Cortisol levels and aggression in neutered and intact free-roaming female cats living in urban social groups

Free-roaming domestic cats in urban areas often live in defined social groups, and the breeding females in these groups tend to form structures of a matrilineal nature. In recent years, resulting from the growing populations of free-roaming cats in many cities worldwide, these cats are being managed using the Trap-Neuter-Return (TNR) method. The aims of this study were to explore the hypotheses that (a) neutering reduces aggression in the females living in such social groups; and (b) if such reduction does occur, that it might be accompanied by a reduction in cortisol levels. The study was conducted on eight cat feeding groups in residential neighbourhoods in Tel Aviv, Israel. The municipal veterinary department offers TNR services upon request. Cats are collected from the feeding group and returned to their original group after neutering. We found that neutered females showed reduced aggressiveness as well as reduced cortisol levels compared to the intact females. In addition, those intact females that displayed more aggression had higher cortisol levels compared to the less aggressive intact females. Based on the results of this study it is possible to suggest for the first time a possible relationship between cortisol levels and aggression in free-roaming female domestic cats. This study is an initial step in assessing the long-term effects of Trap-Neuter-Return (TNR) on the welfare of the individual cat. If cortisol levels in female cats are reduced after neutering, partly as a result of reduced social and reproductive pressures (as expressed by lower aggression of the neutered females), it is possible that TNR has an added beneficial role in cat welfare in addition to that of control of population size.