Emily HaggettBVSc, DACVIM, MRCVS, RCVSRecognised Specialist in EquineInternal Medicine.

Emily is a member of theinternal medicine team atRossdales Equine Hospitaland has a particular interestin equine neonatology.Emily joined Rossdales in2009 and her main role isworking within theNeonatal Intensive CareUnit, in addition to workingwithin the internal medicinedepartment.In 2012, she became anRCVS Specialist in EquineMedicine (InternalMedicine), having beenawarded recognisedspecialist status by theRoyal College of VeterinarySurgeons (RCVS).Emily is also a Diplomate ofthe American College ofVeterinary InternalMedicine, which sheachieved during 3 years atthe University of California'sVeterinary Medical TeachingHospital at Davis prior tojoining Rossdales. She has completed anumber of research projectsrelated to neonatal foalconditions and haspublished and lecturedwidely on the subject

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aking a blood samplefor analysis in thelaboratory is one ofthe most common

diagnostic procedures carriedout in equine practice. Vets useresults of blood tests to helpdiagnose a huge range ofconditions. Sometimes we willalso use a blood test to reassureourselves that there is nounderlying illness or disease.However, for a horse owner theresults of a blood test can be quiteconfusing; they are not alwaysblack and white and sometimeswe identify things that aren’tnecessarily related to the initialproblem.

Taking a blood testTaking a blood test is usually asimple procedure (Figure 1). Mostblood samples are collected fromthe jugular vein in the neck - alarge vein with a diameter of 3-4cm. For most tests, 10-20mls ofblood is sufficient. Alert your vet ifyour horse (or you!) is afraid ofneedles! The blood is collectedinto specific tubes to allow fordifferent types of analysis (Figure2). Some tubes contain anti-coagulant to stop the blood fromclotting which allows the redblood cells to be analysed in thelaboratory. Some tubes containspecific factors to speed upclotting to allow the componentsof blood (red blood cells andserum) to be separated from eachother for analysis. Once blood iscollected it needs to be taken to alaboratory for analysis. Many vetswill have basic analysis equipment

within their practice. Manyspecialist tests will need to be sentto a laboratory. It is very importantthat a laboratory that specialisesin analysis of equine samples isused to get reliable results (Figure 3).

HaematologyHaematology is the analysis of thecellular component of the blood.This basically involves analysis ofthe red and white blood cells. Areduced number of red blood cellsin a blood sample indicates

anaemia. Red blood cells areessential to carry oxygen aroundthe body and hence severeanaemia can lead to signs ofweakness and depression in ahorse (Figure 4). Milder anaemiais more likely to be associatedwith mild lethargy. The mostcommon cause of anaemia in thehorse is a non-specific response toillness, often called ‘anaemia ofchronic disease’. This canfrequently be seen in horses thathave experienced a recent viralinfection or any other type ofillness. Other causes of anaemiaare bleeding (e.g. in a horse thathas experienced a severe kickinjury and is suffering frominternal bleeding) or haemolysis,which means the breakdown ofred blood cells. This is often quitea serious condition in horses andmost commonly occurs as anautoimmune disease or secondaryto drug reactions or severe illness.When anaemia is identified,

special laboratory testscan be used to helpwork out the underlyingcause. Analysis of the white bloodcells can help identify thepresence of infection in a horse’sblood. A high white blood cellcount (leucocytosis) usuallyindicates a response to infection.This can be a bacterial infection

(for example pneumonia) but canalso occur in response toendoparasites (intestinal worms)or other diseases that causeinflammation without aninfectious cause (e.g. sand colic).There are multiple types of whiteblood cells and analysis of thedifferent sub groups can helpidentify the cause of the problem(Figure 5). Neutrophils are

Blood Disorders in HorsesVET

PROFILE

TVetWa

tchBy Emily Haggett, BVSc, DACVIM, MRCVS, RCVS

Recognised Specialist in Equine Internal Medicine

A blood sample can be collected from the jugular vein in the horse’s neck.

Different coloured blood tubes contain different anti-coagulants and factors to allowspecific laboratory tests to be carried out.

Beaufort Cottage Laboratories is a specialist equine laboratory which offers ahuge range of dedicated equine blood tests.

Pale mucousmembranes can be asign of anaemia in ahorse.

Figure 1

Figure 2

Figure 3

Figure 4

Analysis of a blood smear can help look atthe different cell types in a horse’s blood.These images show a blood smear from anormal horse (left) and a horse withleukaemia (right).

Figure 5

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commonly increased in responseto bacterial infections, eosinophilsin response to allergic reactions orendoparasites and lymphocytes inresponse to viral infection. A very low white blood cell count(leucopenia) can also be a sign ofinfection. This often occurs inresponse to a sudden severeinfection and is seen before thehorse has time to increase theproduction of white blood cells torespond to an infection or otherinflammatory challenge. If yourhorse is unwell and a bloodsample indicates a very low whiteblood cell count then your vetmay wish to carry out more teststo try and identify the source ofthe problem. These might includeultrasound of the chest andabdominal cavities, rectalexamination, collection of aperitoneal fluid sample etc. Primary blood disorders such asleukaemia are identified veryrarely in horses. They are usuallyidentified when an extremely highwhite blood cell count is identifiedon a blood test and analysis of ablood smear shows white bloodcells that are abnormal inappearance.

BiochemistryBiochemistry involves the analysisof serum or plasma, which is theyellow watery part of the bloodthat is left once the red and whiteblood cells have been removed(Figure 6). Biochemistry tests arecommonly used to evaluate thefollowing:

Liver functionCertain enzymes such as gammaglutamyl transferase (GGT) andaspartate aminotransferase (AST)are present in normal liver tissue.When liver tissue is damaged ordiseased, these enzymes arereleased into the bloodstream.The extent of the increase canoften be an indicator of theseverity of the problem. Mildincreases in liver enzymes can beseen quite commonly and areoften not a cause for concern. Bileacids can also be measured inblood. An increased bile acidconcentration is often a sign thatthe function of the liver isreduced.

Kidney functionUrea and creatinineconcentrations can be measuredin blood and are an indicator ofrenal function. Increasedconcentrations indicate that thekidneys are not functioningnormally.

Muscle diseaseAspartate aminotransferase (AST)and creatine kinase (CK) areenzymes present in muscle tissue.When muscle tissue is damaged,these enzymes are released intothe blood and can be detected inhigh concentrations. For example,this occurs in horses that have

‘tied-up’ or in horses that haveatypical myopathy.

Blood proteinsAlbumin and globulin areimportant blood proteins. A lowalbumin concentration can occurfor a number of reasons but ismost commonly a sign ofintestinal disease. Lowconcentrations can be seen inhorses with weight loss that haveinflammatory bowel disease or inhorses with acute diarrhoea.Increased globulin concentrationscan be a sign of inflammation inthe horse.

ElectrolytesMeasurement of bloodelectrolytes (sodium, potassium,chloride, magnesium etc.) isimportant in horses withdiarrhoea or renal disease.

Other testsA huge number of other specifictests are available. These rangefrom endocrine tests to look forhormonal diseases such as EquineCushing’s Disease, to tests thatlook for antibodies to specificdiseases (e.g. Strangles infection).Your vet will select these tests ifthey have specific concerns aboutyour horse.

SummaryBlood analysis in horses canprovide a huge wealth ofinformation about the health ofyour horse. A general blood screenshould help identify any signs of illhealth or infection and identifyany specific problems with organfunction. Sometimes however, ablood test doesn’t give all theanswers and will often need to befollowed up by a furtherinvestigation from your vet.

A biochemistry analyser is used for a variety of tests involving the analysis of serum orplasma

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Figure 6

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