Quality of death in fighting bulls; neurobiology of pain and physiological responses

Abstract

During bullfights, bulls undergo physiometabolic responses such as glycolysis, anaerobic reactions, cellular oedema, splenic contraction, and hypovolemic shock. The objective of this review article is to present the current knowledge on the factors that cause stress in fighting bulls during bullfights, including their dying process, by discussing the neurobiology and their physiological responses. The literature shows that biochemical imbalances occur during bullfights, including hypercalcaemia, hypermagnesaemia, hyperphosphataemia, hyperlactataemia, and hyperglycaemia, associated with increased endogenous cortisol and catecholamine levels. Creatine kinase, citrate synthase, and lactate dehydrogenase levels also increase, coupled with decreases in pH, blood bicarbonate levels, excess base, partial oxygen pressure, and oxygen saturation. The intense exercise also causes a marked decrease of glycogen in type I and II muscle fibres that can produce myoglobinuria and muscular necrosis. Other observations suggest the presence of osteochondrosis. The existing information allows us to conclude that during bullfights, bulls face energy and metabolic demands due to the high intensity and duration of the exercise performed, together with muscular injuries, physiological changes, and high enzyme concentrations. In addition, the final stage of the bullfight causes a slow dying process for an animal that is sentient and conscious of its surroundings.

Full text

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Animals2021,11,2820.https://doi.org/10.3390/ani11102820www.mdpi.com/journal/animals
Review
QualityofDeathinFightingBullsduringBullfights:
NeurobiologyandPhysiologicalResponses
DanielMota‐Rojas
1,
*,FabioNapolitano
2
,AnaStrappini
3
,AgustínOrihuela
4,
*,JulioMartínez‐Burnes
5
,
IsmaelHernández‐Ávalos
6
,PatriciaMora‐Medina
6
andAntonioVelarde
7

1
Neurophysiology,BehaviorandAnimalWelfareAssessment,DPAA,XochimilcoCampus,Universidad
AutónomaMetropolitana,CiudaddeMéxico04960,Mexico
2
ScuoladiScienzeAgrarie,Forestali,AlimentariedAmbientali,UniversitàdegliStudidellaBasilicata,
85100Potenza,Italy;fabio.napolitano@unibas.it
3
AnimalScienceInstitute,FacultyofVeterinarySciences,UniversidadAustraldeChile,
Valdivia5090000,Chile;anastrappini@gmail.com
4
FacultaddeCienciasAgropecuarias,UniversidadAutónomadelEstadodeMorelos,
Cuernavaca62209,Mexico
5
AnimalHealthGroup,FacultyofVeterinaryMedicine,UniversidadAutónomadeTamaulipas,
CiudadVictoria87000,Mexico;jmburnes@docentes.uat.edu.mx
6
FacultaddeEstudiosSuperioresCuautitlán,UniversidadNacionalAutónomadeMéxico(UNAM),
StateofMexico54714,Mexico;mvziha@hotmail.com(I.H.‐Á.);mormed2001@yahoo.com.mx(P.M.‐M.)
7
IRTA,AnimalWelfareProgram,VeinatSiesS‐N,17121Monells,Spain;antonio.velarde@irta.cat
*Correspondence:dmota100@yahoo.com.mx(D.M.‐R.);aorihuela@uaem.mx(A.O.)
SimpleSummary:Fightingbullsthatparticipateinbullfightingfaceenergyandmetabolicde‐
mandsduetothehighintensityanddurationoftheexerciseperformed.Undertheseconditions,
specificcorporalmechanisms,suchastheacid–basebalance,areaffected,causingmetabolicacido‐
sis.However,fightingbullsalsoundergomuscularinjuries,physiologicalchanges,andhighen‐
zymeconcentrationsthatreflectthestresstowhichtheyaresubjected,andinsomebulls,bullfights
cantriggerelectrolyticimbalancesthatincludehypercalcaemia,hypermagnesaemia,andhyper‐
phosphataemia,exacerbatedbymuscularnecrosisandmyoglobinuria.
Abstract:Duringbullfights,bullsundergophysiometabolicresponsessuchasglycolysis,anaerobic
reactions,cellularoedema,spleniccontraction,andhypovolemicshock.Theobjectiveofthisreview
articleistopresentthecurrentknowledgeonthefactorsthatcausestressinfightingbullsduring
bullfights,includingtheirdyingprocess,bydiscussingtheneurobiologyandtheirphysiological
responses.Theliteratureshowsthatbiochemicalimbalancesoccurduringbullfights,includinghy‐
percalcaemia,hypermagnesaemia,hyperphosphataemia,hyperlactataemia,andhyperglycaemia,
associatedwithincreasedendogenouscortisolandcatecholaminelevels.Creatinekinase,citrate
synthase,andlactatedehydrogenaselevelsalsoincrease,coupledwithdecreasesinpH,bloodbi‐
carbonatelevels,excessbase,partialoxygenpressure,andoxygensaturation.Theintenseexercise
alsocausesamarkeddecreaseofglycogenintypeIandIImusclefibresthatcanproducemyoglo‐
binuriaandmuscularnecrosis.Otherobservationssuggestthepresenceofosteochondrosis.The
existinginformationallowsustoconcludethatduringbullfights,bullsfaceenergyandmetabolic
demandsduetothehighintensityanddurationoftheexerciseperformed,togetherwithmuscular
injuries,physiologicalchanges,andhighenzymeconcentrations.Inaddition,thefinalstageofthe
bullfightcausesaslowdyingprocessforananimalthatissentientandconsciousofitssurround‐
ings.
Keywords:pain;abattoir;sensitisation;stunning;cattle;animalwelfare;fightingbulls
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Citation:Mota‐Rojas,D.;
Napolitano,F.;Strappini,A.;
Orihuela,A.;Martínez‐Burnes,J.;
Hernández‐Ávalos,I.;Mora‐Medina,
P.;Velarde,A.QualityofDeathin
FightingBullsduringBullfights:
NeurobiologyandPhysiological
Responses.Animals2021,11,2820.
https://doi.org/10.3390/ani11102820
AcademicEditor:ElbertLambooij
Received:13July2021
Accepted:24September2021
Published:27September2021
Publisher’sNote:MDPIstaysneu‐
tralwithregardtojurisdictional
claimsinpublishedmapsandinstitu‐
tionalaffiliations.

Copyright:©2021bytheauthors.Li‐
censeeMDPI,Basel,Switzerland.
Thisarticleisanopenaccessarticle
distributedunderthetermsandcon‐
ditionsoftheCreativeCommonsAt‐
tribution(CCBY)license(http://crea‐
tivecommons.org/licenses/by/4.0/).

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1.Introduction
Fightingbullsareconsideredaspecializedbreedofcattlethathasitsoriginsinthe
speciesBostaurus,whichincludesallbreedsofbovinesinvolvedinvariouszootechnical
practices[1].Aswithalldomesticbovines,certaincriteriaexistintheselectionoffighting
bulls.Since,inthiscase,theobjectiveistobreedanimalsthatwillperformwellduring
bullfights,behaviouralcharacteristicsincalvesandyoungbullsthatmanifestferocity,ag‐
gressiveness,andmobilityareamongthoseconsiderednecessaryforthisspectacle.The
selectionprocessofheifersandyoungbullsinvolvesatestingphase(tientainSpanish),
whileforbulls,itoccursafteranoutstandingperformancewherethebull’slifeisspared
oncethebullfightisover.Onegoalofthesepracticesistoidentifybullsthatwillfight
whenprovokedbyapersonusingsomekindoflure[2].
Duringbullfights,thephysiometabolicresponsescorrespondmainlytothepresence
ofdifferenttypesofstressors,suchasphysical(tissueinjury,pathologies,pain[3]),envi‐
ronmental(extremeweather,microclimate,nutrition,handling[4],transportation[5],
noise[6]),andpsychosocialfactors(socialisolation,overcrowding,pain,fearordistress
[7]).Forfightingbulls,similartoanyothermammal,theresponsedegreeandtheconse‐
quenceintheirhomeostasisdependsonthestressortype,thedurationofthestimulus,
andthepreviousexperiencesoftheanimal[8,9].However,ingeneral,whenanexternal
stimulusisperceivedaspotentiallyharmful,thecentralnervoussystem,throughtheac‐
tivationofthesympathoadrenalandhypothalamic–pituitary–adrenalaxes(Broom,2019)
andthelimbicsystem[7],triggersacascadeofphysiological(i.e.,tachycardia,tachypnea,
hyperthermia),metabolic(hyperglycemia)[9],endocrine(i.e.,stresshormones—catechol‐
aminesorglucocorticoids),andbehavioralresponses.Intheshortterm,thesechanges
serveasanadaptivedefensemechanism.However,whenananimalcannotmaintainits
homeostasisduetotheprocess’schronicityormagnitude,theorganismanditshealth
deterioratealongwithitswelfare[8].Understandingstressresponsesinlivestockcanhelp
refinemanagementproceduresandpromotetheselectionofstress‐tolerantanimals.
Thebullfightisdividedinthreestagescalledtercios:terciodevaras,terciodebanderillas,
andterciodemuleta.Inthefirststage,alanceisstabbedintothebull’shump,limitingits
mobility[10].Theinjuryinflictedbythelancedestroysbloodvesselsandhaemorrhages
thatcandecreasebloodvolumeby8–18%throughperforationsofthetrapezoidand
rhomboidmuscles,andthefunicularportionoftheoccipitalligament.Insomecases,this
injuryalsoaffectstheaccessorynerveandbrachialplexusfromspinalsegmentsC5,C6,
C7,C8,andT1,whichcontrolthemovementofthethoraciclimbs[11,12].Thelancecan
inflictwoundsasdeepas30cm.Ifnotappliedproperly,itcancompromisetheanimal’s
locomotion,asBaronaetal.[10]determinedintheiranalysisofthesite,depth,andsever‐
ityofthelesionsproducedbythisinstrumentafterexamining277fightingbullsfrom43
events.Theysuggestthatthoseinjuriesarelocated,inorderofimportance,inbull’sshoul‐
dersandhump.Ifthelancepenetratesthehindquarters,itcompromisesthebull’sphysi‐
calintegritybycausingpaininthedorso‐lumbarregionthatreducesitsforceoflocomo‐
tion.
Inthesecondstage,thematadorstabssixflags(banderillas)intothebull’sshoulders
and/orhump.Thisactionaggravatesthemuscledamagealreadyinflictedbythelance
becauseeverymovementthebullmakeswhilechargingthematadorandhisredcape
movestheflagsinsidethewounds.Theirsharppointslaceratemusclesindifferentdirec‐
tions,causingadditionalhaemorrhages[10].
Inthethirdstage,thematadorusesaswordtokillthebullbycausingprofusebleed‐
inginthethoraciccavity,eitherbypiercingthepleuratocausepneumothoraxandthe
consequentrespiratoryinsufficiency,orthelungorrightbronchia,allowingbloodtoleave
thelung,enterthebronchia,andreachthetrachea,oesophagus,andupperrespiratory
pathways[13].Inmostcases,theswordalsoseversthespinalcord’slateralnervecords
responsibleforinnervatingthethoraciccavity,producingparalysisandrespiratoryinsuf‐
ficiency.Theswordultimatelycausesasphyxiabyseveringofthemedullaoblongataorits
caudalnervousprojections[14–17].Inthiscase,theswordcutsbloodvessels,thelungs,

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andthebronchia,causingbronchoaspiration[18].Afterthesword,thebullisstabbedwith
apuntilla(shortknife)toendthefight,whichentersnearthefirstandsecondcervicalver‐
tebrae,itwilldamagethemotornerves,causingthebulltofallwithitslimbsextended.If
theinjuryismadeneartheatlantooccipitaljoint,thebulbiscutthespinalcordandits
caudalnerveprojections,possiblyleadingtothesameresult[11].
Thedeathofbullsduringbullfights—whetherbyasphyxiaorexsanguination—oc‐
curswhiletheanimalisfullyconsciousbecausethebrainstemand/orbraincortexremain
intact[17,19].
1.1.StressorsofPsychologicalOrigin
Regardingfightingbulls,studieshavedeterminedthataggressiveness(animal’sca‐
pacitytoconfrontthematadorvs.attemptingtoescape)andferocity(amountofstrength
itusestoattackwithitsentirebody,anditsresistancetopain)havestronggenetic[20]
andenvironment[21]bases.
Thetemperamentoftheanimalcouldbeanotherfactorthataffectsthequalityofits
death.However,studieshavedeterminedthatevenbovineswithharshtemperaments
(Bostaurus,includingfightingbulls)andotherspecieseventuallybecomehabituatedto
novelenvironmentalconditionsandreducetheirbehaviouralreactivity[22].
Thetypicalhandlingpracticesusedwithfightingbullsrequireminimisingorelimi‐
natingcontactwithhumans.Inpartforthisreason,noscientificstudieshaveyetdocu‐
mentedthepeculiaritiesofthisbreedofbulls(Bostaurusbrachyceros)underthesecircum‐
stances,thoughsimilarresultshavebeendeterminedinBosindicussteers[23],horses[24],
andpigs[25,26].Theanatomicalandphysiologicaldifferenceobservedinthefightingbull
havebeendescribedintheconformationofthecerebralhemispheres,inthebrain
weight/carcassweightratio,andinthesizeofthecerebralamygdala,observinganegative
relationshipwithrespecttotheaggressivenessofrace[27].
Ingeneral,acuteseverestressfromphysicaland/orpsychologicalinjuriesinindivid‐
ualscaninduceemotionssuchasfearoranxiety[28].Duringbullfights,factorssuchas
novelty,aggression,andnoise,amongothers,canbestressorsthatcouldtriggerthese
emotions[29].
Whenanimalsareexposedtosituationsthattheycannotcontrolorareunpredictable
(suchasisolation,acutenoise,orconfinement)[30],adaptivehypothalamic,sympathetic,
immune,andbehavioralresponsesservetosurvive[31].Infarmanimals,routinesitua‐
tionssuchashandling,restraining,ortransportareeventsthatcaninducestatesofanxi‐
ety,distress,depression,orfear[32,33].Fearisanegative,subjective,andemotionalex‐
periencederivedfromtherecognitionoranticipationofactualdanger[34].Theamygdala
isthemaincomponentoftheso‐calledfearsystem[32]andisinnatelypresentinmany
domesticspecies.Nonetheless,afearfulanimalisinastateofchronicstresswithitscor‐
respondingproductiveandphysiologicalconsequences[35].Infightingbulls,humancon‐
tactwithanimalsislimited,sometimesuntilthebullenterstheplaza,topreservethefear‐
fulnessandaggressivenesstowardspeople.TheaboveagreeswithDaigleetal.[36],who
mentionsthattemperamentandhuman–animalinteractioninfluencetheperceptionand
adaptationtovariouspsychologicalstressors.Ithasbeenreportedthatthereactionsde‐
rivedfromfearpreservetheintegrityoftheanimalandimproveanimalfitness.However,
aswithanyothernegativementalstate,iffearpersists,theanimalcannotadapttoits
environment,anditswelfareiscompromised[37].
1.2.StressorsofPhysicalOrigin
Oneexampleofastressorofphysicaloriginisfatigueduetotransportorothercauses
ofstrenuousexercise[38],whichresultsinanincreasedbodytemperature,heartandres‐
pirationrates,andactivationofthehypothalamic–pituitary–adrenalaxis[39].Inthephys‐
icalaspect,thereisanincreaseincreatinekinase(CK)activityintheblood,whichisdue
totissuedamageandpoorreperfusionofmuscletissue.Whenperformingphysicalactiv‐
ity,theactivemusclerequiresoxygenandreservesglycogenenergy.However,whenthe

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intensityofphysicalactivityincreases,theoxygendemandalsoincreases,exceedingthe
transportsystem’slevels.Inthisconditiontheactivemuscleuseenergyfromadifferent
source(anaerobic)andtheconcentrationoflacticacidisincreased,which,inturn,devel‐
opsametabolicacidosisthatcanleadtothebreakdownofthemusclefiber.Inaddition,
CKconcentrationincreasesinthebloodsinceitisresponsibleformaintainingenergyho‐
meostasisinsiteswithhighATPcontent.Creatinekinasehasbeenusedasabiomarkerof
physicalstressand/ormuscledamageinanimals[40].Thus,physicalstresspromotesthe
inhibitionofmotorfunctionwhenthelimitofmusculardemandisreached.Therefore,
CKpredominatesinphysicaleffortsofhighintensityandshortduration,suchastrans‐
portationandvigorousexercisethatfightingbullsdevelop.Thiscouldtriggerhighenzy‐
maticactivity.Purroyetal.[41]setouttoidentifypossiblemuscularpathologiesin
fightingbulls,andtodeterminewhethertheyarerelatedtotheweaknesstheyshowas
thebullfightproceeds.Inserumsamplesdrawnaftertheevent,theyidentifiedincreases
intheenzymaticactivityofcreatininekinase,lactatedehydrogenase,andaspartatetrans‐
aminase.Moreover,approximately78%ofthebullssampledinthatstudypresentedsome
histologicallesioninskeletalorcardiacmuscleswithpredominant,chroniclesions[41].
1.3.PhysiologicalResponsestoStressors
Stressresponsesconsistofaseriesofphysiologicalandbehaviouralmechanismsde‐
signedtopromoteadaptationandrestorehomeostasisintheindividual[42],including
physiometabolicchangessuchastachycardia,hypertension,andhyperthermia[43];
changesthataredetectableinanimals’immunologicalandbehaviouralresponses;elec‐
trolyteimbalances;andmoleculardeficienciesthatincreasetheincidenceofoxidative
stress,celldeath,andDNAalterations[44,45].Asoccursinothermammals,thisphysio‐
logicalresponsetostressbeginswithactivationofthehypothalamic–pituitary–adrenal
axis(HPA),whichtriggersmultiplereactionswhenthecentralnervoussystem(CNS)per‐
ceivesapotentialdanger.This,inturn,causesalterationsoftheautonomousnervoussys‐
tem(ANS),andtheneuroendocrinedisordersdescribedabove[46–48].
InBosindicus,excitableBrahmanheifershadsignificantlyhigherserumcortisolcon‐
centrationsthandocileones,whichnegativelyaffectedserumLHconcentrations[49].
Similarly,Curleyetal.[50]foundapositivecorrelationbetweentemperamentandcortisol
values.Theexercisethatfightingbullsperformduringthe15minthatanaveragefight
lasts[51]andthelowaerobicresistancecharacteristicofbullscouldleadtheirmetabolism
towardsananaerobicprocess[52].Inrelationtothis,Escalera‐Valenteetal.[51]observed
thephysiologicalresponseinbloodsamplesdrawnfrom3144–5‐year‐oldfightingbulls
thatdiedafterfightscharacterisedbyintenseexercise.Theyfoundthatsomeresponses
haddecreased(bloodpH,HCO3,BE,PO2,sO2),othersremainedwithinnormalranges
(Na+,K+,iCa,Htc),andtherestincreased(PCO2,Hb,lactate)comparedtonormalrefer‐
encevaluesforotherbovinespecies.Clearly,theseeventscouldtriggermultiplemeta‐
bolicresponsesinfightingbulls,includingdecreasesintheacid–basebalanceandblood
pH[52],asoccursinotheranimalsundersimilarconditions.However,itisimportantto
pointoutthat,duetothehandlingproceduresusedwiththeseanimals,theresearchers
wereunabletodrawsamplesbeforetheeventthatwouldhavepermittedacomparative
analysis[51].ItiswellknownthataggressivebovinessuchasAngus‐crosssteerscanshow
elevatedvaluesofcertainmetabolitesassociatedwithenergycatabolism[22],soitisnec‐
essarytoconductmorestudieswithfightingbullstodeterminewhetherthevaluesre‐
portedbyEscalera‐Valenteetal.[51]couldbeconsiderednormalduetothetemperament
ofthisbreed,regardlessoftheexerciseperformedduringbullfights.


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1.4.BehavioralResponsestoStressors
Animalsmodifytheirbehaviorasadefensemechanismtocopewithoravoidstress‐
ors[53].Thebehavioralchangescanincludeflight,fight,orfreezing,associatedwithan
increaseintheconcentrationofadrenalineorcortisol.Examplesofstressfulstimuliarea
newenvironment,transportation,vibration,noise,anddurationofthetrip[54],aswellas
beingexposedtoadverseweatherconditions[55].
Cattlecanperceivesoundsofmuchhigherfrequenciesthanhumans,andmayper‐
ceivethenoiseinthefightingringasathreat,whichisanotherstressorthatcanaffect
theirbehavior,producingfear[56],especiallyifwhenjoinedwithnoveltyandotherneg‐
ativeexperiences.Otherbehaviorsassociatedwithfearareincreasedeliminationpatterns
[57].
Thevocalizationsoftheanimalscanprovideanimportantsourceofinformation
aboutitsphysicalandpsychologicalcondition[58].Forthisreason,thevocalizationstruc‐
turehasbeenstudiedasanessentialbehavioralindicatoroftheirstresslevel.Low‐inten‐
sityandlower‐pitchedvocalizationshavebeenassociatedwithhighercortisolconcentra‐
tionsunderstressfulevents[59].
1.5.TheAimoftheReview
Inthiscontext,theaimofthisreviewistopresentcurrentknowledgeonthefactors
thatcausestressinfightingbullsduringbullfights,includingtheirdyingprocess,bydis‐
cussingtheneurobiologyandphysiologicalresponsestowhichtheyaresubjected.Dueto
thescarcityofscientificstudiesofthesetopics,comparisonstootherbreedsofcattleare
includedwhereappropriate.
2.NeurobiologyofPain
2.1.PainPerception
Animals’brainsareirrigatedthroughthebasioccipitalplexusandcarotidarteries,
whichsupplybloodprimarilytotheoccipitallobeofthecerebralcortex,andthebasilar
arteriesthatcarrybloodrostrally[60,61].Duringbullfights,bullsaresubjectedtoinjuries
becausethelance(puya)andflags(banderillas)arestabbedintotheirbodies,damaging
skin,muscles,arteries,veins,andconnectivetissue,allofwhichcontainphysiological
sensorscallednociceptors.Thesesensorsgenerateelectricalimpulsesthatsendsignalsto
thecentralnervoussystem,wherecattlecoulddetectthemaspain[60,62,63].Thissensory
informationistransmittedfromthereticularformationtothethalamus,andfromthereto
thecerebralcortex,wherethesensationofpainisfinallyperceived[19].Theprocesses
involvedinpainperceptionincludetransduction,transmission,modulation,projection,
andperception.Transductioncorrespondstothetransformationoftheharmfulstimulus
(inthiscase,mechanical)intoanelectricalimpulse[64]generatedbynociceptorsinthe
skin,muscles,bones,orviscera[65].Whenactivated,thesenociceptorsgeneratetheaper‐
tureofCa2+,K+,orNa+ionicchannelstocreatetheelectricalimpulsesthattravelthrough
neuronalaxonstocarrythenociceptivesignal,successively,tothespinalcord,brainstem,
thalamus,andcerebralcortex[66].Inthisprocess,informationistransmittedthroughAδ
nerveterminalsthatcanbenociceptiveornonnociceptiveandarecomposedoflow‐
threshold(<75%)andhigh‐threshold(>25%)mechanoreceptorsandmechanothermalre‐
ceptors.ThelatterarereferredtoasAδheatnociceptors.High‐thresholdAδnociceptors
respondonlytotissue‐threateningortissue‐damagingstimulation.ManyoftheAδnoci‐
ceptorsrespondonlytospecificstimuli,whereasothersarepolymodalandrespondto
mechanical,chemical,andthermalstimulation[67].Inaddition,accordingtoBasbaumet
al.[68],firstandsecondpainreferstotheimmediateanddelayedpainresponsestonox‐
iousstimulation.Othertermsthatdenotethesepainsarefastandslowpainor
sharp/prickinganddull/burningpain.Thestimulithatgeneratefirstpainaretransmitted
byA‐delta,small,andmyelinatedafferents.SecondpainresultsfromtheactivationofC

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fibres,whichconductimpulsesmuchmoreslowly,thusaccountingforthetimediffer‐
ence.Reactiontimestofirstandsecondpainareabout400–500and1000ms,respectively.
Lesionstriggerthereleaseoftheproinflammatorycytokines(prostaglandins,leukotri‐
enes,bradykinin,serotonin,histamine,substanceP)thatconstitutetheso‐called“inflam‐
matorysoup”[69].This“soup”cancause,orintensify,nociceptiveimpulsesthatfacilitate
paintransmission[65].Transmissionisfollowedbymodulation,whichbeginswhenthe
stimulusiscarriedtothedorsalhornofthespinalcordinRexedlaminaeI,II,andV[70].
Theseeventsstimulatevariousbrainregions,includingthecerebralcortexandreticular
formation,whichtransmitsensoryinformationfromthethalamus.Thisisthepointat
whichtheperceptionofpaininthethalamusandcerebralcortexoccursthroughthespi‐
nothalamicandspinoreticulartracts[19,71](Figure1).

Figure1.IllustrationoftheroutefollowedbythenociceptivetransmissionfromtheperipheralnervestotheCNSafterthe
initialreceptionoftheharmfulstimulusduringabullfight(i.e.,placingofthebanderillas).Theprocessincludestransfor‐
mationoftheharmfulstimulusintoanelectricalimpulsegeneratedbynociceptorsintheskinandmusclesthatgenerate
theapertureofCa2+,K+,orNa+ionicchannelstocreatetheelectricalimpulsesthattravelthroughneuronalaxonstocarry
thenociceptivesignaltothespinalcord.Inthisprocess,informationistransmittedthroughtwoprimaryafferentnocicep‐
tiveneuronscalledAδandCfibrestothedorsalhornofthespinalcordandisthenprojectedbyelectricalimpulsesand
brainstemtothethalamus,reticularformation,andcerebralcortex,wherethepainisperceived.
2.2.EmotionsandPain
Somestudiesofbeefanddairycattlehaveusedtheextensionofeyewhiteandear
positionasindicatorswhenevaluatingtheemotionalstatesofanimals.Battinietal.[72],
forexample,analyzed430photographsoftheheadsofdairycowsclassifiedinfourlevels
accordingtothedegreeofeyeopeningandearposition.Forthelatterindicator,drooping
earsindicatedgreaterrelaxation,whileanuprightearpositionsuggestedgreaterexcita‐
tion.Thismodelwastestedunderdifferentconditions:duringfeeding,whileatrest,and
whilegrazing,complementedbyanavoidancedistancetrialatthefeedingplace(ADF).
Theirfindingsshowedthatwhentheanimalswererelaxed,theireyestendedtoremain
half‐closedandtheirearsdrooped(67.8%ofhalf‐closedeyes,77.3%withearsdrooping
orbackward,whilegrazing).Inthecaseofexcitation,incontrast,thewhitesurfaceofthe
eyeincreasedinextensionandwasmorevisible(excitementduringtheADFtestshowed
44.8%ofeyewhiteclearlyvisible),andtheearswerepushedforwardtowardstheap‐
proachingevaluator(95.5%).Thoseresultssupportusingeyewhiteandearpostureas

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reliableindicatorsofemotionsindairycows.Theeyewhiteindicatorwasalsotestedby
Coreetal.[73]topredicttemperamentinaherdofcattle.The147animalsstudiedwerea
mixofBritish(predominantlyAngus),Continental(predominantlySimmental),andPied‐
montesebreeds.Theyweregroupedasheifers(n=48),bulls(n=39),andsteers(n=60),
andthenvideotapedwhileinasqueezechutewheretheywereselected.Chutetempera‐
mentscoreswereassignedasfollows:1(calm)to5(agitated),andtheeyewhiteareawas
expressedasthepercentageofexposedeyearea.Thoseauthorsfoundthehighestaverage
percentageofeyewhiteinthebulls(31.43±14.77),followedbytheheifersandsteers
(30.14±14.37and28.57±12.38,respectively).ThePearsoncorrelationcoefficientsforeye
whitepercentageandchutetemperamentscoreswere0.95forbulls(p<0.0001),0.674for
heifers(p<0.0001),and0.696forsteers(p<0.0001).Thus,theyconcludedthatthepercent‐
ageofeyewhiteincattlecanbeusedasaquantitativetoolthatrequiresminimalequip‐
menttoassesstemperamentinbeefcattle,andthatitprovidesanobjectivemethodfor
temperamentselection.Theseindicatorsmight,therefore,alsobeusedasnon‐invasive
toolsforevaluatingthedegreeofexcitationinfightingbulls,thoughunderdifferentcon‐
ditions.
Fightingbullsarerearedinextensiveenvironmentswithminimalexposuretohu‐
mans.Fearisarguablythemostinvestigatedemotionindomesticanimals.Itisapotent
stressor.Thehighlyvariableresultsarelikelyduetodifferentlevelsofphysiologicalstress
suchasfearstress,includinghandling,contactwithpeople,orexposuretonovelty.How‐
ever,welackscientificstudiesofthisbreedthatevaluatethedegreeofexpressionofpos‐
itiveandnegativeemotionsunderdifferentconditions.Sincethestimulithatcancause
fearinbulls—andotheranimals—duringfightsincludeconfrontingaclosed,unfamiliar
environment,isolation,separationfromconspecifics,exposuretopredatorsoraggressors,
theabsenceofescaperoutesorrefuge,andthepresenceofharmfulstimuliinconditions
thatprecludeescape[74].Painandemotionarepartofamoreextensivemotivational
systemthatpromotessurvival,andtheneurocircuitriesassociatedwithemotionandpain
overlapsignificantly[75].
2.3.AnalgesicEffects
Itispossible,however,thatthestressprovokedcouldinhibitthetransmissionofpain
stimuliinthebrainandspinalcord[76].Tobecomeeffective,thispainreductionprocess
mustbeactivatedbytheamygdala.Thisinvolvesendogenousopioidsthatmodulatesig‐
nallingandsynaptictransmissionintheneurallocithatcontributetotheexperienceof
pain[77].Thegeneticmakeupandaggressivebehaviourtypicaloffightingbullsduring
eventsleadsthemtoadoptachallengingattitudeastheyconfronttheirattacker,making
noattempttofleefromthesituation.Theactivationofneuroendocrinemechanismsallows
releaseofthehormoneproopiomelanocortin(POMC),β‐endorphins,andmethaneceph‐
alins,cortisol,andACTHinresponsetostress.Centenera[78]tookbloodsamplesfrom
fightingbullsatfourstagesoftheevent:immediatelyuponenteringthering(n=159
bulls),afterthewoundsinflictedbythelance(n=137bulls),aftertheplacingoftheban‐
derillas(n=110bulls),andattheendofthefightwhenthebulliskilled(estoque)(n=80
bulls).Theirpost‐eventfindingsshowedanincreaseintheconcentrationofPOMC—a
precursorhormoneoftheβ‐endorphinsandmethanecephalins—thatwassixtimes
higherintheanimalsaftertheestoquecomparedtotheconcentrationsdeterminedwhen
thebullsenteredthering(p<0.01).WithrespecttoserumACTHandcortisollevels,that
studyfoundhigherconcentrationsinthebullsimmediatelyafterleavingthering,while
thelowestvaluesweredeterminedforthesamplesdrawnandanalyzedafterthefinal
estocada(fourandthreetimeslower,respectively)(p<0.01).
3.Muscle‐SkeletalInjuriesduringBullfights
AccordingtoFernándezandVillalón’s[11]anatomicalreview,fightingbullslack
clavicles,sotheirtwoanteriorextremitiesarejoinedatthetrunk,mainlybymuscles.The

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scapulahasaprolongationcartilagewherethosemusclesareinsertedtojointhetwoex‐
tremitiesmorestronglyandfixthemtothetrunk.Musclefibres,ofcourse,areclassified
histologicallyinvarioustypesaccordingtotherelationbetweenmyosinadenosinetri‐
phosphataseactivity(m‐ATPase)andpH[79].WhenpHisalkaline,typeImusclefibres
(slow‐contracting)havelowm‐ATPaseactivity,whiletypeIIfibres(fast‐contracting)have
highm‐ATPaseactivity[80].Underconditionsofintenseexercise,suchasabullfight,the
fast‐contractingmusclefibreswithlowoxidativecapacity(typeII)arethemainonesthat
functiontoproduceanaerobicglycolysisasapathwayforproducingtheenergyrequired
fortheeffortinvolved.Duringthisprocess,eitherpyruvateisformedandusedbythe
mitochondria,orlactateisproduced,whichis(partly)deliveredtothebloodstream.From
there,itreachestheliverandkidneysthatconvertittoglycogen,asoccursinothermam‐
malspecies,includinghumans[81–84].Theenzymelactatedehydrogenasecatalysesthe
interconversionofpyruvateandlactate.However,whenlactateisabundant,itremains
detectableandindicatesrecentlyperformedheavyphysicalactivity.Increasedphysical
activitymayalsoinducedamagetomusclefibresandthereleaseofcreatinephosphoki‐
nase(anenzymeusedbythemusculartissueforproducecreatine)intotheblood[85].
Duringbullfights,bullsaresubjectedtoanatomicalinjuriessuchastornmuscles,liga‐
ments,tendons,andrupturednervesandbloodvesselscausedbythebullfighters’weap‐
ons[11].Otherinjuriesthatmayoccurincludefracturesoftheribs,thespinousprocesses
onthevertebrae,andprolongationcartilages[11]thatcouldcauseseverepainand
changesintheanimal’sneurobiology.
Gomarizetal.[12]attemptedtodeterminethecausesofthephysiologicaldisequilib‐
riumofthelocomotorapparatusbyevaluatingvarioustransversalcutsofseveralmus‐
cles—commondigitalextensor,longdigitalextensor,longthorax,Latissimusdorsi,Ven‐
tralthoracicserrate,andgluteobiceps—fromsixfightingbullskilledbythematador’s
swordthatpresentedanobviouslackofstrengthbeforedeath,manifestedinfrequent
fallsrecordedintheirmovementprofile,asTable1shows.Theyusedhistologicaland
histochemicaltechniques,stainedtheirsamplesandthenmicrophotographedthemat10×,
20×,and40×.Findingsallowedthemtoidentifythefollowinglesions:mitochondrialal‐
terations,lossofthepolygonalcontouroffibres,centralizationofnuclei,necroticpro‐
cesses,fibrillarfragmentation,andvacuolizationofthesarcoplasm.Insomesubjects,the
injuriesexaminedwereaccompaniedbyalterationsoftheconnectivetissue(perianden‐
domysialfibrosis).Theauthorsconcludedthatthisseriesofinjuriescouldbeaconse‐
quenceoftheexcessivemusculareffortthatthebullsmadeinashorttime‐period.They
didnotruleoutthepossibilitythatsomeoftheanimalsmayhavesufferfromamyopathy.
Whateverthecase,theysuggestthatthelesionsaffectedmusclefibresandconnectivetis‐
sue,leadingtoalossofstrengthandfrequentfallsduringthebullfights.
Table1.Contributionofmusclestomovementinfightingbulls.
MuscleGroupFunction
Commondigitalextensor,gluteo‐
b
iceps,andlongdigitalextensor Supportinextendingandretractingextremities
Longthorax
Fixingandrightingactionoftherachis;dorsalflexor
agentofthethoracic‐lumbarrachis;regulatingme‐
chanicalinfluencesintheprotraction–retractionof
pelvicmembers
Latissimusdorsi
Whencontracted,oncetheprotractionofthethoracic
memberisculminated(supportinextension);drags
b
odymasswhileretractionofthememberlasts
VentralthoracicserrateConstitutestheprincipalsuspensoragentofthe
trunk.
FromGomarizetal.[12]

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Inadditiontotheinjuriesvisibleatfirstsightduringabullfight,thereareconditions
infightingbullsthatcouldexacerbatemuscularandskeletaldamage.Thestudyof120
fightingbullsbyLomillos‐PérezandAlonsodelaVarga[86]detectedthepresenceofos‐
teochondrosisinover70%oftheanimalsevaluated,bilaterallyin78.3%ofthem.Various
authorsidentifyosteochondrosisasanelementthatpredisposesfightingbullstodevelop
theso‐called“fallingsyndrome”[87,88],anafflictioncharacterizedbylossofequilibrium
andtransitoryfallingthathasalsobeenassociatedwithdamagetomusclecells[12].
Martínez[89]andLomillos‐Pérezetal.[90]reportedthatcausesofthefallingsyn‐
dromecanincludegeneticfactors,transportconditions,thephysicaldemandsofthebull‐
fight,alackoffunctionalexercise,alimentarydeficiencies,andcirculatory,nervous,met‐
abolic,endocrine,oretiologicaldisorders.AccordingtoLomillos‐Pérezetal.[90],thissyn‐
dromehasdecreasedovertime,asincidencehasdecreasedfrom99.56to79.82%,andthat
itisinthethird(cape)stageofthebullfightthatitoccursmostfrequently.Eventhough
theincidenceremainsveryhigh,itisnoteworthythatthispartialdecreaseinincidence
occursduringthebanderillasstage.Dávilaetal.[91]pointoutthatanydiscussionofthe
aetiologyofosteochondrosisinfightingbullsmustmentionthetraumaandbiochemical
elementsofthecartilage,whichcanbeaffectedbynutritionaldeficiencies,hormonalim‐
balances,inadequatevascularcontribution,andgeneticfactors.
4.HypovolemicShock
Thewoundinflictedbythelancecausesalossofbloodvolume,thefirsteventina
seriesthatendsinhypovolemicshock[10].Hypovolemiaisthereductionofbloodvolume
duetomassivehaemorrhagingthatinducesseveredehydration.Inthiscondition,both
theamountofbloodthatreachesthebody’svitalorgansandthepressurewithwhichit
arrivesareinsufficient,impedingtheirfunctioningandviability[92].Threephasesof
hypovolemicshockhavebeendescribed:compensatory,inwhichtheorganismgenerates
aneuroendocrineresponseasitstrugglestomaintainhaemodynamicstatus;decompen‐
satory,whenitsustainscontinuoushypoperfusionthattriggersaprocessofcellinjury
anddeath;andmicrocirculatorydysfunction,whentheparenchymaltissueisdamaged
andinflammatorycellsareactivated[93].Thisconditionispartiallycompensatedatonset
bythereleaseofK+ionsfromtheintracellularspacetotheblood.Thismechanismaimsto
self‐compensateandcauseisotonicdehydrationandhyperkalaemia,buttheresultinghy‐
droelectrolyticimbalanceproducesvasculardysfunction.Atthesametime,othercom‐
pensatingmechanismsareactivatedtolowerarterialpressure.Thisisdetectedinitially
bybaroreceptorsintheaorticarchandcarotidsinus,leadingtoactivationofthesympa‐
theticsystemthatsecretescatecholamines,angiotensinII,andtheantidiuretichormoneto
preservecardiacoutputandmaintainadequatecerebralandcardiacperfusion[94].
Otheressentialresponsesofthefightingbull’sorganismduringabullfightinclude
spleniccontraction,whenerythrocytesaremobilizedtowardsthezoneswhereadditional
oxygensupportisrequiredwithincreasedhaematocritduetothedehydrationtheani‐
malsmaypresentasaconsequenceoftheintensephysicalactivityperformedinashort
period[51].
5.MetabolicResponsesLinkedtoPsychologicalStressandPhysicalExercise
Animalsaresubjecttovariousenvironmentalandbehaviouralstressorsthataffect
theirsurvivalandphysicalstate[95].Torespondphysiologicallytothesestressors,they
presentaseriesofneuralandendocrineresponsesthatdivertenergyawayfromshort
term,non‐essentialphysiologicalprocessessuchasgrowth,digestion,andreproduction,
inanefforttoresolvethestressfulsituation.Meanwhile,theneuralstressresponsein‐
volvessecretingcatecholaminesfromtheadrenalmedullaandthesympatheticnervous
system,andmobilisingenergytoincreasecardiacfrequency,bloodpressure,andrespira‐
tion[96,97].
Theexertiondemandedofbullsduringthe15–18minthatbullfightsusuallylastcan
beconsideredsimilartothatperformedbyathleticanimalsforcedtoperformenormously

Animals2021,11,282010of16

intensiveexercise[52,98].Thisexplainswhyacid–basebalancealterationsareobserved
thatlowerbloodpH[51].Undertheseconditions,bloodpHcandecreasetolevelsbelow
7.2,aerobicglycolysisisinhibited,extracellularosmolarityincreases,andcellularoedema
mayoccur.Itiswellknownthatincreasedaciditycanproduceabroadrangeofharmful
effectsonneuralfunctioning,suchasincreasingthepermeabilityoftheblood–brainbar‐
rier,inhibitingmitochondrialfunction,andalteringsynaptictransmissionandionicfunc‐
tions[99].Amongthemechanismsthattheorganismhasatitsdisposaltoeliminatehy‐
drogenionsandmaintainpH,wecanmentionseveralbufferingsystems,suchastheres‐
piratoryandbufferbases[100].
Bullfightsdemandanenormousphysicaleffortbythebulls,sotheseanimalsmustbe
inoptimalhealthconditionsbeforeparticipating.Theintensityofthefighttriggerssignif‐
icantmetabolicalterationsthatareobservableaftertheevent,includinghaematological
changes(increasedredbloodcellsandhaematocrit),andelevatedperoxidesandlacticacid
productionthatreduceconcentrationsofmuscleglycogenandpH[101].Accordingly,
LacourtandTarrant[102]andAgüeraetal.[103]showedthatthephysicalandemotional
stressandexercisetowhichfightingbullsaresubjectedduringaneventcausesamarked
reductionofglycogenintypeIandtypeIIfibres.Thesechangesareaccompaniedbythe
releaseoflargeamountsofenzymesintothebloodstream,includingcreatininekinase
(CK),lactatedehydrogenase(LDH),andaspartateaminotransferase(AST)[52].Theante‐
mortemanalysisofcertainbiologicalvariablesinanimalscanbeusefulfordiagnosing
diseasesordetectingmetabolicstates[104].Fightingbullsareknownfortheiraggressive‐
nessandnaturalresistancetohandling,sodrawinginvivobloodsamplescanbeex‐
tremelydifficult[105].Althoughtheemotionalandphysicalstressthatthesebullsexperi‐
enceduringbullfightscancausesignificantchangesinbloodanalytelevels(Figure2),
bloodvariablesareinfluencedbyphysicalexertionandstressfulsituations;consequently,
post‐mortembloodanalysisdoesnotreflectbasalconcentrationsforthisspecies.There‐
fore,theseindicatorscannotalwaysbeusedasdiagnosticfindingsinpost‐mortemblood
evaluations[106].However,ocularfluidssuchasvitreoushumourmaintainastablecom‐
positionafterdeathandcanbeusedpost‐mortemtoestimatethebloodlevelsthatanimals
presentedantemortem.González‐Montañaetal.[105]usedpost‐mortemocularfluidsin
fightingbulls,findingthatallthevariablesassessedinplasmashowedconcentrations
abovebasallevels.Specifically,alterationswereobservedforglucose,uricacid,LDH,and
creatininekinase(CK).Thesefindingscanbecausedbytheoverexertion,stressfulsitua‐
tion,destructionofmusclecells,andlossofbodilyfluidsthatthebullsundergoduringthe
intenseexerciseofabullfight.Severalstudiesofpigsandhorsesshowedthatanimalsper‐
forminghighlevelsofphysicalactivityandtraininghaveacorrespondinghigheroxidative
capacity,higherglycogencontent,andlargeramountsoftypeIImusclefibresthananimals
thatperformlessphysicalactivity[106–109].Itseemsthatthemetaboliccapacityofbulls
variesaccordingtoage.AstudyofyoungandmaturefightingbullsbyAgüeraetal.[103]
analysedthevaluesofcitratesynthase(CS),3‐hydroxyacylcoenzymeAdehydrogenase
(HAD),LDH,glycogen,lactate,andpHinbiopsiesofthegluteusmediusmuscleobtained
afterbullfights.TheyobservedthatHADandLDHactivitywerehigherinthegroupof
olderbulls.GlycogenconcentrationsandpHwerelowinbothgroups,butlactateconcen‐
trationswerehigherintheolderbulls.Theseresultsshowthatyoungandoldbullshave
similarmusclefibretypecompositionbutthemetaboliccapacitydiffers,withahighergly‐
colyticcapacityandlactateproductioninolderbulls[103].Inanotherstudy,Purroyand
Buitrago[110]observedthatthelevelsofCK,oxalacetateglutamatetransaminase(GOT),
andLDHwerehigherpost‐mortembecausetheanimalshadbeensubjectedtomorein‐
tenseexerciseinthedaysleadinguptobullfights.Whenthedataobtainedafterexercise
infightingbullswerecomparedtonormalreferencevaluesforcattle,itwasclearthatsome
bloodvariables—pH,bicarbonate(HCO3−),baseexcess(BE),oxygenpartialpressure(PO2),
andoxygensaturation(sO2)—decreased,whileothers—sodium(Na+),potassium(K+),cal‐
ciumion(iCa),andhaematocrit(Htc)—remainedwithinnormallimits[51].Otherana‐
lytes,suchasPCO2,haemoglobin(Hb),andlactate,wereabovenormalvalues.Astudyby

Animals2021,11,282011of16
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Muñoz‐Juzadoetal.[111]evaluatedtheoxidativeandglycolyticpotentialinmusclebiop‐
siesoffightingbullstakenafteranevent.Samplesweredrawnfromthegluteusmediusand
semitendinosusmusclesofbullsaged1to3years.Thoseauthorsfoundthatthehighest
oxidativemuscularpotentialwasmanifestedinthe2‐year‐oldbullsandthatglycolytic
capacityincreasedprogressivelywithage.Thiscontrastswithotherbovines,whereare‐
ductionintheoxidativepotentialoccursfromthetimeofbirthonwards[102].Thesefind‐
ingsleadtothesuggestionthattheageofthebullmightparticipatesignificantlyinthe
metabolicresponsesduringbullfights,asitdoesinmuscleenzymeproduction.Physiolog‐
icalresponsesarethereactionstostressfulstimulithatoccurinorganisms.Heartrateis
themostusefulparameterforevaluatingtheactivationoftheflight‐or‐fightsyndrome
[103].Whencorrelatedwithbodytemperature,itcanbeinterpretedastheheart’sresponse
tometabolicdemand[92].Likewise,skintemperatureisausefulparameterforevaluating
vascularresistance,vasodilatation,andvasoconstriction.Whenbodytemperaturede‐
creasesdistally,vasoconstrictionispresentwithlowcardiacoutputandlikely,hypovole‐
mia[112].If,incontrast,thetemperaturetendstoincreasetowardsdistalareas,vasodila‐
tationisoccurringwithhighcardiacoutput[113].Finally,tocompensatetheconditionof
metabolicacidosis,animalspresenthyperventilationortachypnea,whichcanbedetected
bytheflaringorflappingoftheirnostrilsandmoreevidentinspiratorymovementsofthe
abdominalandthoracicwalls.

Figure2.Metabolic,haematological,andacid–basebalancealterationsthatoccurduringtheendo‐
crineresponsetostressandthephysicaleffortinfightingbulls.Oneofthemainmetabolicresponses
thatoccursduringstressfulconditionsconsistsinanincreaseofadrenalglucocorticoids,suchas
cortisol,thatcirculateinthebloodstream[95].Inotherspecies,itiswellknownthatshortperiods
ofglucocorticoidreleasecancauseirreversibledamage,includingreproductivedisorders,immu‐
nosuppression,andreducedlifeexpectancy[96,114,115].Inaddition,theemotionalstressandin‐
tenseexercisethatfightingbullsundergoandtheexposuretoanewenvironmentduringtheevent
producemarkedincreasesofcortisol,glucose,andT3inthebloodstreamthatcangeneratesignifi‐
cantbiochemicalchangesintheorganismbytriggeringthestress‐adaptationsyndrome[52].Cate‐
cholaminesfunctiontoprepareanorganismforthe“flight‐or‐fight”responsebuttriggerstachycar‐
dia,hypertension,hyperthermia,hyperventilation,andsweating[48,116].Cortisolbeginstobese‐
cretedbytheadrenalcortexaroundfiveminutesafterthestressfulstimulusispresented.Thissub‐
stance,whichcanbedetectedinblood,saliva,urine,andfaeces,performstheprimaryfunctionof
increasingandthenmaintainingbloodglucoselevelsusingreservesofhepaticandmusculargly‐
cogentoprovidetheanimalwithsufficientenergytosustainthephysicaleffortthatthesituation
demands[117].CRF:corticotropinreleasingfactor;HPA:hypothalamic‐pituitary‐adrenocortical
axis;ACTH:adrenocorticotropichormone;ATP:adenosinetriphosphate;ANS:autonomicnervous
system;HR:heartrate;RR:respiratoryrate;CK:creatinekinase;LDH:lactatedehydrogenase;AST:
aspartateaminotransferase;ROS:reactiveoxygenspecies;BBB:blood–brainbarrier.

Animals2021,11,282012of16
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AccordingtoGarcía‐Belengueretal.[118],fightingbullspresentlowseleniumand
vitaminElevelsbuthighcopperlevelsintheblood,possiblyassociatedwithexercise
duringthefight.Carpinteroetal.[119]identifiedthatcalcium,phosphorus,andmagne‐
siumlevelsarewellabovenormalphysiologicalvaluesafterbullfights.Theyattributed
hypercalcaemiaandhypermagnesaemiatodehydrationduringfightsandthefindingof
hyperphosphatemiatorespiratoryandlacticacidosis.Afterabullfight,highmagnesium
andphosphoruslevelswerereportedbyGonzález‐Montañaetal.[120]in15fightingbulls
aged4–5years,basedonmeasurementsofthevitreoushumour,aqueoushumour,and
blood.Theyalsodeterminedthattheselevelswerehigherinbloodplasmathaninthe
vitreoushumour,whilecalcium,chrome,andsodiumlevelsweresimilarinallthreeflu‐
ids.Selenium,iron,zinc,andcoppervalueswere16–32timeshigherinplasmathaninthe
ocularfluids.Insummary,studieshavefoundthatchangesatthemuscularlevelandin
diversebodyfluidsresultfromthephysiologicaleffortandenergydemandtowhich
fightingbullsaresubjectedduringbullfightingevents[103,111].Themostsignificant
changesfromtheperspectiveofanimalwelfareincludethoserelatedwithpsychological
stress[121]withnegativeemotions,includingfear,pain,andtriggeringphysiologicalre‐
sponses,includingdehydration,hypermagnesaemia,hypotension,muscularnecrosis,
myoglobinuria,andmetabolicacidosis.
6.Conclusions
Theexistinginformationallowsustoconcludethatbullsfaceenergyandmetabolic
demandsduringbullfightsduetothehighintensityanddurationoftheexerciseper‐
formed,togetherwithmuscularinjuries,physiologicalchanges,andhighenzymeconcen‐
trations.Inaddition,thefinalstageofthebullfightcausesaslowdyingprocessforan
animalthatissentientandconsciousofitssurroundings.Unfortunately,duetothescant
literatureonthisbreed,manygapsexistintheavailableinformation;morespecificinfor‐
mation,suchasphysiologicalevaluations,couldhelpverifytheseeffects.
AuthorContributions:Conceptualization,D.M.‐R.,A.O.,andA.V.;methodology,D.M.‐R.,A.S.,
J.M.‐B.;investigation,D.M.‐R.,A.O.,I.H.‐Á.,P.M.‐M.,J.M.‐B.,F.N.,andA.V.;writing—originaldraft
preparation,D.M.‐R.,A.O.,F.N.,I.H.‐Á.,P.M.‐M.andA.S.;writing—reviewandediting,A.O.D.M.‐
R.,I.H.‐Á.,P.M.‐M.andJ.M.‐B.;finalsupervision,A.O.,andD.M.‐R.Allauthorshavereadand
agreedtothepublishedversionofthemanuscript.
Funding:Thisresearchreceivednoexternalfunding.
InstitutionalReviewBoardStatement:Notapplicable.
InformedConsentStatement:Notapplicable.
DataAvailabilityStatement:Notapplicable.
ConflictsofInterest:Theauthorsdeclarenoconflictofinterest.
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