Behavioural observations of singly-housed grey short-tailed opossums (Monodelphis domestica) in standard and enriched environments.

The grey short-tailed opossum (Monodelphis domestica) has been used in biomedical research for over three decades. It is normally housed in standard rat cages and appears to have adapted well to captivity. Owing to their aggressive behaviour towards each other, adult males are normally housed singly and may spend considerable periods of time in social isolation. We wanted to carry out a preliminary study on the behaviour of singly-housed male short-tailed opossums in two different settings: a standard rat cage and an enriched floor pen. Five male opossums aged between 10 and 12 weeks were housed for seven days at a time in the two settings and their behaviour was filmed during the dark phase. Recordings were carried out on the first and the last night of housing, from 19:00 to 07:00 h, and all behaviours quantified according to an ethogram. All five males in this study showed stereotypic behaviours while housed in standard rat cages, but no such behaviours were seen when the animals were in the floor pen. In both cases, but very especially in the pen, animals spent less time active as the week came to an end. Some activities such as sniffing the air, manipulating the nest and, especially, interacting with the floor tube occupied the animals' time in the cage considerably more than in the pen. Conversely, the opossums spent considerably more time walking when inside the floor pen than when they were in the cage. The general trend with other activities such as eating, drinking or grooming was one of more time being devoted to them inside the cage than inside the floor pen, but the differences did not approach statistical significance. These findings suggest that single housing of short-tailed opossums in standard rat caging is detrimental to their welfare.