Effects of early social separation on the behaviour of kittens of the domestic cat

For many mammals the presence of the mother and/or siblings is an important component of an individual's early developmental environment, and lack of these social influences can have long-lasting effects on morphological, physiological, and behavioural development. Surprisingly, little is known about the effects of premature maternal and sibling separation in the domestic cat, even though hand-raising is rather common due to the large number of orphaned and rescued kittens. In this study we assessed 62 nine-week-old kittens (32 mother-reared, 14 orphans hand-raised with siblings and 16 hand-raised orphan singletons) in three behavioural tests: a handling (struggle) test, a food defence (meat) test, and a separation/confinement test. Additionally, we used infrared thermography to evaluate stress-induced changes in eye and nose temperatures in the separation/confinement test. We found no differences in body weight between groups at weaning at 9 weeks of age, but we found behavioural differences between the control and the two orphan groups in all three tests. Compared to control, mother-reared kittens, orphans raised with siblings and orphan singletons struggled sooner in the struggle test, plus vocalised more and exhibited greater locomotor activity in the separation/confinement test. In the meat test, only the orphans raised with siblings, but not the singletons, started consuming the raw meat stimulus sooner than control individuals. Facial thermography showed a general trend for eye and nose temperatures to decrease in response to the separation/confinement test, with no differences between rearing conditions. Our findings show that the early social environment is influential in shaping the long-term behaviour and physiology of kittens. The behavioural differences between mother-reared and hand-raised individuals should be considered for the well-being of the animals when fostering and during the adoption process. Our results suggest that, as expected, developing without the presence of the mother and raised by humans (with or without siblings) has an effect on the behaviour of kittens to weaning age and possibly even into adult life.