The effects of resource distribution on behaviour in pair housed silver fox vixens ( Vulpes vulpes) subsequent to mixing

Abstract

In nature, the way essential resources are distributed is recognized as a potentially important factor influencing the frequency of aggressive interactions between animals. This knowledge is rarely taken into consideration when designing housing environments for social groups of farm animals. Adult farmed silver foxes ( Vulpes vulpes) are often housed singly, but previous studies have demonstrated that vixens show a motivation for social contact in particular periods of the year and housing in social groups may therefore act as an alternative housing procedure for foxes. However, grouping unfamiliar animals may result in elevated levels of aggression due to competition for resources and thus affect welfare negatively. In the present study we investigated how housing environments with the same space and resources, but with different resource distributions affected the behaviour of adult vixens housed in pairs. A total of 40 vixens were housed in pairs in two coupled cages (2.00 m × 1.10 m × 0.75 m) with either two nest boxes and two food trays (treatment 1) or one nest box and one food tray (treatment 2) from 18 months of age. The occurrence of aggressive behaviour, play behaviour and synchronous resting was recorded throughout the day (i.e. every third hour for 15 min during 24 h) on day 1, day 5, day 19 and day 33 after mixing. In addition, the frequency of physical aggression was recorded for 75 min around feeding time. Body weight gain and wounds were also recorded on day 25 after mixing. The results showed that there had been more severe aggression in treatment 2 during the days after mixing due to higher frequency of physical aggression around feeding time (treatment 1: 0.6 ± 0.21 times, treatment 2: 2.9 ± 0.99 times, P = 0.06), more wounds (treatment 1: 3 of 10 pairs, treatment 2: 8 of 10 pairs, P = 0.03) and less body weight gain ( P = 0.03) compared to treatment 1. The observed aggression levels throughout the day decreased with subsequent observations days for both aggressive displays ( P < 0.01) and chase behaviour ( P = 0.04), indicating that it takes between 5 and 19 days to establish a stabile social relationship within a vixen pair. There was an increase in social ( P = 0.09) and locomotor play ( P = 0.03) as well as synchronous resting ( P < 0.001) with subsequent days after mixing, suggesting that the stress by being mixed with an unfamiliar conspecific is decreasing with time. In both treatments, there was a decrease in object play ( P < 0.001) with subsequent days after mixing, however vixens in treatment 2 showed in general more object play than vixens in treatment 1 (4.3 ± 0.60 scores vs. 2.5 ± 0.47 scores respectively). To conclude, we found that different resource distributions affected wounds, body weight gain and physical aggression during feeding in pair housed silver fox vixens. The elevated aggression levels the first days after mixing may affect vixens’ welfare negatively, however, the increase of social play after mixing suggests that social housing also have positive effects on welfare. The resource distribution of highly valued resources should be taken into account when designing the future social housing system for farmed foxes.