in dogs in Wisconsin, New Jersey
and southern Illinois, suggesting its geographical range is expanding.

P. insidiosum is usually identified in wetland conditions, therefore
More cases are seen after heavy rains or floods. The presence of water
is required for the formation of zoospores which are single, nucleated
cells without a cell wall that can swim with the help to two flagella.
The zoospores are what infect the animal by adhesion to hair or
damaged tissue. Zoospores are able to survive in the environment
on decaying plant material. After attachment, the zoospore encysts
on the damaged tissue and forms a hypha that extends into the tissue
and blood vessels. It secretes proteases to weaken the tissue, allowing the hyphae to penetrate. Pythiosis progresses rapidly and can become life threatening if not treated soon enough.

Horses with the cutaneous form, develop pruritic, granulomatous  nodular ulcerative tissue which looks tumour-like. These nodules contain necrotic tissue, eosinophils and P. insidiosum hyphae. Draining fistulas can develop and contain necrotic yellow-grey hard, stone-like material called “kunkers”. Bone may also become infected. Other signs of infection include lameness, lymph node enlargement, anemia and hypoproteinemia. A gastrointestinal form may occur but is rare.

Pythium associated respiratory disease is a condition reported in areas of the US. Horses are reported to have varying degrees of inflammation from a dry cough with clear nasal discharge to cicatrix formation. It is thought that these horses ingest infected grass or hay and the spores cause inflammation of the nose and throat. Immunotherapy appears to be effective for this form of infection.

P. insidiosum antigens trigger a humoral response almost immediately but which does not clear infection. The cellular immunity that leads to cell activation is involved in the extensive tissue damage observed. Degranulated eosinophils and mast cells cause the intense pruritis. The humoral immunity triggers a Th2 response which is maintained by infection and causes the condition to worsen. Horses that have been cured of the disease were able to develop a Th1 mediated immune response.

Differential diagnoses include: habronemiasis, skin fungal infections, extreme granulation tissue or invasive squamous cell carcinoma.

Kunkers, biopsies or scrapings should be sent to a lab as soon as possible in water or saline at room temperature. Refrigeration may inhibit growth. A positive diagnosis is determined by 1) the presence of the agent by wet mount , 2) detection of anti-P. insidiosum antibodies in the serum or 3) PCR of the sample.

Treatment must begun early in the disease as the organism responds poorly to therapy. Wide surgical excision including amputation in dogs and humans is the most widely used treatment. Recurrence (45%) is seen with surgical debridement of skin lesions. Antifungal agents have variable responses with P. insidiosum. Amphotericin B delivered by regional limb perfusion alone or in a 10% DMSO solution has shown some success. Immunotherapy has been the most successful therapy. A vaccine was developed in Costa Rica that cured 72% of affected horses. The success rate is best when given as soon as the disease is diagnosed. The vaccine is thought to switch the Th2 response to a Th1 response. Immunotherapy is usually combined with surgery and antifungal therapy.


Pythiuminsidiosum: an overview.

Gaastra W et al. Vet Microbiol. 2010 Nov 20;146(1-2):1-16.

Cutaneous pythiosis in two dogs from Wisconsin, USA. Oldenhoff W et al. Vet Dermatol. 2014 Feb;25(1):52-e21

Klingler S. Equine Pythiosis: An overview. Today’s Veterinary Nurse. Winter 2018 1(1).

Pan American Veterinary Laboratories. Pythium associated respiratory disease.

Equine research from Ontario and around the world

Plasma transfusions in horses with typhlocolitis/colitis.

Arroyo LG, Sears W, Gomez DE.

Can Vet J. 2019 Feb;60(2):193-196.

Validation of modified radio-frequency identification tag firmware, using an equine population case study.

Milwid RM, O’Sullivan TL, Poljak Z, Laskowski M, Greer AL.

PLoS One. 2019 Jan 9;14(1):e0210148. doi: 10.1371/journal.pone.0210148. eCollection 2019

Comparison of the dynamic networks of four equine boarding and training facilities.

Milwid RM, O’Sullivan TL, Poljak Z, Laskowski M, Greer AL.

Prev Vet Med. 2019 Jan 1;162:84-94. doi: 10.1016/j.prevetmed.2018.11.011. Epub 2018 Nov 26.

Equine Cord Blood Mesenchymal Stromal Cells Have Greater Differentiation and Similar Immunosuppressive Potential to Cord Tissue Mesenchymal Stromal Cells.

Lepage SIM, Lee OJ, Koch TG.

Stem Cells Dev. 2019 Feb 1;28(3):227-237. doi: 10.1089/scd.2018.0135. Epub 2019 Jan 14.

Plasma transfusions in horses with typhlocolitis/colitis.

Arroyo LG, Sears W, Gomez DE.

Can Vet J. 2019 Feb;60(2):193-196.

Validation of modified radio-frequency identification tag firmware, using an equine population case study.

Milwid RM, O’Sullivan TL, Poljak Z, Laskowski M, Greer AL.

PLoS One. 2019 Jan 9;14(1):e0210148. doi: 10.1371/journal.pone.0210148. eCollection 2019

Comparison of the dynamic networks of four equine boarding and training facilities.

Milwid RM, O’Sullivan TL, Poljak Z, Laskowski M, Greer AL.

Prev Vet Med. 2019 Jan 1;162:84-94. doi: 10.1016/j.prevetmed.2018.11.011. Epub 2018 Nov 26.

Equine Cord Blood Mesenchymal Stromal Cells Have Greater Differentiation and Similar Immunosuppressive Potential to Cord Tissue Mesenchymal Stromal Cells.

Lepage SIM, Lee OJ, Koch TG.

Stem Cells Dev. 2019 Feb 1;28(3):227-237. doi: 10.1089/scd.2018.0135. Epub 2019 Jan 14.