The influence of olfactory stimulation on the behaviour of dogs housed in a rescue shelter

01 stycznia 2007

Lynne Graham, Deborah L. Wells, Peter G. Hepper
Canine Behaviour Centre, School of Psychology, Queen's University Belfast, Belfast, Northern Ireland BT7 1NN, UK
Received 13 January 2004; received in revised form 16 August 2004; accepted 16 August 2004 Available online 7 October 2004

Abstract
This study explored the influence of five types of olfactory stimulation (control, lavender, chamomile, rosemary and peppermint) on the behaviour of 55 dogs housed in a rescue shelter. The dogs were exposed to each type of olfactory stimulation, through the diffusion of essential oils, for 4 h a day for 5 days, with an intervening period of 2 days between conditions. The dogs' behaviour was recorded on days 1, 3 and 5, during each condition of olfactory stimulation. Certain aspects of the dogs' behaviour were influenced by the odours. Dogs spent more time resting and less time moving upon exposure to lavender and chamomile than any of the other olfactory stimuli. These odourants also encouraged less vocalisation than other types of aroma. The diffusion of rosemary and peppermint into the dogs' environment encouraged significantly more standing, moving and vocalising than other types of odour. It is suggested that the welfare of sheltered dogs may be enhanced through exposure to appropriate forms of olfactory stimulation. Lavender and chamomile appear particularly beneficial, resulting in activities suggestive of relaxation and behaviours that are considered desirable by potential adopters. These types of olfactory stimulation may also appeal to visitors, resulting in enhanced perceptions of the rescue shelter and an increased desire to adopt a dog from such an environment.

1. Introduction
The value of odours for psychological well-being is well documented in the human literature. Research suggests that both our moods (e.g., Lawless, 1991; Ludvigson and Rottman, 1989; Moss et al., 2003) and our behaviour (e.g., Baron, 1990; Baron and Thomley, 1994; Raudenbush et al., 2001) can be influenced by the odours to which we are exposed. Lavender, chamomile and sandalwood, for example, have been shown to reduce anxiety and encourage positive affect (e.g., Moss et al., 2003; Roberts andWilliams, 1992; Schwartz et al., 1986), whilst peppermint, jasmine and rosemary have been reported to improve alertness and enhance cognitive performance (e.g., Diego et al., 1998; Kovar et al., 1987; Warm and Dember, 1990).

Recognition of the benefits associated with certain odours for human well-being has prompted recent research into the value of olfactory stimulation as a means of enriching the environment of captive animals.The valueof olfactory enrichment has beens tudied in a variety of species, including, for instance, cats (Pearson,2002;Powell,1995;Schuett and Frase,2001; Wells and Egli, 2004),mice (Buchbauer et al., 1991, 1993;Umezu, 2000;Umezu et al., 2001) and pigs (Bradshawet al., 1998).Many of these studies report changes in the behaviour and/or physiology of animals exposed to a variety of aromas including herbs, spices and the excrement, or body odour, of potential prey.Whilst thefindings arising fromsuchwork are far from conclusive in terms of their implications for the animals' welfare, the changes in behaviour and physiology recorded in response to olfactory stimulation cannot be denied, highlighting the potential value for a form of enrichment that is frequently overlooked.

The domestic dog is well renowned for its olfactory acuity (for review, see Schoon, 1997); odour introductionmay thus hold some potential as a formof enrichment for captive canids. Recent years have witnessed an increasing concern for the welfare of dogs housed in rescue shelters and other types of confinement, e.g., laboratories and boarding kennels. Studies have explored the effects of cage size, social contacts, and the introduction of cage furniture, toys and music on the behaviour and welfare of kennelled dogs (for review, see Wells, 2004). To date, however, the effect of olfactory stimulation on the behaviour and welfare of kennelled dogs is completely unknown. Information regarding the effects of enriching the environment of sheltered dogs through the provision of olfactory stimulation would prove very useful, furthering our understanding of how to house such animals in ways that promote their welfare whilst confined.

The following study investigated the behaviour of 55 dogs housed in a rescue shelter in response to five types of olfactory stimulation, namely, lavender, chamomile, peppermint, rosemary and no odour (control). The influence of the length of time the dogs were exposed to each condition of olfactory stimulation on the animals' behaviour was also examined to establish whether or not the dogs habituated to the odours.

2. Method
2.1. Study site

Dogs Trust Ballymena Co. Antrim (formerly known as the National Canine Defence League Ballymena), was employed as the study site. Dogs were housed singly, or in pairs, L. Graham et al. / Applied Animal Behaviour Science 91 (2005) 143-153 144in three rows of line-block style kennels. The front of each kennel consisted of a wire-mesh door, concrete walls, floor and rear. Kennels faced opposite each other and overlooked a paved quad along which visitors and staff could walk.

Each dog's kennelwas dividedinto twosections, referred tohereafter as ‘front' and ‘back'. Fromthe front of their kennels (72 in. wide#94 in. long#96 in. high), the dogs could view conspecifics housed in opposite line blocks, and humans as they walked past the front of the animals' pens.Whenever theywere at the secluded back of their kennels (75 in.wide#62 in. long # 72 in. high), the dogs were hidden from the view of the public, staff and other dogs.

The dogs' enclosures were cleaned thoroughly everymorning and as needed throughout the course of the day. The animals were fed once a day in the afternoon.

2.2. Subjects
Twenty-nine neutered male, and 26 spayed female, single-housed dogs, all randomly chosen, were used as subjects. The majority of the dogs were cross-breeds, thus preventing any valid analysis of breed differences. All of the dogs were healthy, and between 6 months and 8 years of age (mean age = 3.3 years, #3.46). All dogs had been housed at this rehoming centre for between 2 and 4 months and had adapted to kennel life. The sample employed was representative of dogs admitted to this particular site.

2.3. Olfactory conditions
Five conditions of olfactory stimulation were developed, including a control, in which dogs were exposed to no odours other than those arising naturally from their environment (e.g., odours from disinfectants and conspecifics), and four experimental conditions, in which dogs were exposed to the ambient odours of essential oils including lavender (Lavandula angustifolia), chamomile (Anthennis nobilis), rosemary (Cymbopogon citrates) and peppermint (Mentha piperata). Lavender and chamomile were employed for their sedatary properties, with these odourants having been shown to have a stress- reducing effect in humans and animals (e.g., Bradshaw et al., 1998; Buchbauer et al., 1991; Ludvigson and Rottman, 1989; Yamada et al., 1996). Rosemary and peppermint, by contrast, were used for their stimulating properties, having been reported to improve alertness in both human and non-human species (e.g., Diego et al., 1998; Kovar et al., 1987; Raudenbush et al., 2001; Warm and Dember, 1990).

All of the essential oils were diffused into the dogs' environment using oil burners (Aroma Thyme, UK). One burner was placed at the front of each dog's kennel and another at the rear to ensure as even a distribution of odourant as possible to both ends of the animal's enclosure. All burners were placed safely out of the dogs' reach.

2.4. Procedure
Dogs were exposed to each of the four experimental conditions of olfactory stimulation for a 4 h period (12-4 p.m., the shelter's opening hours) for five consecutive days (Monday-Friday),with an interimperiod of 2 days between each of the conditions.All of the dogswere exposed to the same odours in the same order since the wire mesh door at the front of the animals' enclosures did not prevent scent transmission. The dogs were studied in the control condition first, followed by the lavender, peppermint, chamomile and rosemary conditions.

Table 1: Ethogram of behaviours employed in the study
Behaviour Definition
Position Dog is located at the front of the kennel, on view to the public
Standing Dog is supported upright with all four legs
Sitting Dog is supported by two extended front legs and two ?exed back legs
Moving Dog is walking, running, or trotting about the cage
Resting Dog is reclining in a ventral or lateral position, eyes open
Sleeping Dog is reclining in a ventral or lateral position, eyes closed
Stereotyping Dog is performing repetitive, functionless behaviour
Vocalise Dog is barking, whining or whimpering

The behaviour of each dog was recorded on days 1, 3 and 5 during both the control condition and each of the experimental conditions, in line with previous work of this nature (for review, see Wells, 2004). Observations of the animals' behaviour commenced 30 min following the diffusion of the odours into the dogs' pens. The experimenter (LG) approached the front of each subject's kennel and recorded the dog's behaviour as soon as she saw the animal. Each dog's behaviour was recorded every 10 min over the recording period using a scan-sampling technique (e.g., Martin and Bateson, 1986), providing 24 observations of each animal's behaviour per day. At every sample point, the behavioural state of each individual was recorded according to an ethogram devised from existing work in this area (Wells and Hepper, 1998, 2000;Wells et al., 2002a,b) [see Table 1]. All of those behaviours recorded are known to influence public perceptions of dog desirability and are believed to be useful indicators of canine welfare (Wells, 1996; Wells and Hepper, 1992).

2.5. Data analysis
The total number of times each dog was observed performing each behaviour was summed for each condition, providing an overall frequency count per animal per behaviour for each day of the study. For each behaviour (e.g., rest and stand) a repeated measures design ANOVA (e.g., Howell, 1992) was conducted on this data for the within subjects factors of odour condition (control:lavender:chamomile:peppermint:rosemary) and day of observation (day 1:day 3:day 5) to determine whether the dogs' behaviour was influenced by the various odours and/or the length of exposure to the scents.

The assumptions underlying parametric analysis (e.g., Howell, 1992) were sufficiently met in terms of population normality, sample independence, and homogeneity of variance (Mauchly Sphericity, and Kolmogorov-Smirnov, tests, n.s.).

3. Results
3.1. Standing

The analysis revealed a significant main effect of odour condition for the behaviour of standing (F(4216) = 3.15, P < 0.05). Dogs spent significantly (P < 0.05, Bonferroni test) more of their time standing during the peppermint and rosemary conditions than the control, lavender or chamomile conditions (see Table 2).

Table 2: The mean (±S.E.) number of times that dogs were observed performing each behaviour according to condition of olfactory stimulation
Behaviour Olfactory condition, mean (±S.E.)
Control Lavender Chamomile Rosemary Peppermint
Standing 3.98 (0.43) 3.62 (0.49) 3.61 (0.44) 4.85 (0.50) 5.21 (0.60)
Resting 14.73 (0.69) 17.96 (0.72) 15.53 (0.81) 11.99 (0.78) 11.95 (0.77)
Moving 4.73 (0.48) 1.73 (0.41) 2.54 (0.41) 6.07 (0.51) 7.35 (0.57)
Vocalising 2.22 (0.35) 0.45 (0.12) 1.04 (0.17) 1.95 (0.34) 2.90 (0.43)
Sitting 0.53 (0.11) 0.69 (0.30) 0.72 (0.19) 1.08 (0.26) 1.10 (0.23)
Position 9.82 (0.96) 8.84 (0.87) 10.20 (0.83) 9.60 (0.72) 9.52 (0.84)

There was a significant interaction between the day of observation and the condition of olfactory stimulation (F(8432) = 2.73, P < 0.05). Dogs spent significantly (P < 0.05 for all paired t-tests) less of their time standing on days 3 and 5 than day 1 during the rosemary condition. The amount of time that the dogs were recorded standing did not change significantly over the 3 days of observation for any of the other olfactory conditions (see Fig. 1).

 

3.2. Resting
There was a highly significant main effect of odour condition for the behaviour of resting (F(4216) = 18.82, P < 0.001). Pairwise comparisons showed that the dogs spent significantly (P < 0.05) more of their time resting during the lavender condition than any of the other conditions (see Table 2). The dogs also spent significantly (P < 0.05) more time resting during exposure to chamomile than rosemary or peppermint. By contrast, the animals spent significantly (P < 0.05, Bonferroni test) less of their time resting in the rosemary and peppermint conditions than any of the other conditions of olfactory stimulation.


Fig. 1. The mean (±S.E.) number of times that dogs were observed standing on days 1, 3 and 5 for each condition of olfactory stimulation.


Fig. 2. Themean (±S.E.) number of times that dogs were observed resting on days 1, 3 and 5 for each condition of olfactory stimulation.

The ANOVA revealed a significant interaction between day of observation and condition of olfactory stimulation (F(8432) = 5.89, P < 0.001). The dogs spent significantly less of their time resting on days 5 of exposure to rosemary and peppermint than on days 1 or 3 of exposure to these odourants (P < 0.05 for all paired t-tests). The amount of time that the dogs were recorded resting did not change significantly over the 3 days of observation for any of the other conditions (see Fig. 2).

3.3. Moving
The amount of time that the dogs were observed moving differed significantly between the various conditions of olfactory stimulation (F(4216) = 30.63, P < 0.001). Dogs spent significantly (P < 0.05, Bonferroni test) more time moving during exposure to peppermint and rosemary than all other odours (see Table 2). Dogs also spent significantly (P < 0.05, Bonferroni test) more time moving during the peppermint, than the rosemary, condition. By contrast, dogs spent significantly (P < 0.05, Bonferroni test) less of their time moving during exposure to lavender and chamomile than any of the other olfactory conditions.


Fig. 3. The mean (±S.E.) number of times that dogs were observed moving on days 1, 3 and 5 for each condition of olfactory stimulation.

The amount of time that the dogs were observed moving differed significantly between the various conditions of olfactory stimulation (F(4216) = 30.63, P < 0.001). Dogs spent significantly (P < 0.05, Bonferroni test) more time moving during exposure to peppermint and rosemary than all other odours (see Table 2). Dogs also spent significantly (P < 0.05, Bonferroni test) more time moving during the peppermint, than the rosemary, condition. By contrast, dogs spent significantly (P < 0.05, Bonferroni test) less of their time moving during exposure to lavender and chamomile than any of the other olfactory conditions.

3.4. Vocalising
There was a highly significant (F(4216) = 14.41, P < 0.001) main effect of odour condition on the dogs' vocalisation (see Table 2). Pairwise comparisons (Bonferroni test) indicated that the animals spent significantly (P < 0.05) less of their time vocalising during exposure to lavender than all other odours, and less time vocalising in the chamomile condition than all conditions with the exception of rosemary. The dogs, by contrast, spent significantly (P < 0.05) more of their time vocalising during exposure to peppermint than to either lavender or chamomile and more of their vocalising during exposure to rosemary than to lavender.

3.5. Sitting
The amount of time that the dogs were observed sitting did not differ significantly (F(4216) = 2.30, n.s.) between the various conditions of olfactory stimulation (see Table 2).

3.6. Position
The dogs' position in their kennels was not significantly affected by their olfactory environment (F(4216) = 0.82, n.s.).

3.7. Other behaviours
The dogs were never recorded sleeping or stereotyping and thus these behaviours were omitted from the statistical analyses.

4. Discussion
The findings from this study indicate that dogs housed in rescue shelters are significantly influenced by their olfactory environment.

Certain odours, in particular lavender and, to a slightly lesser degree, chamomile, resulted in the dogs behaving in a manner suggestive of increased relaxation. Both odours encouraged the dogs to spend less of their time moving and more of their time resting than the other experimental conditions of olfactory stimulation (and also the control, in the case of lavender). These odourants also resulted in a lower level of barking than all other conditions. Lavender and chamomile arewell renowned for their sedative properties.Many studies provide support for their stress-reducing effect in humans (e.g., Itai et al., 2000; Lorig and Schwartz, 1988; Millot et al., 2002; Motomura et al., 2001), and their tranquillising influence on animals (e.g., Bradshaw et al., 1998; Buchbauer et al., 1991, 1993; Kagawa et al., 2003; Yamada et al., 1996). Such odours may be of particular value to sheltered dogs. Rescue shelters are extremely stimulating environments. Dogs housed in kennels are exposed to a wide array of psychological stressors, including noise, confinement, unpredictability and loss of control (Hennessy et al., 1997; Tuber et al., 1999). Diffusing odourants with sedatary properties into the dogs' quarters may result in a slightly less stressful environment for the animals housed within.

Enhancing the olfactory environment of rescue shelters through the diffusion of odours that have a calming effect on the animals may also help to encourage more positive perceptions of dog behaviour and thereby increase rehoming success (see Wells and Hepper, 1992, 2000). Presenting odours that are known to ameliorate anxiety in humans (e.g., lavender, chamomile, sandalwood), may also reduce levels of stress and encourage visitors to spend more time touring the facility. This, in turn, may result in an increased amount of time looking at the animals housed there, and a subsequent increase in the number of dogs that are adopted (see Wells and Hepper, 2001). To date, research has only explored the impact of improving the visual environment of rescue shelters on potential visitors' perceptions of the dogs housed there (Wells, 1996; Wells and Hepper, 1992). Further research is required, however, to explore the effects of background odours on the adoption rate of sheltered animals.

Rosemary, and in particular, peppermint, encouraged the dogs to spend more of their time alert (i.e. standing, moving) than any of the other olfactory conditions. These scents also encouraged a greater amount of vocalisation. The findings from this study support previous research regarding these odourants. The essential oils of peppermint and rosemary have been found, for example, to promote both physical and mental stimulation in humans (Moss et al., 2003; Raudenbush et al., 2001; Warm et al., 1990, 1991) and to increase the activity level of captive lions, chimpanzees and mice (e.g., Kovar et al., 1987; Pearson, 2002; Powell, 1995; Umezu et al., 2001). That these odours had a stimulating effect on the dogs in this study, is thus perhaps not surprising. Odours with stimulating properties may serve some value for certain types of sheltered dogs (although not all, see later). Animals that have been housed in kennels for lengthy periods of time can develop behaviours symptomatic of learned helplessness, e.g., increased resting/sleeping (Wells et al., 2002a). The introduction of odours with stimulating properties may be advantageous for such animals, helping to promote mental stimulation and enhanced psychological well-being. L. Graham et al. / Applied Animal Behaviour Science 91 (2005) 143-153 150There is always the possibility, however, that animals exhibiting a depressive-like state, may go on to develop a more active type of aberrant behaviour (e.g., stereotypy) following exposure to stimulating odours. Further work is needed to explore this in more depth.

The dogs' behaviour changed significantly with length of exposure to some of the odourants, although not in a direction suggestive of habituation. Indeed, dogs actually became more active with increased exposure to those odourants with stimulating properties. Scents with a more sedative nature, by contrast, did not seem to alter the dogs' behaviour over time. This discrepancy is particularly interesting in light of the fact that all odours were diffused into the dogs' environment for exactly the same length of time; one might thus have expected a similar change in the animals' behaviour over time for all conditions, not just those with stimulating tendencies. It is encouraging to note that the dogs did not habituate to any of the odours, particularly those renowned for their stress-reducing properties, i.e. lavender, chamomile. Whether or not the animals would have eventually habituated to such odours with more prolonged exposure remains open to speculation and warrants investigation.

This study does admittedly suffer from the weakness that all dogs were exposed to the same odours at the same time due to the fact that the wire-meshed doors did not prevent scent transmission; order effects could thus not be controlled for. This raises the slight possibility that the results are due to some time-related factor rather than the olfactory environment. That said, no obvious differences in external stimulation across the various weeks of the study were noted by the experimenter, strengthening the likelihood that the odours, rather than some extraneous factor, was responsible for the change in the animals' behaviour. The inclusion of an extra control period at the end of the experimental conditions might have been worthwhile, enabling any gradual changes in the dogs' behaviour, arising from the experimental procedure or from adaptation to the shelter environment, to be established.

Overall, the findings from this study suggest that the behaviour of sheltered dogs is influenced by their olfactory environment and that certain types of olfactory stimulation may be beneficial for the animals' welfare. It is particularly important, from an animal welfare point of view, that an appropriate form of olfactory stimulation is employed in the shelter environment. Rescue shelters are extremely challenging environments. Adding odours that cause increased agitation or stress,may actually domore harmthan good. Thus, dogs that are showing hyperactivity or high levels of stereotypy should ideally be denied exposure to odours with a stimulating nature. Providing olfactory stimulation that has a calming influence on the dogs, however, may be advantageous, resulting in improved animal welfare, enhanced perceptions of dog desirability and an increase in the number of dogs that are re-homed.

Acknowledgements
The authors would like to thank Dogs Trust for allowing this research to be undertaken. The support of staff at Dogs Trust Ballymena Rehoming Centre is also gratefully acknowledged

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