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Abstract

Objectives

The aim of the study was to analyse hair cortisol levels in cats whose owners had reported behavioural problems and undesirable behaviour. In addition, feline hair cortisol levels were compared between sexes, for indoor and outdoor cats and also for cats living in single or multi-cat households.

Methods

In total, 55 cats participated in the study, including 31 females and 24 males from various households. The cats belonged to 25 different owners who answered a questionnaire survey. The biological material used for the research were 2–3 cm fragments of hair removed at the level of the skin with scissors by the owners from the cats’ lumbosacral area. The cortisol concentration in the samples was determined with the DRG Salivary Cortisol HS ELISA. Statistical analysis of the results was performed with Statistica 13.3.

Results

A tendency toward lower cortisol levels was found in outdoor cats vs indoor cats (U = 251.5, P = 0.066). It was also found that the cats exhibiting behavioural problems (eg, house soiling [eliminating outside the litter box]) or aggressive behaviour towards household members had statistically significantly higher hair cortisol levels (U = 162.0 [P = 0.027] and U = 9.0 [P = 0.040], respectively).

Conclusions and relevance

High levels of stress in cats can affect their interactions with other cats and with humans. The incidence of undesirable behaviour was observed more frequently in indoor cats. Significantly higher cortisol levels were found in cats that eliminated outside the litter box or that showed aggression towards their owners.

Keywords

Stress indoor outdoor undesirable behaviour

Introduction

Stress-related changes in feline behaviour can be perceived as bothersome by owners. High levels of stress in cats, regardless of its origin, can cause changes in food intake, grooming, general activity, exploratory behaviour, facial marking and interactions with other cats and humans, as well as increased vocalisation, anxiety, urine spraying and aggressive behaviour.¹ In addition, high levels of stress also affect the physical health of cats. It has been proven that high stress levels increase the risk of respiratory disease,^2,3 gastrointestinal problems¹ and feline idiopathic cystitis.^4,5 Animals undergoing chronic stress are much more likely to have a negative attitude towards surrounding stimuli and events, and have poorer problem-solving skills. Prolonged exposure to cortisol, which occurs in chronically stressed animals, can have a toxic effect on areas of the brain involved in memory and lead to a loss of prior ability to deal with stressors.⁶

Many of the stress-related behaviours perceived by owners as behaviour problems are, in fact, coping strategies.⁷ Problematic feline behaviours often seen as abnormal are actually natural cat behaviours that are considered troublesome by their caregivers.⁸ Sometimes a management strategy to redirect these behaviours to more appropriate ones is successful enough to allow owners to cope with them. Nevertheless, a significant number of cats are still euthanased, abandoned or rehomed due to behaviours that owners deem unacceptable.⁹

The best evidence for stress in animals is provided by a combination of physiological and behavioural data.^10,11 One of the biological markers of stress is cortisol. Cortisol is synthesised in the adrenal cortex in response to activation of the hypothalamic–pituitary–adrenal (HPA) axis.¹² Exposure to stressors is commonly associated with increased HPA axis activity; therefore, increased cortisol is an indicator of stress.¹³ One of the first studies that looked at measuring endogenously produced steroid hormones in hair was by Yang et al.¹⁴ Hair analysis for endogenously produced cortisol in humans was first documented by Raul et al.¹⁵ Since then, it has been repeatedly confirmed that the analysis of cortisol in hair is a unique tool allowing for non-invasive measurement of long-term HPA axis activity. Therefore, it can be considered an objective measure of chronic stress, both in humans^16–18 and animals.^19–21 Moreover, hair sampling is a non-invasive and painless way of collecting samples. The procedure is simple and the sample can be taken by a non-professional.¹²

The main aim of the present study was to analyse hair cortisol levels in cats whose owners had reported problematic and undesirable behaviours. In addition, feline hair cortisol levels were compared between sexes, indoor and outdoor cats and cats living in single or multi-cat households.

Materials and methods

Fifty-five cats participated in the study, including 31 females and 24 males from different households. All were kept as companion animals. The cats were receiving food that was compliant with the European Pet Food Industry Federation standards. The health status of all cats was confirmed based on a normal complete blood count, serum biochemistry and urinalysis results, as well as regular antiparasitic prophylaxis and vaccinations. Fifty animals were neutered (the surgery was performed at least 6 months prior to the examination) and five were intact. The cats were divided into three age groups: <3 years old (n = 14); 3–10 years old (n = 29); and ⩾11 years old (n = 12). Twenty-seven cats were obtained by adoption, seven had been purchased from breeders and the owners of the other 21 specified their origin as ‘different’ (eg, received as a gift or found outside). More than half of the studied cats were indoor-only (n = 31). In eight cases, the cats were the only cats in the household; in all other cases there was more than one cat in the house. Moreover, each cat (both from a multi-cat and single-cat households) shared space with at least one dog.

The cats belonged to 25 different owners who were presented with an original questionnaire survey. The first part of the questionnaire concerned basic information about the cat, such as sex, age and origin. The second part referred to selected undesirable behaviours or behavioural problems in cats: elimination of urine or faeces outside the litter box/marking with urine or faeces; attacking the hands or legs of the handler during play; aggressive behaviour towards household members; aggressive behaviour towards other animals in the household; and excessive licking, furniture scratching, vocalisation, night races/increased night-time activity and consumption of inedible objects (eg, cardboard, plastic bags, etc).

The biological material used for the research was hair samples collected by the owners from the cats’ lumbosacral area. It was performed with scissors (non-invasive) and a 2–3 cm fragment of hair was cut at the skin level. The samples were then placed in a foil bag, appropriately signed and labelled, and stored at room temperature until analysis.

The extraction methodology was modified from Koren et al²² and Accorsi et al.²³ The length of hair used for the analysis was 1 cm, measured from the root, as average cortisol exposure for a 1- or 2-month period can be measured in segments of 1 or 2 cm in length, respectively.²⁴ In total, 20 mg of hair samples were prepared. The cortisol concentration levels in the samples were determined with the DRG Salivary Cortisol HS ELISA. The procedures followed the manufacturer’s instructions. Cortisol concentrations were evaluated in ng/ml.

The statistical analysis of the research results was performed with Statistica 13.3. To describe the distributions of the examined features, the mean, SD, median, range and interquartile range were established. The analysis evaluated the significance of differences in cortisol levels in the tested animals depending on sex, origin and home conditions, and was performed with the Mann–Whitney U-test when comparing two groups and the Kruskal–Wallis test when at least three groups were being compared.

Results

No significant relationship between feline cortisol levels and sex (P = 0.993), neutering (P = 0.599), age (P = 0.850) and the cat’s origin (P = 0.471) was found in the present study (Table 1).²⁵

Table 1

Hair cortisol levels in the 55 participant cats by sex, age, origin, neutering and outdoor access

Variable	Group	n	Mean ± SD	Median	Mann-Whitney U-test (U) or Kruskal–Wallis (KW)	P value
Sex	Female	31	0.477 ± 0.456	0.333	371.0^(U)	0.993
Sex	Male	24	0.410 ± 0.181	0.338	371.0^(U)	0.993
Neutered	Yes	50	0.448 ± 0.375	0.330	106.5^(U)	0.599
Neutered	No	5	0.446 ± 0.192	0.435	106.5^(U)	0.599
Age (years)	<3	14	0.387 ± 0.155	0.342
	3–10	29	0.500 ± 0.464	0.413	0.354^(KW)	0.850
	⩾11	12	0.393 ± 0.222	0.322
Origin	Adopted	27	0.464 ± 0.477	0.307	1.506^(KW)	0.471
	Purchased from a breeder	7	0.446 ± 0.309	0.279
	Other	21	0.427 ± 0.164	0.375
Outdoor	Yes	24	0.355 ± 0.150	0.310	251.5^(U)	0.066
Outdoor	No	31	0.522 ± 0.453	0.435	251.5^(U)	0.066

Outdoor and indoor cats

Based on the conducted research, a tendency towards lower cortisol levels was observed in outdoor cats vs indoor cats (U = 251.5; P = 0.066) (Table 1).²⁵ Behavioural problems and undesirable behaviours were more often reported in indoor cats than their outdoor counterparts (Figure 1). One-third (32%) of indoor cats in this study showed inappropriate elimination (urinating and/or defecating) outside the litter box, 23% scratched furniture at home and 16% showed increased activity during the night, excessive vocalisation, aggression towards other animals and attacking owners while playing (Figure 1).

Figure 1

Occurrence of behavioural problems in indoor and outdoor cats

Number of cats in the household

Hair cortisol levels were not affected by the number of cats living in the household (P = 0.636; Table 2).

Hair cortisol levels and the occurrence of behavioural problems and undesirable behaviours

No significant relationship was found between hair cortisol levels in cats and attacking the handler during playtime, aggressive behaviour towards other animals, excessive licking, furniture scratching, night-time hyperactivity, persistent vocalisation or the consumption of inedible objects (Table 2).

Table 2

Feline hair cortisol levels in the 55 participant cats in relation to the occurrence of undesirable behaviours and behavioural problems

Variable	Group	n	Mean ± SD	Median	Mann-Whitney U-test (U) or Kruskal–Wallis (KW)	P value
Excretion of urine or faeces outside the litter box/marking with urine or faeces	Yes	13	0.484 ± 0.147	0.469	162.0^(U)	0.027*
	No	42	0.437 ± 0.406	0.308	162.0^(U)	0.027*
Attacking the hands or legs of the handler during play	Yes	8	0.444 ± 0.272	0.362	182.5^(U)	0.898
Attacking the hands or legs of the handler during play	No	47	0.449 ± 0.377	0.333	182.5^(U)	0.898
Aggressive behaviour towards household members	Yes	2	0.822 ± 0.294	0.822	9.0^(U)	0.040*
Aggressive behaviour towards household members	No	53	0.434 ± 0.358	0.327	9.0^(U)	0.040*
Aggressive behaviour towards other animals in the household	Yes	7	0.511 ± 0.272	0.436	130.5^(U)	0.351
Aggressive behaviour towards other animals in the household	No	48	0.439 ± 0.374	0.327	130.5^(U)	0.351
Excessive licking	Yes	2	0.639 ± 0.288	0.639	22.0^(U)	0.194
Excessive licking	No	53	0.441 ± 0.364	0.327	22.0^(U)	0.194
Furniture scratching	Yes	9	0.358 ± 0.258	0.279	149.0^(U)	0.194
Furniture scratching	No	46	0.465 ± 0.378	0.414	149.0^(U)	0.194
Persistent vocalisation	Yes	9	0.448 ± 0.186	0.438	171.5^(U)	0.426
Persistent vocalisation	No	46	0.448 ± 0.388	0.327	171.5^(U)	0.426
Night-time hyperactivity	Yes	6	0.823 ± 0.959	0.367	121.0^(U)	0.501
Night-time hyperactivity	No	49	0.402 ± 0.177	0.327	121.0^(U)	0.501
Consumption of inedible objects	Yes	2	0.228 ± 0.062	0.228	17.0^(U)	0.121
Consumption of inedible objects	No	53	0.456 ± 0.365	0.360	17.0^(U)	0.121
Number of cats in thehousehold	1	8	0.399 ± 0.283	0.282	2.547^(KW)	0.636
	2	16	0.396 ± 0.163	0.359
	3	12	0.563 ± 0.694	0.322
	4	12	0.410 ± 0.163	0.429
	7	7	0.490 ± 0.199	0.413

P <0.05

The study showed that statistically significantly higher hair cortisol levels (U = 162.0, P = 0.027) were found in cats that eliminated outside the litter box compared with cats whose owners had not reported such problems (Table 2).^8,25 Additionally, in cats showing aggressive behaviour towards household members, statistically significantly higher hair cortisol levels were also observed, compared with individuals not showing such a behaviour (U = 9.0, P = 0.040) (Table 2).

Discussion

No statistically significant relationship between feline cortisol levels and sex, neuter status, age and origin were found in the present study. Similarly, no statistically significant differences in the levels of cortisol in the hair of cats according to sex (P = 0.67) and neuter status (P = 0.62) were found by Contreras et al.²⁵ Moreover, no statistically significant differences in the levels of hair cortisol according to indoor/outdoor status (P = 0.38) were reported in the same study.²⁵ However, in the present study, a tendency towards lower cortisol levels in outdoor cats vs indoor cats was observed.

The difficulty in adapting to an indoor-only life can be related to the fact that the domestic cat as a species has not been selectively bred for companion animal traits, nor for living in confinement, in close proximity to people.⁸ As shown by data from the USA, >90% of household cats are mixed-breed cats that do not come from breeders and do not have a documented pedigree, so they probably come from free-roaming or stray populations, indicating that their early socialisation process – as far as contact with people is concerned – may be impaired.8 Furthermore, the indoor environment often lacks the most important elements for cats to exhibit their natural behaviours. An improperly managed environment, and insufficient number and quality of resources necessary for the cat’s welfare can contribute to chronic stress, which manifests itself in elevated cortisol levels. However, outdoor cats are better able to exhibit species-typical behaviours in environments richer in stimuli and resources, but it should be noted that outdoor cats are exposed to many dangers, including fights with conspecifics, traffic accidents, infectious diseases and getting lost.⁸

In both social and non-social animals, the frequency and type of interaction with conspecifics can affect HPA axis activity.²⁶ However, in the present study, hair cortisol levels (P = 0.636) were not affected by the number of cats in the household (Table 2). No differences in cortisol levels according to the number of cats in a household (P = 0.21) were found by Contreras et al.²⁵ Faecal glucocorticoid metabolites in singly and group-housed cats were compared by Ramos et al,²⁷ who found no significant differences in the levels of faecal glucocorticoid metabolites according to the number of cats in the household. Broadley et al reported no significant differences in Cat Stress Score results for cats from single-cat households and cats from multi-cat households (P = 0.18).²⁸ The social structure of domestic cats is flexible, ranging from solitary life to group life; however, flexibility in the social structure depends mainly on the availability of food.⁸ Moreover, as suggested by Ramos et al,²⁷ other environmental aspects within the households themselves (eg, relationship with humans and resource availability) may play even more important roles in feline stress levels than the number of cats itself.

In the present study, statistically significantly higher hair cortisol levels were found in cats that eliminated outside the litter box. Hair cortisol levels were also statistically significantly higher in cats with litter box problems (P = 0.02), according to Contreras et al,²⁵ urinating and defecating outside the litter box can be influenced by a number of underlying factors. It can be difficult for cat owners to distinguish between inappropriate elimination and territory-marking. Urine spraying is considered to play a crucial role in territorial marking and can be triggered by a strong territorial instinct. Another sign of territorial behaviour can be defecation in visible places outside the litter box. Moreover, elimination behaviour can be affected by environmental and social factors, as well as underlying health problems.⁸ Family changes (eg, new household members), poor litter box management or the owner’s absence (separation anxiety) can contribute to chronic stress and thus to urine-marking behaviour.^29,30

In the present study, significantly higher hair cortisol levels were found in cats that showed aggressive behaviour towards human household members. A similar positive correlation between agonistic behaviour and hair cortisol levels in female cats was reported by Finkler and Terkel,²⁹ indicating higher hair cortisol concentrations in aggressive cats. Significant correlations between aggression and high cortisol levels are often found in intact cats and dogs. High levels of cortisol and aggression are also associated with social position and dominance status.^31,32 A similar hierarchy model is not seen in domestic cats; however, living in an inadequately managed environment can lead to competition over resources and territorial conflicts. The above, together with frustration caused by inability to exhibit natural behaviours (frequent in indoor cats), can contribute to chronic stress and manifest itself in aggression.

Conclusions

A tendency towards higher levels of cortisol in indoor cats vs outdoor cats was observed in this study. A higher prevalence of undesirable behaviours in indoor cats was also reported, with inappropriate elimination (urinating and/or defecating outside the litter box), furniture scratching or night-time hyperactivity being the main causes of complaint among owners. Significantly higher cortisol levels were found in cats that eliminated outside the litter box or showed aggression towards their owners. Nevertheless, it should be noted that individual responses of cats to particular stressors may vary.

Footnotes

Acknowledgements

I wish to express my gratitude to Professor Aneta Strachecka for her invaluable help in performing the laboratory analyses.

Accepted: 26 December 2022

Conflict of interest

The authors declare no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The research was part of a research project for young scientists (ZKE/MN-6/ZIR/20), University of Life Sciences in Lublin, Poland.

Ethical approval

The work described in this manuscript involved the use of non-experimental (owned or unowned) animals. Established internationally recognised high standards (‘best practice’) of veterinary clinical care for the individual patient were always followed and/or this work involved the use of cadavers. Ethical approval from a committee was therefore not specifically required for publication in JFMS. Although not required, where ethical approval was still obtained, it is stated in the manuscript.

Informed consent

Informed consent (verbal or written) was obtained from the owner or legal custodian of all animal(s) described in this work (experimental or non-experimental animals, including cadavers) for all procedure(s) undertaken (prospective or retrospective studies). No animals or people are identifiable within this publication, and therefore additional informed consent for publication was not required.

ORCID iD

Justyna Wojtaś

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Hair cortisol levels in cats with and without behavioural problems

Abstract

Objectives

Methods

Results

Conclusions and relevance

Keywords

Introduction

Materials and methods

Results

Outdoor and indoor cats

Number of cats in the household

Hair cortisol levels and the occurrence of behavioural problems and undesirable behaviours

Discussion

Conclusions

Footnotes

Acknowledgements

Conflict of interest

Funding

Ethical approval

Informed consent

ORCID iD

References