Agricultural and Food Science in Finland 149 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 9 (2000): 149–155. © Agricultural and Food Science in Finland Manuscript received September 1999 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 9 (2000): 149–155. Short term behavioural consequences of denied access to environmental facilities in mink Claus Peter Bjælke Hansen and Leif Lau Jeppesen Zoologisk Institut, Københavns Universitet, Tagensvej 16, DK-2200 København N, Denmark, e-mail: cpbhansen@zi.ku.dk The aim of this study was to investigate whether farm mink denied access to water for swimming became more frustrated than animals denied access to an empty cage. Also the relative importance of water for swimming, the empty cage and the nest box was measured. Seventy-eight farm mink were placed in four groups according to a 2x2 experimental design: two unit sizes, large and small, and two water conditions, with or without water. Each unit consisted of three cages side by side in which half of the animals had a water filled basin and the other half an empty area in the middle cage. This cage had openings to the other two cages. In addition, a tunnel above the basin connected the right and left cage. One hour before the beginning of daily observations the animals had their access re- stricted to only the left cage. Each animal was observed ten times a day on nine consecutive days. No difference in scratching into the tunnel, basin or nest box was detected between the four groups. All groups scratched significantly or nearly significantly more into the nest box than into both the tunnel and the basin. Most stereotypies were found in the group in small cages with a dry basin. Our investigation suggests that when compared to the deprivation from a nest box, the deprivation of water for swimming does not alone cause frustration of farm mink any more that the exclusion from an empty cage. However, it does indicate that the cage size may affect the level of stereotypy. Key words: welfare, stereotypy, swimming, deprivation Introduction The needs of a domesticated animal may not be relevant to its fitness but are relevant to its wel- fare because they involve a strong motivation (Weary and Fraser 1995). The Motivation for cer- tain behavioural patterns may be so strong that if their expression is not allowed the welfare of the animal may be jeopardized (Duncan 1998). That is why behavioural needs should be con- sidered in the housing and management of farm animals (Hoy 1995). Since in the wild, mink (Mustela vison) are highly associated with wa- ter ways and get a large proportion of their food from these resources (Dunstone 1993), it may be argued that swimming has a high functional value in mink as an appetitive behaviour. In ad- dition, water for swimming could be an element in thermoregulatory behaviour. This has led to a mailto:cpbhansen@zi.ku.dk 150 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Hansen, C.P.B. & Jeppesen, L.L. Behavioural consequences of denied access in mink debate about swimming being a behavioural need in farm mink. If so, it follows that if minks at farms are not given access to water for swim- ming their welfare is affected. In order to investigate this question, our group has kept mink with access to water for swimming together with a control group since 1995. Previ- ously, we have looked at differences in reproduc- tion (Skovgaard et al 1997a) and behaviour (Sk- ovgaard et al 1997b) when unmanipulated. The aim of the present experiment was to investigate the behaviour of mink when denied access to re- sources usually present in their environment. This was done both by the comparison between denied access to water and denied access to an empty compartment. Both cases were compared with the simultaneous deprivation from a third resource, the nest box. Lack of nest boxes is known to lead to an increase in stress hormones (Hansen and Brandt 1989, Hansen and Damgaard 1991). Though this may not tell how long term depriva- tion can affect the animals, it may contribute to the understanding of how the animals value the different resources when under the acute stress of being denied access to part of the normally accessible area. As an indicator of motivation to obtain a resource, we used the amount of scratch- ing on barriers blocking entry to the resources. This parameter was chosen as the animals nor- mally would scratch to get access to a restricted area. During standard farm routines the animals are sometimes barred temporarily from some ar- eas of their units which prompts the animals to scratch on the barrier. On occasions their scratch- ing lead to them regaining access by themselves and if not the barrier will eventually be removed. Hence, the animals should connect scratching with regaining access. Material and methods The animals Sixty-two female and sixteen male farm mink were placed in four groups according to a 2x2 experimental design: two cage sizes, large (L) and small (S), and two water conditions, with water (W) and without water (D=dry). Housing units (Fig. 1) consisted of either three standard mink cages (each length 900 mm x width 300 mm x height 450 mm, 0.27 m2 and 0.12 m3) or three larger fox cages (each length 1200 mm x width 650 mm x height 750 mm, 0.78 m2 and 0.59 m3). The left cage included a nest box, the middle cage a basin covering the entire floor and the right cage was empty. Forty of the mink were housed in the large units, thirty-eight in the small ones. The connection between the left and the right cage was through either the basin in the middle cage or a wire mesh tunnel above the basin. In nineteen of the small and twenty of the large units the basin was filled with water and with a few exceptions, cleaned and refilled once a week. This left us with the following four group: WL (N=20), WS (N=19), DL (N=20) and DS (N=19). If an animal wanted to go through the middle cage with a water basin, it had to dive into the water. In each group the proportions of males to females were the same. At the time of the experiment (the summer of 1997) the mink were one or two years of age and had been born and raised in their present environment. Procedure Observations were carried out in September 1997. One hour before the beginning of daily observations the animals had their access to the nest box and both the middle and the right cages barred. The behavioural data were collected us- ing the scanning method (Simpson and Simpson 1977) with ten scans with an interval of 10 min between each scan. Half of the animals were scanned in the morning, the other half in the af- ternoon. The order was reversed every day. Each animal was observed ten times a day on nine consecutive days. At the end of each day the barriers were removed. Feeding took place in the left cage at midday between the two observa- tion periods of the day. The behavioural parameters collected were: 151 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Vol. 9 (2000): 149–155. Stereotypy as defined by Ödberg (1978), Inac- tive, Scratching on the barrier to the tunnel, Scratching on the barrier to the middle cage, Scratching on the barrier to the nest box or Oth- er Activities. All elements except Inactive were combined into the category Activity. The vari- ous stereotypies are described in Table 1. For some calculations the three types of scratching were combined into Scratching (all). Only fre- quencies were used and were collected using Psion Workabout™ and calculated on the SAS© ver. 6.0 package. Stereotypies were expressed both as frequencies of observations and as pro- portion of Activity. Due to the scan sampling procedure employed and since group data vio- lated assumptions of parametric statistical tests, distribution-free methods were applied through- out. By comparing combinations of groups the effect of the cage sizes (WS+DS vs. WL+DL) and the water conditions (WS+WL vs. DS+DL) on the behavioural parameters was tested. The combined effect of cage size and water condi- tions was tested by comparing the four groups directly. Results The barriers to the nest boxes received between two and five times as many scratches as did the barriers to the middle cages and the tunnels. It was not possible to detect any difference among the four experimental groups with regard to scratching on the barrier to the nest box, the middle cage or the tunnel (Table 2). Except for mink in the large units without water (DL, P=0.068), each group, on average, scratched sig- nificantly less on the barrier to the middle cage than on the barrier to the nest box. Scratching into the tunnel was also significantly lower than into the nest box, except for the group in the small units and with no water (DS) which did not show any significant difference in scratch- ing (P=0.076). The two non-significant results had the same direction as the others. Mink in large units did more total scratching on barriers than mink in small units . It is also worth noting that there was as much scratching into dry mid- dle cages as there was into water filled basins. Fig. 1. Layout of cage units. Table 1. Descriptions of the various stereotypes. Biting Stereotyped intensive biting in the wiremesh. Horizontal Stereotyped side to side movement of the anterior body with the posterior part still. Vertical Stereotyped up and down movement of the anterior body with the posterior part still. Nipple Stereotyped circular movement with the head around or nearby the drinking nipple. Pendling Stereotyped end-to-end of cage movement of the whole body. Bottom Like Pendling but with simultaneous snout-circling directed towards the cage floor. Mixed Stereotype Like Pendling but with vertical stereotyped movement at one or both ends of the cage. Horizontal circling Stereotyped circling on the cage floor. Vertical circling Stereotyped running floor-wall-ceiling-wall. Jumping Stereotyped up and down movement of the entire body. 900 / 1200 mm 152 A G R I C U L T U R A L A N D F O O D S C I E N C E I N F I N L A N D Hansen, C.P.B. & Jeppesen, L.L. Behavioural consequences of denied access in mink Also, in no group was there any difference be- tween scratching into the tunnel and into the middle cage. The level of Activity was higher in the small than in the large units. This holds for both the combined small groups and for the dry groups (DL vs. DS). Though not significant the results of the water groups (WL vs. WS) pointed in the same direction. The absolute and proportional level of stereotypy was influenced the same way. There was more stereotypy in the small units in the dry group (DS) and in the small groups com- bined; for the water group alone there was a non- significant tendency in the same direction (WS>WL). Both measures of stereotypies were also more frequent (P<0.01 and P<0.001 respec- tively, P-values not indicated in the table) in the small dry groups (DS) as compared to the small water group (WS) and in the combined dry group. The significant differences concerning stereotypies were mainly caused by a very high proportional level of Stereotypy (x=41.7%) in the group of mink in small units with a dry mid- dle cage (DS). This result was not caused by one or two extremely stereotyping animals. Only one animal in this group did not perform stereotyped behaviour compared to six in the group in small units with water in the middle cage. Discussion The present experiment can be seen as a kind of a preference test where the animals could choose to gain access to the three facilities: 1) the nest box, 2) the tunnel and the right cage and 3) the middle cage (+/- water) and the right cage. It can be argued that previous experience may affect the outcome of such tests (Duncan 1992) but because the animals had equal experience with the facilities, their previous experience should not have interfered with the results. If their amount of scratching was taken as a workload or cost to be paid for a reward, then the animals were prepared to pay much more for access to the nest box than for access to any of the other facilities including the water-filled basin. This might indicate that, in the present design, access to the nest box is a greater need than access to the other facilities. Therefore the result suggests that there are situations in which access to the nest box is more important for the welfare of the animals than the access to water for swimming or an empty compartment. Whether this is also the case in other and more general situations re- main to be seen. Some support of this comes from Cooper and Mason (1997) using consumer Table 2. Observations of 90 scannings over four groups (WL, WS, DL and DS) plus combined water conditions (Water and Dry) and combined cage sizes (large and Small). Probabilities refer to neighbouring columns. Tests are Mann-Whitney U- tests. Probability levels: Not significant: -, 0.01