Are multi-cat homes more stressful? A critical review of the evidence associated with cat group size and wellbeing.

The primary objective of this review was to conduct a systematic critical appraisal of published literature, in order to assess the evidence regarding the impact of cat group size on cat wellbeing in the domestic home. The secondary objectives were to: (i) identify additional social and environmental mediators of cat wellbeing in these contexts; and (ii) identify general limitations within the current evidence and provide recommendations for future studies. A systematic search of electronic databases (Scopus, Web of Science and Google Scholar) was conducted using targeted Boolean phrasing. Papers were retained for appraisal of full text where they included a comparison of both single (n = 1) and multi-cat (n ⩾2) domestic housing conditions and/or comparison of different multi-cat group sizes, within a single study, and where they compared outcome measures that were either behavioural and/or physiological and deemed as relevant indicators of cat wellbeing. A total of 1334 unique papers were returned, 15 of which were retained. Of these papers, only four stated their primary aim to be an investigation of links between cat group size and cat wellbeing. Overall, the reviewed papers did not indicate consistent directions of effects regarding cat group size and outcome measures relevant to wellbeing. This was similar for the other social and environmental mediators identified. Inconsistency in results is likely due to the substantial methodological variation, limitations in measures used as indicators of wellbeing and limitations in general study designs and reporting. Results also highlight the complex, multifactorial relationships between cat wellbeing and various social and environmental factors. These may be as, if not more, important than absolute numbers of cats residing within a household. Due to the various limitations and general paucity of research, further studies are recommended to provide a suitable evidence base regarding impacts of multi-cat living on cat wellbeing in domestic environments.