VTNE Review: Common Horse Diseases

valvular disease

• common in foals (congenital) and in mature horses (degenerative or infectious)

• diseased valves may either impede normal flow (stenosis) or allow backflow (insufficiency) which increases the workload of the heart and decreases cardiac output

• common causes include endocarditis and ruptured chordae tendinae

clinical signs of vascular disease

• murmur

• increasing exercise intolerance

• ± fever (with endocarditis)

• ± weight loss

• ± intermittent lameness

• ± arrhythmias

• development of CHF

• sudden death

diagnosis of valvular disease

• clinical findings

• ECG

• ECHO with doppler study

• exercise testing

• if endocarditis

  • anemia

  • decreased blood protein

  • leukocytosis

  • positive blood cultures

• holter monitoring

treatment of valvular disease

depends on severity of symptoms and location of the lesion

degenerative valve disease

• usually results in valvular insufficiency or a leaky valve

• with every contraction, blood is pumped forward out of the ventricles, but much of the chamber volume is also pumped backward into the atria

• increases the volume in the chambers for the next contraction (preload)

• as the chambers become overstretched, they must work harder until they begin to fail

treatment of degenerative valve disease

manage the development of CHF and cardiac arrhythmias

• furosemide (oral)

• digoxin (1-2 times daily orally)

• ACE inhibitor: 2 times daily (avoid use in pregnant mares)

bacterial endocarditis

• inflammatory disease of the lining tissue of the heart

• most common location for lesions is on the left AV valve or on the left side of the endocardium

• jet lesions from mitral insufficiency or ventricular septal defects typically damage the endothelial lining of the heart

• circulating bacteria begin to colonize the damaged area, attracting inflammatory cells, and the cellular debris begins to build up at the site

• cardiac output decreases, creating a shock-like syndrome

treatment of bacterial endocarditis

• IV antibiotic therapy based on culture and sensitivity results for 4 to 8 weeks

• potassium penicillin every 6 hours

• Gentamicin once daily

• extremely guarded prognosis in most cases

ruptured chordae tendinae

• clinical symptoms depend on the number ruptured

• tearing of the chordate will result in a flapping of the valve leaflet and produce a valvular insufficiency

• greater the number of chordates torn, the worse the leakage of the valve

• horse may develop CHF

• these horses should not be ridden

clinical signs of ruptured chordae tendineae

• increasing exercise intolerance

• lethargy

• auscultation of murmur

• possible sudden death

diagnosis of ruptured chordae tendineae

• serum chemistries

• ECG

• ECHO

treatment of ruptured chordae tendineae

• supportive care

• as valvular insufficiency worsens, treatment for CHF may be needed

vascular disease

• these include thrombophlebitis from catheter placement of IV injections, parasitic thromboemboli in the mesenteric arteries and vascular rupture

clinical signs of thrombophlebitis

heat, pain, swelling at site over vein, fever

clinical signs of parasitic thromboemboli

recurrent signs of colic

clinical signs of vascular rupture

sudden death

diagnosis of vascular disease

• CBC: neutrophilic leukocytosis

• ECHO: abnorma

• culture and sensitivity of infected site

• history of poor deworming practices (colics)

• necropsy (vascular rupture)

treatment of vascular disease

• broad spectrum antibiotics

• NSAIDs

• surgically remove the obstruction; may include vascular grafting

• no general treatment for parasitic thromboemboli

thrombophlebitis

• inflammation of the lining of a vein with the formation of clots

• often seen in the jugular vein from improper catheter maintenance or other vascular trauma

treatment of thrombophlebitis

• high doses of broad spectrum antibiotics or antibiotics based on culture and sensitivity results

• hot compresses over the site of inflammation

• surgical resection of the vein if medical treatment is unsuccessful

atrial arrhythmias

• fairly common in the horse

• atrial tachycardia, atrial flutter, and atrial fibrillation are the most likely causes of clinical disease

what arrhythmia is commonly seen in horses at rest?

second degree AV block

clinical signs of atrial arrhythmia

• auscultation os a rapid, abnormal heart rhythm

• history of poor or declining performance

• exercise intolerance

• ± pulmonary hemorrhage

• ± respiratory distress

• CHF

• ataxia, collapse, or both

diagnosis of atrial arrhythmia

• CBC and serum chemistries: may indicate hypokalemia

• radiography: usually normal

• ECG

• Echo: usually normal unless underlying cardiac disease is present

treatment of atrial arrhythmias

• provide drug therapy for conversion to normal rhythm:

  • Quinidine sulfate: oral every 2 hours until conversion or until toxicity develops

  • digoxin: given concurrently if resting heart rate is more than 90 to 100 bpm or conversion cannot be achieved with Quinidine alone

• electrocardioversion

• consider resting the horse for 1 to 2 weeks after conversion, although racing horses may return to training within 48 hours of conversion

uneven tooth wear

• common dental abnormalities that need attention:

  • sharp enamel points on the lingual and buccal surfaces

  • sharp hooks that protrude downward from the first or last tooth of the upper arcade

  • sharp ramps that protrude upward from the first or last tooth of the lower arcade

  • wave mouth

  • step mouth that results from a lack of wear of one tooth, allowing it to grow excessively long

  • retained wold teeth

clinical signs of uneven tooth wear

• bit avoidance

• quidding (dropping small, chewed bits of hay)

• poor performance

• undigested feed in feces

• weight loss

• prolonged eating time

choke

• refers to a condition in which partial or total obstruction of the esophagus occurs, usually caused by feed impaction

• often have a history of bolting their feed

• may also occur if fed too quickly after sedation

clinical signs of choke

• difficulty swallowing

• excessive salivation

• swelling of the throat

• discharge of food from the nostrils

• neck extension

differential diagnosis for choke

• dysphagia

• cleft palate

• dental problems

• oral foreign body

diagnosis of choke

• may be obtained by palpation of the esophagus and passage ( or lack thereof) of the NG tube

• radiography

treatment of choke

• lavage with gallons of warm water through the NG tube

• perform esophageal massage

• provide IV fluid therapy

• severe cases may need general anesthesia

• antibiotics given

• NSAIDs given to reduce esophageal inflammation

gastric ulcers

• horses that have an empty stomach for longer than 6 hours at a time are more prone

• feeding concentrate meals predisposes a horse to ulcers by lack of saliva production and constant secretion of HCl acid in the stomach

• NSAIDs can cause ulcers in the stomach and the right dorsal colon

clinical signs of gastric ulcers

• chronic, low grade colic

• anemia, if they are severe and chronic

• loss of condition and decreased endurance

• some horses may show discomfort when saddled

diagnosis of gastric ulcers

endoscopic examination of the stomach

treatment of gastric ulcers

• medication and management changes

• omeprazole is very effective

• letting horse graze as many hours as possible; feeding small, frequent meals; increasing the amount of forage and decreasing the amount of concentrate fed

colic

• many causes

• gut sounds may be absent or hyperactive

impaction colic

• anatomy of a horse’s gut predisposes it to impactions especially in these areas:

  • ileocecal junction

  • pelvic flexure

  • diaphragmatic flexure

• can be caused by a variety of factors:

  • sand, may accumulate in the cecum

  • enteroliths

  • feed

  • dietary indiscretion, when a horse ingests objects such as a baling twine, rubber, wood, etc

gas or spasmodic colic

• often caused by grain overload when bacteria ferment the concentrate and produce gas

• typically extremely painful but often resolve spontaneously

• pain appears to be intermittent

displacement or entrapment colic

• occurs when a portion of the GI tract moves out of normal positioning and may become trapped by another structure

• inguinal hernias and nephrosplenic entrapments are examples

infectious or inflammatory colic

• occurs as a result of the pain of inflammation of structures in the abdominal cavity

• examples: peritonitis and anterior enteritis

necrotic colic

• occurs because of lack of blood supply to an area of the intestine

• portion of the intestine then dies and feed does not pass through

• in the past, major cause was migration of strongyle larvae which cause damage to the intestinal lining resulting in blood clots that may break off and occlude the blood supply to the intestine

clinical signs of colic

• pawing

• rolling

• lying down more than normal

• sweating

• kicking at abdomen

• looking at sides

• tachycardia

diagnosis of colic

• clinical signs

• gray to brick red mucous membranes; poor CRT

• increased PCV

treatment of colic

• prevent horse from rolling which may cause displacement and torsion

• pain relief: Buscpan; Flunixin meglumine; Xylazine

• administer NG tube:

  • water

  • electrolyes

  • mineral oil to help relive impaction

  • psyllium, especially in sand colic

• dipyrone: injectable for fever and pain

• IV fluids

• surgery in severe cases

large strongyles

• three species that affect horses:

  • Strongylus vulgaris

  • Strongylus edentatus

  • Strongylus equinus

• most pathogenical of all intestinal parasites

• disease caused by migration of worms, causing inflammation in blood vessels and leading to formation of clots; clots may occlude the vessels, resulting in lack of blood supply to the area and causing local tissue death

• effective dewormers: pyrantel, ivermectin, moxidectin, and fenbendazole

life cycle of large strongyles

• adults attach themselves to cecum and colon and lay eggs

• eggs hatch and larvae crawl in the grass

• horse ingests and swallows larvae

• larvae migrate through vessels and gut wall

• prepatent period is 6 to 12 months

small strongyes

• also known as cyathostomes

• more than 50 species affect horses

• direct damage to the gut wall, impairing digestion and absorption

• effective dewormers: pyrantel, ivermectin, moxidectin, fenbendazole

life cycle of small strongyles

• adults in colon lay eggs

• eggs hatch; infective larvae are consumed by horse

• larvae invade the wall of the cecum and large colon

• larvae form cysts in the walls of the gut for 1 to 2 months

• larvae emerge and mature into adults

threadworms

• Strongyloides westeri

• problems mainly in foals

• ingestion of larvae in mare’s milk

• implicated in foal heat diarrhea

• some immunity by 12 to 16 weeks of age; infections minimal

• effective dewormer: pyrantel, ivermectin, moxidectin, fenbendazole

roundworms

• Parascaris equorum

• most common in foals, clinically irrelevant in horses older than 2 years of age

• intestinal blockage

• worms actually use the nutrients instead of the horse

• may cause intussusception

• effective dewormers: pyrantel, ivermectin, moxidectin, fenbendazole

life cycle of threadworms

• adults lay eggs in the small intestine

• larvae are ingested by the horse

• larvae migrate

life cycle of roundworms

• adults live in small intestine and lay eggs

• foals ingest embryonated eggs

• liver and lung migration

pinworms

• oxyuris equi

• mostly from irritation of the perinuem; horse itches and rubs tail head

• effective dewormers: pyrantel, ivermectin, moxidectin, fenbendazole

life cycle of pinworms

• adults live in large and small colon

• female parasites migrate to the anus, rupture, and spew eggs into the environment

• infective eggs are ingested; larvae hatch and migrate

tapeworms

• Anoplocephala perfoliata; Anoplocephala magna

• previously little clinical disease attributed to tapeworms; with newer effective dewormers, competing parasite populations are removed and tapeworms are able to flourish

• effective dewormer: praziquantel

bots

• Gastrophilus spp

• usually does not cause oo many problmes

• may cause ulceration, perforation, peritonitis

• effective dewormer: ivermectin, after. the first hard frost

life cycle of tapeworms

• horse ingests the mite

• larvae are released from the mite and attach themselves to the cecum and small intestine

• adults release proglottids into the environment

• proglottids release the eggs which are consumed by mites

life cycle of bots

• adult fly lays eggs on the horse

• horse licks the eggs and ingests larvae

• larvae migrate through the oral cavity and tongue

• bots are located in the stomach

salmonellosis

• may affect horses of all ages, but it is mostly seen in young horses

• causative agent is Salmonella spp

• organism is present in most horses but it usually causes disease only when the animal is immunocompromised such as in times of stress

• illness is caused by a toxin that the bacteria release

clinical signs of salmonellosis

• profuse, foul smelling often bloody diarrhea

• may become septic

  • inappetance, depression

  • fever

  • abdominal pain

  • increased heart and respiratory rates

  • injected sclera

  • dehydration

treatment of salmonellosis

• correction of IV fluid loss; IV fluids with electrolytes, then oral fluids through NG tube

• antiserum

• NSAIDs

• diarrhea control

• ± antibiotics

• probiotics

clostridial infections

• similar to salmonellosis but much more severe

• animals often ie before the onset of diarrhea

• most often seen in foals

• caused by Clostridium perfringens type A

• bacteria release a toxin that erodes the gut wall

clinical signs of clostridial infections

• profound depression and inappetance

• severe pain

• injected sclera

• shock with:

  • pale mucous membranes

  • rapid heart rate

  • weak, thready pulse

• fever

• profuse bloody diarrhea

treatment of clostridial infections

• IV fluid therapy

• pain control (Banamine, Ketoprofen, Xylazine)

• peniciilin

ehrlichiosis (potomac horse fever)

• more commonly found in horses living near large waterways and is also commonly seen in the summer months

• caused by Neorickettsia risticii

• involves a fluke and it also appears to involve insects that feed on the secretions of snails and flukes

• disease causes inflammation of the colon, impaired water absorption, and diarrhea

clinical signs of potomac horse fever

• fever, depression

• mild abdominal pain

• slowed gut movements

• diarrhea

• some horses experience toxic signs

• laminitis is a common sequel

treatment of potomac horse fever

• oxytetracycline

• maintenance of hydration, possibly IV fluid therapy

• banamine to prevent laminitis

which parasite has historically been considered the most pathogenical of all equine parasites?

strongylus spp.

one of the most common causes of explosive diarrhea in stressed, hospitalized horses is what?

Salmonella

one possible consequence of feeding horses soon after sedation or anesthesia. iswhat?

choke

what might predispose a horse to gastric ulcers?

• chronic administration of NSAIDs

• intense training

• high concentrate diets

it is recommended that all horses have their teeth examined and floated how often?

at least yearly

long term use of NSAIDs may result in what?

gastric ulceration

where are you most likely to fnid roundworms?

a nursing foal

which parasite may result in damage to the tail of the horse?

oxyuris equi