ELSEVIER Applied Animal Behaviour Science 55 (1997) 153-162

APPLIED ANIMALBEHAVIOUR

SCIENce

Intercat aggression: a retrospective study examiningtypes of aggression, sexes of fighting pairs, and

effectiveness of treatment

Ellen M. Lindell a,· , Hollis N. Erb b, Katherine A. Houpt C• 6 BrennerRidgeRd, Pleasant Valley. NY J2569. USA

b Department of Epidemiology. New YorkStateCollege of Veterinary Medicine. CornellUniversity.Ithaca, NY 14853. USA

C Department of Physiology / AnimalBehaviorClinic, New YorkStale Collegeof Veterinary Medicine.Comell Unioersit», Ithaca, NY 14853.USA

Accepted 14 January 1997

Abstract

Aggressionamong cats in the same household is a common behavioral problem.To determinehow best to resolve this problem, 48 cases of intercat aggression were examined retrospectively.Clients were contacted by telephone so that the outcome of the treatment program could bedetermined. Thirty cases were considered cured, and 18 were not cured. Male cats initiatedaggression in more cases than did female cats; the aggression was equally likely to be directedtoward a same sex or opposite sex victim. There was no significant difference in the number ofcures for anyone pair of sexes. No one treatment modality resulted in a significantly greaternumber of cures than any other treatment.The use of buspirone was associated with a significantdecrease in likelihood of cure. We concluded that treatment protocols for cases of intercataggression must be tailored to the individual cats involved. Clients seeking to adopt a second catmay be advised that successful integration may be related to features, in particular the gender, ofan individual cat. © 1997 Elsevier Science B.Y.

Keywords: Cat; Aggression; Agonistic behavior; Social behavior

• Corresponding author.

0168-1591/97/517.00 ~ 1997 Elscwier Science B.V. All rights reserved.PJI 50168-1591(97)00032-4

154£.M. Li"ci~1I et "I. / App/j('tl Animal B~lult;iuur SCI~nc~ 55 I/CJ97J /53 -/6~

1~5

I. Introduction

.Cats are popular house pets, generally demanding lillie while providing companion-ship to busy owners. But the cat that may be content to live in proximity to humans. andeven do~s. may not tolerate feline housemates in close quarters.

Cats anconfine~ areas with ~1 abundant food supply form matrilineal groups. Youngmales usually emigrate. A SOCial group of feral cats. in which adults are generallytolerant of o.ne another. might include an overlap of home ranges (Kerby and Macdon-ald. 198~~ Liberg and Sandell. 1988). However. an individual cat generally maintains itsown actively defended te~tory within this home range (Beaver. 1992). Threat displaysmay p~e~enl ?ven aggressron. Furthermore, a social group will not permit another adultcat to Joan (Liberg and Sandell, 1988).

A house cat may not have an opportunity to establish an adequate territory. Whereasferal cats ma~ have mean home ranges from 0.51ha to 620 ha (Beaver. 1992). walls and~oors determine the available utilizable space for house cats. Within these artificiallylm~sed qu~ers. house cats are reponed to engage in 'time-sharing'. a phenomenon inwhich favorite areas are occupied in a temporal sequence (Bernstein and Strack, 1993).A second method of sharing involves ·physical' sharing of an area (Bernstein andStra~k, 1993). A cat must tolerate the close contact of other cats in order to live in amulti-cat household without displaying aggression.

Th~ p.urpose of this retrospe~tive study was to determine whether cats of anycombination of sexes were more likely to be presented to a behavior consultant for thetreatme?t of interc~t aggression. In addition, this study examined whether the probabilityof a satisfactory ch~lcal outcome was affected either by the gender of the cats involvedor by the use of vanous treatment modalities.

2. Material and methods

The cases reviewed were presented to the Animal Behavior Clinic at New York State~ollege of VeterinaryMedicine at Cornell University between 1988 and 1994. Consulta-uons were c~nduct~d thr~ugh telephone interviews, typically I h long, and weresupplemented If possible with video recordings of interactions between the cats. At theend of.a consu~t~u.on,. each .owner was provided with a diagnostic and therapeutic plan.Followl.ng the 1Il.ltlal Interview. clients received letters summarizing the verbal recom-mendations, Copies of.the letters as well as recommendauons regarding drug treatmentswere sent to the refernng veterinarians.

Follo~-up postcards were routinely sent to clients 1-6 months after the initialconsultauon so that the progress of patients could beupdated. The postcards which werereturned as well as any othe~ correspondence remain in the case history tile.

For the nreeenr c:t1vl\J ,.J~~C'_~up~ •..-...n:", 1),;li.dm lII'un~ case Dlslory tHe..~or the prese~t study, clients were contacted by telephone. The interval from the

ora.glnal consuhation to the .(oHow-upcommunication ranged from 6 months to 6 years.Clienrs w~re asked to descnbe the ?verall outcome of the treatment program as one ofthe following: cured-no further evidence of aggression; able to tolerate-some aggres-

sion continued to be observed but intensity was low and considered acceptable by theowners; permanent separation-cats could no longer live in a shared space; given away-one or both cats were rehomed: euthanized-s-either the victim or the aggressor. Thefirst two groups were considered to have a satisfactory outcome and were categorized asthe 'cure' group. The last three outcomes became the 'no cure' group. The authorsrecognize that this method for rating the outcome relies on clients' perception of theoutcome rather than the measurement of specific behaviors. In clinical situations, it isthe client's perception that determines the disposition of the pet.

Clients were also asked which treatment suggestions they had implemented, andwhether they felt that any particular treatment had contributed to the success or failure toresolve the problem. The original treatment suggestions consisted of one or more of thefollowing: separation, positive reinforcement for reintroduction, cat carrier, odor ex-change, collar-bell, and pharmacological intervention. Separation involved physicallyseparating the cats except for meal times. Positive reinforcement for reintroduction ofseparated cats involved the use of positive reinforcement in the form of preferred food.A non-aggressive cat earned the food reward. With each successful session, that is, ifthere had been no aggressive behavior during the last meal, the food dish of each catwas moved closer to the other. Use of a cat carrier involved the restraint of one or bothcats in separate cages or cat carriers during meals, which was the only time the cats weretogether. The intent of the use of restraint was to interrupt the chase-flee cycle. Odorexchange entailed asking owners to rub each cat with the same towel, attendingspecifically to the glandular areas of the cheek and tail. Using a collar-bell involvedattaching a bell to the collar of the aggressor cat, to prevent that cat from startling thevictim cat by warning the victim cat of his approach. In this study. the cat whichinitiated the oven fighting and pursuit was considered to be the aggressor. The cat thatwas chased or that avoided or ned from the aggressor was considered to be the victimcat.

Pharmacological intervention included the use of psychotropic drugs as have beendescribed in Marder's review (Marder. 1990. Before administering medication. allclients and referring veterinarians were advised to assess the general health status of thecats through serum chemistry profiles, Victim cats received diazepam. a benzodiazepinethat has been used successfullv 10 treat fear-induced behavior problems (Marder, 1991).Aggressor cats received one 'of three medications. Amitriptyline, a tri-cyclic anti-de-pressant. has been reponed to decrease aggressive behavior (Houpt and Reisner, 1995).Buspirone, a serotonin agonist with minimal risk of side effects. has been usedsuccessfully to treat canine and feline aggression (Dodman and Shuster, 1994). Mege-strol acetate (Ovaban, Schering-Plough Animal Health, Kenilworth, NJ) has been usedsuccessfully to treat aggression in dogs and cats, but its long-term use carries thepossibility of serious side effects (Marder, 1991).

Table I contains a list of all cats included in this study with reference to the outcomeof the case. the zender and aze of a22reSSOr and victim cats. which cat was the firstof the case, the gender and age of aggressor and victim cats, which cat was the firstresident of the household, and which cats received medication. A total of 18 compar-isons were tested to determine an effect on the probability of a cure. These statistics arepresented in Table 2. Two by two contingency tables were tested with Fisher's exacttest. Larger tables were tested by use of X 2 test. When the X 2 test had an expected cell

156 £.M. Lindell et ClI./Applied Animal Behaoiour Science 55 (/997) /53-/62 E.M. Lindell et al. / Applied Animal Behaviour Science 55 (1997) 153-162 157

Table I Table 2Age (in years) and sex of aggressor (Agg) and victim (V) cats presented for intercat aggression Comparisons of combinations of gender and treatment modalities and the probability of cure (P)

Case Aggressor Victim First resident" Outcome Comparison Cure No cure

Age Sex Med- Age Sex Med Aggressor: male/female 18/12 12/5

5 M Bu F None Agg CureVictim: male/female 14/13 6/11

7 F None M 0 ? CureSex pair: mm/ff/mf or fm 10/7/10 5/3/8

3 I M None F 0 Victim CureNo. of treatments tried: 1/2/3 or 4 10/7/12 5/5/8

4 J M None J M 0 Both CureMedicationused: yes/no 22/8 13/5

5 12 M Nune 10 F 0 Victim CureSeparation used: yes/no 21/9 16/2

6 10 F None 16 F None ? Cure+ reinforcementused: yes/no 11/19 6/12

7 M Bu M None Victim CureOdor exchange used: yes/no 10/20 5/13

8 5 M None M None Victim CureMedicationonly treatment used: yes/no 7/23 2/16

9 5 M Am M 0 Agg CureAggressor received meds: yes/no 13/17 8/10

10 16 M None M None Agg CureVictim received meds: yes/no IS/IS 9/9

II 5 F Am/Bu M 0 Agg CureAggressor and victim meds: yes/no 6/24 4/14

12 5 F Ovaban F 0 '! CureMeds: A+V/ A only/V only/neither 6/1/9/8 4/4/5/5

13 I F Am M 0 CureMeds aggressor only/victim only 7/9 4/5

14 3 F None F None Agg CureMeds, separation and: no other tx/ + rft/odor exch/ +rft and odor exch 3/5/3/4 5/2/2/2

15 9 F None 10 M None ? CureBuspirone to aggressor: yes/no 5/25 8/10 p < 0.05

16 3 F None F 0 Agg CureAmitriptylineto aggressor: yes/no 1/23 1/17

17 4 M None 6 M 0 Agg CureDiazepam to victim: yes/no 15/15 9/11

18 3 M Am 6 M None ? Cure Numbers in the cure/no cure categories represent individual cases. Only one comparison was significant19 5 F Bu ? Mand F None ? Cure20 F None 0.25 F None Agg Cure21 M Bu 3 M D Agg Cure frequency less than five, biologically reasonable categories were collapsed as needed.22 M Am 8 M None Agg Cure23 F None 10 F None Victim Cure All tests were two-tailed at a = 0.05.

24 M None 5 M and F 0 Agg Cure25 F None 3 F D Both Cure26 F Ovaban 0.25 M None Agg Cure 3. Results27 M None 3 F 0 ? Cure28 M Am 5 F 0 Victim Cure Seventy-seven cases of intercat aggression were treated between 1988 and 1994. Of29 M None M None Both Cure these cases, 50 owners could be located; all 50 were willing to participate in this study.30 6 M Am 9 M and F None Victims Cure31 3 F None M 0 ? No cure

Two cats had died before treatment could be initiated and were not included in the

32 M and F None 3 F 0 Agg No cure study. The number of cases cured was examined for the different sexes. Of 48 cases, 3033 M Bu/Am 7 M 0 Both No cure were considered cured, and 18 were not cured. Of the 'no cure' group. two cats were34 F None 2 F None Agg No cure euthanized, seven cats were given away, and nine cats remained in the home with35 M Bu II M 0 ? No cure permanent physical separation.36 5 M Bu M None No cure37 5 M Bu M D Agg No cure

All male cats and female cats had been castrated or spayed before the consultation. In

38 4 M None F None Victim No cure 43 of the cases of aggression, there was clearly one aggressor and one victim. Within39 II M None 12 F D Both No cure this group of cats. there was a significant difference from a 50:50 ratio in the proportion40 3 M None 6 F 0 No cure of cases in which a male cat (28 cases) vs. a female cat (15 cases) initiated the41 4 F None 0.58 F None Agg No cure aggression and was the sole aggressor (P = 0.05). There was no significant difference4:! 4 M Bu 4 M None Buth No cure among sex combinations of aggressor-victim pairs. Fifteen pairs consisted of a male4] M None 7 F D No cure44 M Bu F 0 Agg No cure45 5 M None 4 F None ? No cure46 I F None

158 £.M. Lindell el al. / Applied Animal Behaviour Science 55 ( J997) J53 - J62 EM. Lindell et al. / Applied Animal Behaviour Science 55 (J997J /53-/62 159

The number in parenthesis represents the number of cases in which clients who used a particular treatmentmodality also subjectively reponed that the modality seemed to facilitate treatment.

Tabl~ 3Number of cases of imer-cat aggression in which suggested treatment modalities were implemented out of the48 considered __ m T ~_m _~ __ n --- -- ... -48 considered

16(0)6(0)

5(0)

13{l)7(0)3(0)

No cure group (n ~ 18)

21(6)

11(4)

WU)22() I)7(2)4(3)

Cure group (11 = 30)Separation+ ReinforcementOdor exchangeMedicationCarrierBell

Treatment

M FSex of Aggressor

o , 5r

10C8 55

e8

N 30u

m 25.~ 2SD

; 20

Fig. I. Number of cases of aggression involving male (M) and female (F) aggressor cats. Whether theaggressor cat was a male or female did not affect the likelihood of cure.

M·M F·F M·F F·MPairs Fighting inHousehold

Fig. 2. Number of cases that were cured vs. not cured for aggressive pairs in household. The first initial in thepair represents the aggressor, the second represents the victim. For example, M-F represents a male aggressorand a female victim. The number of cures was not significantly different for anyone pair of sexes.

aggressor and a male victim, 13 pairs consisted of a male aggressor and a female victim,10 pairs consisted of.a female aggressor and a female victim, and five pairs consisted ofa female aggressor and a male victim.

There was no significant difference in the number of cures for male-initiated (18cures of 30 cases) vs. female-initiated (12 cures of 17 cases) aggression (Fig. I). One ofthe no-cure cases involved both a male and female aggressor and was not included inthis comparison. When fighting pairs were examined, excluding households with morethan two fighting cats, the number of cures was not significantly different for anyonepair of sexes (Fig. 2).

ISN 14u 13m 12b 11

e 10 'r 9

87654321o

• cure

lilno cure

For each of the six treatment suggestions, the number of households that tried aparticular suggestion was determined (Table 3). As the numbers of households that trieda bell or carrier was very low, these two treatment choices were not included in theevaluation of treatment efficacy. Whether households tried one treatment (10 cures of 15cases). two treatments (seven cures of 12 cases), or three and/or four treatments (12cures of 20 cases) did not affect the cure. One of the households in the cure group didnot try any suggested treatment method.

No one treatment resulted in a significantly greater number of cures than any other.However, some clients subjectively indicated that a particular treatment suggestionseemed to facilitate the treatment (Table 3). In addition, three clients in the 'cure' groupreported altemative treatments which they believed contributed to the resolution of theaggression. One client reported a beneficial effect of non-specific herbs. Anotherreported that her rolling the aggressor onto his side, in view of the victim, served todecrease aggressive displays. A third client felt that by repeatedly subjecting theaggressive cats to a situation that elicited a fear reaction from both cats, in this case a carride. she was able to reduce the aggression between the cats .

For the nine households which used medication as the only form of treatment, therewere seven cures. This cure percentage was not significantly different from thepercentage of cures in households that used other treatments with or without usingmedication (23 cures for 39 households).

The number of cures for cases in which victims received medication, either alone orin combination with other treatment modalities, was equal to the number of cures incases in which victims did not receive medication (each 15 cures of 24 cases). Therewas no significant difference in number of cures for households in which only theaggressor received medication (seven cures of 11 cases), only the victim receivedmedication (nine cures of 14 cases), both received medication (six cures of 10 cases), orneither received medication (eight cures of 13 cases). .

In 24 cases, diazepam was prescribed for the victim cats; in eightcases amitriptylinewas prescribed for aggressor cats; in 13 cases buspirone was prescribed for aggressorcats. Two aggressor cats received megestrol acetate; both were cured. The use ofdiazepam or amitriptyline was not significantly associated with cure or no cure. The use

J60 , E.M. Lindell et al.J Applied Animal Beluuiour Science 55 (1997) 153-162E.M. Lindell et al. / Applied Animal Behaviour Science 55 (/997) /53-/62 161

of buspirone wwas associated with significantly more treatment failures (five cures of 13cases, P = 0.0:05).

4. Discussion I

In this siudyfy, the aggressor cal of a fighting pair presented for treatment was morelikely lu be a mmale cal than a female cal. The aggression between cuts was equally likelytu be directed j rowurd a same sex or opposite sex victim. Thrs is in contrast tu thesituation in dogigs, in which a greater number of l 'USl:S of inter-dog aggression involvesame-sex pairss than mixed-sex pairs (Shennan et al ., 1996) . Clients arc frequentlyadvised againstst intruducing a second mule dug into a household in which a male dugresides (Han atund Hart, I':Jg~O. Clients that plan to reside with more than one cat mightbe advised io c consider that, as supported by the data presented. selecting a female calmight decrease e the likelihood uf problems with aggression in the future. However. wedo not have infeformarion on the sex distribution of al! households including those Wherefighting is nut (.J occurring,

An individuaial car's sociality, its tendency to cooperate with members of a group ofconspecifics, matay affect the likelihood of that cat existing peacefully within a multi-cathousehold, Therere may be a progressive increase in social behavior among domestic catsas they are Iororced into closer proximity by conditions of domestication than thattolerated by theieir solitary progenitors, It is possible that this increasingly social domesticcal may nut haave had sufficient lime to develop a complex means of communicationthrough subtle ~ gestures. As such. there may be a tendency for aggressive encountersrather than the t, threats and displacement which replace overt aggression in more sociaJspecies such as c dogs (Bon:heit and Veith, 1996).

The social sy.ystem of modern domestic cats appears to be flexible, varying with thenature of the inddividual cats, as well as with environmental factors such as availability offood and shelter.r (Voith and Borchelt, 1996). Some individual domestic cats appear tospend most of th.heir time alone. whereas group-living cats may travel alone yet seek thecompany of certatain members of their social group when resting (Kerby and Macdonald,1988).

Early positive e interactions of a kitten with other kittens and adult cats may facilitatethe development it of a social cat that will adjust readily to living in a multi-cat household(Martin and Bateieson, 1988). The personalities of the cats within the household may alsoaffect the likelihciood of aggression. Feuver et al. ( 1996) determined that individual catsbehaved consisteiently with regard to many behaviural crucriu illduJing fear of cats andSociability tu carsts.

The tendency (' of all individual cat to behave dcrensi\'~ly appears to emerge within thefirst 30-50dHYs c uf life (Adamc~' ct al., 1(83) . A defensive l'at is likely to nee or hiss atanother householold cat, and this behavior might prccipuute attacks by another cal. Mostkittens are adopteted after this behavior has de\'elop~d. Al'l'l'SS to a reliable temperumen]test might allow : veterinarians to assess an individual killen's degree of defensivenessand its suitability y fur living within a multi-cat household. Analuguus tests are at present

used to evaluate puppies (Beaudet et al., 1994). The prognostic value of available tests isnot yet clear.

This study determined that no treatment suggestion or combination of treatmentsuggestions resulted in an increased likelihood of cure. Owner compliance appeared tobe similar for the cure and nu cure groups, with the largest percentage of owners tryingmedication and physical separation.

Medical irucrvemion is often relied upon to facilitate behavior modification in cats.The: bcnzodiazepines such as diazepam are GABA synergists. They are prescribedextensively fur their unxiolytic effects in humans. and Marder (1991) reported thatdiazepam was particularly useful for the treatment of fear-induced aggressive behaviorin cats. Side: effects include sedation, tolerance, paradoxical excitement, and hepatoxicity(Center et al., IlJ':Jo). The rationale fur prescribing diazaparn for the victim cats in thisstudy was to decrease their anxiety in an attempt to suppress their defensive flightresponse .

Antidepressants such as amitriptyline, fluoxetine, and clomipramine are frequentlyprescribed for the treatment of affective aggression (Overall. 1992; Dodman andShuster, 1994). Amitriptyline was selected as one drug of choice for the aggressor cats.It is a non-specific serotonin reuptake inhibitor that has the significant advantage ofbeing cost-effective, Increasing the level of serotonin in the central nervous system maydecrease offensive aggression in cats, much as it does in humans (Dodman and Shuster,1994), Side effects of amitriptyline may include mild sedation, hepatotoxicity, andcardiac arrhythmias (Overall, 1992).

Another anxiolytic drug, buspirone, has frequently been prescribed based on itsserotonergic activity with minimal side effects (Dodman and Shuster, 1994), Buspironewas prescribed to aggressor cats based on its two advantages: minimal risk of sideeffects and moderate cost. In this study, the use of buspirone was associated with adecreased probability of cure of intercat aggression. The actual behavior was notrecorded by the owners, However, administration of buspirone was not useful inobtaining a satisfactory outcome for the aggression. The use of diazepam or amitripty-line did nut appear to improve the outcome of the cases in this study.

One limitation of this study was the small sample size used to assess the effectivenessof the treatment options. For example, to detect the difference between 87,50/0 cure and57.5(./(; cure (for drugs used vs. drugs not used) as significant would have required 2.5times more cuts. (However, most proportions we compared were much closer to eachother and lacked practical importance-making sample size moot.) A second limitationis that with 18 comparisons used in this study. the apparent significance of the test forbuspirone could be due to chance. A third limitation wus that in this retrospective study,we relied 011 owner recall uf treatments used as well as of outcome.

A standurdized diagnostic classification scheme fur feline aggression should beadopted . General categories of intercat aggression have been described previously(Burchell and Veith, 1987; Chapman. 1':J91). A prospective study which includesanalysis of specific diagnostic and follow-up criteria would be useful. These criteriacould be used to establish both subjective and objective cure gruups. Owners could beasked to record numbers of episodes of aggressive displays and to rate the intensity ofthese displays. Although owner recall necessarily involves some loss of accuracy in data

fI.~,

~ rl'

~ ;

1:

retrieval. it is the owners' perspective that eventually determines whether the outcome ofa behavior problem is satisfactory or not. Through consideration of specific inclusionand exclusion criteria. the effectiveness of behavior therapy might be increased.

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APPLIED ANIMALBEHAVIOUR

SCIENCE

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(Editors). Readings in Companiun Animal Behavior. Veterinary Learning Systems, Trenton. NJ. pp,214-216.

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The behavioural and physiological responses offarmed red deer (Cervus elaphusi penned adjacent

to other species

S.M. Abeyesinghe a, PJ. Goddard a,., M.~. Cockram b• MacaulayLand Use ResearchInstitute,Craigiebuckler, Aberdeen.AB9 2QJ. UK

b Dept. VeterinaryClinicalStudies, Royal (Dick) Schooloj Veteritaary Studies, Universityof Edinburgh,VeterinaryField Station, Easter Bush.Roslin.Midlothian,EH2S 9RG, UK

Accepted 14 January 1997

Abstract

The experiment describes the implicationsof red deer (Ceruus elaphus) being kept in pens inclose proximity to other species as may occur during abattoir lairage. Twenty groups of five maleyearling red deer were used to study behaviouraland physiological responses over a 2-h period toone of five treatments: red deer penned adjacent to either an empty pen, unfamiliar red deer, cattleor pigs, and red deer which had previously been exposed to cattle (previously grazed adjacent tocattle) penned adjacent to cattle. Alert behaviour was significantly affected by treatment andgroups of red deer penned next to cattle spent more time being alert than when next to unfamiliarred deer (0.68 vs. 0.32 scans: P < 0.05). Red deer next to cattle or pigs tended to spend less timeidling than when next to an empty pen and engaged in more agonistic interactions over a 2-hperiod (15.6 and ~2.8 vs. 6.1 interactions per deer respectively; P < 0.001). When next to cattle orpigs, less lying was observed than when next to unfamiliar red deer and red deer were lessdispersed in the test pen. spending more time in areas furthest away from the alternative speciesthan in areas closest to them ( P < 0.001). Heart rates of red deer penned next to cattle (70.3 beatsper min (bpml), pigs (77.5 bprn) and unfamiliar red deer (72.1 bpm) were not significantlydifferent. Red deer previouslyexposed to cattle and pennednext to cattle and red deer penned nextto pigs had higher heart rates than those penned next to an empty pen (79.1 and 77.5 VS. 67.3 bpm;P < 0.01 and P < 0.05 respectively). Plasma cortisol concentratiqns in samples collected at

• Corresponding author. Tel.: + 44-1224·318611; fax: + 44-1224-311.556; e-mail:p.goddard@mluri.sari.ac.uk

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