Table 1.

Summary of appraisal of the six papers meeting the inclusion criteria of assessing single versus multi-cat environments on physiological and behavioural measures of stress in confined domestic cats

Author, date and title	Uetake and others [30]	Lichtsteiner and Turner [31]*	Gourkow N, Fraser D [34]	Ottway, D. S. & Hawkins, D. M. [33]*	Kessler M. R. & Turner D C. [35]	Kessler M. R, & Turner D C. [32]
	Effects of single caging and cage size on behavior and stress level of domestic neutered cats housed in an animal shelter [30]	Influence of indoor-cat group size and dominance rank on urinary cortisol levels [31]	The effect of housing and handling practices on the welfare, behaviour and selection of domestic cats (felis silvestris catus) by adopters in an animal shelter [34]	Cat housing in rescue shelters: A welfare comparison between communal and discrete-unit housing [33]	Socialization and stress in cats (felis silvestris catus) housed singly and in groups in animal shelters [35]	Stress and adaptation of cats (felis silvestris catus) housed singly, in pairs and in groups in boarding catteries [32]
Study design	Randomised controlled trial	Controlled trial	Randomised controlled trial	Cohort	Randomised controlled trial	Cohort
Stated aim of paper	• To provide information on the minimum spatial requirement for singly caged cats in animal shelters	• The relevant aim was to determine “whether the urinary cortisol levels of the cats are related to environmental parameters…additionally the cortisol levels of cats from private households were compared with shelter cats to check for an influence of location”	• To examine how different housing and handling conditions affected the welfare, behaviour, adoption rate and selection of individual cats by adopters	• To test the hypothesis that, in long-term shelter care, cats housed communally with unfamiliar conspecifics experience higher levels of stress than do cats housed in discrete units, due to inappropriate and unstable social grouping	• To provide recommendation for the most suitable housing type for cats with known socialization status	• To investigate levels of stress in cats housed singly, in pairs and in groups
						• To compare stress levels in newly arrived cats to a longer-term control group
Subjects	• 6 cats between 2–15 years old residing in an animal shelter	• Twenty-one shelter cats	• 165 cats entering an animal shelter	• 74 cats residing in 2 animal shelters, randomly selected from the shelter population	• 169 cats between 1–8 years old residing within an animal shelter	• 140 cats between 1–15 years old, residing in a boarding cattery in 2 categories, plus a “control” group of 45 un-owned cats
		• All cats had lived in the shelter for at least 3 weeks and were considered “adoptable”	• Inclusion criteria: mixed breed, 1–7 years of age, neutered, healthy
			• Excluded: feral cats
				• Excluded: cats having been in the shelter < 1 month
						• Excluded: ill cats, “highly stressed” cats (in “control” group only)
Environment prior to study	• All cats had previously been kept in a socially stable group environment for at least 7 months	• All cats had been in the shelter for at least 3 weeks	• Cats were from both stray and domestic home environments (numbers of each not specified)	• Cat were from both stray and domestic home environments (numbers of each not specified) and had been in the study environment for a least 1 month	• All cats were relinquished/unwanted (no history of previous long-term living experiences)	• 140 cats were owned, from single or multi-cat homes
		• Single housed cats were transferred to single housing at least one week before sampling
	• No history of background prior to this 7 month period
						• Origin of 45 “control” shelter cats not specified.
					• Cats in the single cage condition had previously been housed singly for 10–20 days in the study environment
			• The study commenced on day one of exposure to the study environment for all individuals
						• 85-87% of the owned cats had been exposed to the study environment on a previous separate occasion
					Cats in the group condition had previously been housed in a group with changing compositions for 10–20 days in the study environment
						• Control cats had spent between 2 and 16 weeks in the study environment
Intervention/group definition	• All individuals were exposed either to small, medium or large single cages in varying orders, all without human social contact. This was compared with their baseline stress levels when previously group housed (it is assumed the group size at this point was six)	• Two groups, comprising six and seven cats housed communally	• Assigned to one of four housing conditions:	• In one shelter, individuals were already housed communally in one of three groups (either 33, 47 or 65 individuals per group)	• Cats housed in individual units or in a group enclosure (specific group sizes unspecified but at least >5)	• Boarding cats housed singly (60), in pairs (40) or groups (40) (each group size unspecified but at least >2) according to owner preference
			- basic single (minimal human interaction)
		• Four of these group-housed cats were removed from each group and housed singly for one week prior to being sampled
			- enriched single (with consistent human handling and human interaction)
			- basic communal (eight cats per group), with consistent human handling and human interaction
						• “Control” cats (45) were living in six groups (size unspecified), which had been stable and un-altered for at least 2 weeks prior to the study
				• In the other, 12 cats were housed in pairs and nine cats were divided into threes. These cats were previously socialised together or siblings. Additionally, 15 cats were housed singly
			- enriched communal (eight cats per group), with consistent human handling and human interaction and extra hiding places and toys
Outcome measures (refer to Table2for further information on measures)	• Urinary cortisol: creatinine ratios	• Urine cortisol: creatinine ratio on a single voided sample	• Cat Stress Scores (CSS)	• CSS scores and time budgets (including eat, drink, groom, play, rest, stereotypic behaviour and agonistic encounters)	• CSS	• CSS taken 4 x daily
					• Human-Approach-Test (HAT), Cat-Approach-Test (CAT) and socialisation questionnaire used to determine whether cats were socialised towards conspecifics or humans
			• Outcome of stay i.e. adopted, not adopted, euthanized or isolated for physical health reasons
	• Behavioural time budgets (including resting, drinking, eliminating, vacuum behaviour, and others, locomotion, social/solitary play, exploring and self-grooming)
			• Time to adoption
Data collection period and frequency of relevant measures taken to assess stress.	• Cats were exposed to each condition for six days, i.e. the study period was a total of 18 days	• A single urine sample was taken for each cat on a convenience basis during the study period (14 days).	• The study period lasted 21 days	• Data on individuals was collected each day over 15 consecutive week days, however, it is unclear if all cats were sampled for full duration due to cat turnover during the study period	• Data collected over a 7 day period	• Data collected over 14 days
			• Cats were observed for 2 minutes each day, and assigned a Cat Stress Score for the first 10 days of the study period, however, not all cats were assessed for the full 10 days
					• Cat-Stress-Score was assessed every l0 minutes during the first hour post placement into the test condition, then twice (within a 15-min interval) after 6 hours. For the following days, 2 observations were made in the morning and 2 in the evening	• CSS were initially recorded after the first two hours of entry into the test environment and were then taken 4 times daily, each day, twice in the morning and twice in the evening
	• Behavioural observations made over 3 hours during the last 2 days in each of the different housing conditions
	• Urine samples were collected in the morning and evening of each day and then averaged, repeated each day of the study period
				• Cats instantaneously scan sampled and assigned a CSS each day, every 30 minutes from 08:30 am to 15:30. All other behavioural data was collected via one–zero sampling in between each scan interval
					• HAT and CAT randomly assessed twice a day for 4 days across the test population, once in the morning and once in the evening
Key results	• Time spent in locomotion and solitary play were lower in individual cages than in group housing conditions	• Urinary cortisol:creatinine ratios were highly variable	• CSS were highest in the basic single housing treatment	• No differences in CSS scores were found between cats housed individually and those housed with either one or two other familiar cats	• Cats that were considered non-socialised with people had higher CSS levels than those considered socialised, irrespective of housing type	• The highest reduction in CSS scores occurred between the first and fourth and first and fifth days within the boarding cattery
			• These cats also had the lowest adoption rate.
	• Urinary cortisol: creatinine ratios were higher in singly housed cats (not statistically significant)	• No statistically significant differences between groups
			• No significant differences noted between other housing conditions
					• Where cats were considered socialised to other cats, CSS did not differ between single and group housing
						• “Control” group cats had significantly lower stress levels than boarding cats
				• Overall CSS scores were higher in cats housed communally than cats housed in discrete units alone or with previously familiar conspecifics Highest scores were only seen in communal housing**
					• Those considered non-socialised to conspecifics had higher CSS than those which were socialised to conspecifics, when housed in groups	Housing type did not appear to influence CSS in boarding cats
					• Cats considered non-socialised to conspecifics had lower CSS during the first hour of the study and on the last two days when housed singly compared with group housing
				• Play and resting/sleeping in close contact with conspecifics were observed in more instances in cats housed in pairs or threes than in communal housing**
					• Group housed cats had higher CSS when a cat considered non-socialised to conspecifics entered the group, compared to when a cat considered socialised with conspecifics entered
				• Agonistic encounters were observed in more instances in communal housing than in discrete--unit housing**
Conclusion	• The experience of cats being exposed to a rotation of individual cages of varying sizes for 18 consecutive days (6 days in 3 different cages) appears to be more physiologically stressing than when they are housed in a familiar group environment, with no intervention	• Group versus single housing did not result in a significant difference in cortisol: creatinine ratios	• Cats in barren single housing had higher stress levels than cats in the other 3 housing types and lowest adoption rates	• Whether cats are housed individually or with one to two other familiar conspecifics does not appear to differentially affect stress levels	• Cats which have not been previously socialised to humans may find the shelter environment more stressful than those accustomed to humans	• Cats appeared to find an established colony environment to be less stressful than any of the boarding environments, whether single or group housed with novel or familiar conspecifics
					• Cats which are not successfully socialised to conspecifics may find group housing more stressful than those socialised to conspecifics
				• Housing cats in large groups appears to be more stressful than housing cats in discrete units (1–3 individuals in a single unit)**
						• Suggests that the novelty of the environment may be associated with a stress response
Main limitations	• No sample size calculation, but sample size very small.	• No sample size calculation, but sample size very small.	• No sample size calculations	• No blinding of observer	• No sample size calculations	• No sample size calculation
			• No blinding of observer
				• Non-random assignment of cats to groups
						• No blinding of observer
					• No blinding of observer
						• Comparisons made between two very different types of cats
	• No blinding of observer
					• Randomisation method not described
			• Insufficient detail to determine if groups were comparable at baseline
	• Randomisation methods unclear	• No blinding of observer
					• Sample size relatively small considering 8 sub-groups analysed	• The single and pair housing enclosures were less enriched than the group housing enclosures, which could have confounded the results
				• “Discretely-housed” cats could be housed singly, or in twos or threes with other cats they were previously socialised to. This limits the extent to which such comparisons meet the criteria of this CAT
			• Randomisation method not specified
	• Inappropriate comparisons used – stable enriched social group versus relatively barren single housing with minimal human contact	• No detail of how cats were assigned to groups
			• Groups not treated equally – all but basic single received extra human interaction causing potential confound
					• The validity of Cat-Approach and Human-Approach-Tests is questionable based on the methods used, (Non-conformity between the two different measures used to assess whether cats were socialised with conspecifics and with humans led to 30% of individuals being excluded from the data analysis)
		• Single cortisol: creatinine measure of uncertain significance
	• Stress measures may have related to barren environment/ frequent changes to housing conditions, especially in cats accustomed to a stable group housing situation		• Validity of the CSS as a measure of ‘Stress’ in cats (see Table 2)
						• Excluding individuals that were ‘highly stressed’ a potential confounder
		• Singly housed cats may have had an increase in cortisol due to having had a change in environment a week previously
			• No physiological measures considered
						• Validity of the CSS as a measure of ‘Stress’ in cats (see Table 2)
						• No physiological measures considered
				• Total residence time of each individual within the shelter prior to study not accounted for but could have acted as a confounder if not appropriately controlled for
					• No physiological measures considered
				• Cats were in two different shelters - the external environment varied between each group
				• Cat density per unit varied considerably in the discrete unit housing depending on whether there were 1,2 or 3 individuals housed together, whereas density was more consistent between communally housed groups
				• Cats had already had one month to acclimatise to shelter environment prior to sampling – external validity
				• Behavioural time budgets potentially a crude form of measurement to assess stress
				• No physiological measures considered
		• Main aims of this study were not related to the topic of the CAT
	• Behavioural time budgets potentially a crude form of measurement to assess stress

*The primary aims of this study were unrelated to the CAT question. However, a small sub-component of the study was relevant, and the critical review refers only to this portion.

**This portion of the study relates to comparisons that did not meet the inclusion criteria of the CAT due to the way that data was concatenated prior to statistical comparison. Such results are however included because they are considered otherwise highly relevant to the topic of the CAT