Impact of environmental enrichment on animals

The interactions of environment and genotype are regarded as part of the environmental variance responsible for the variability in quantitative characteristics (GÄRTNER et al. 1979). Several studies prove the existence of this interaction such as effects on immunological status (BOHUS et al. 1993; STEFANSKI 2000;

MARASHI et al. 2003), the breeding performance (PRYOR & BRONSON 1981; TSAI et al. 2003), the activity in an Open Field (MORSE et al. 1993; DEVI et al. 1995) and changes regarding the performance of behavioral pattern (DAHLBORN et al. 1996).

In the studies of BOHUS et al. (1993) and STEFANSKI (2000) rats were confronted

ratios of IgG2a/IgG1 were significantly higher in mice from the spacious terrarium.

The absolute percentages of CD8 cells in mice from cages enriched with the box and the scaffolding were significantly lower than those in mice from non-structured cages.

The study of TSAI et al. (2003) compared the effects on the breeding performance in DBA/2 mice of three different housing conditions (individually ventilated cage (IVC), ventilated cabinet and open rack) in non-enriched and enriched cages. The enriched cages contained a nest box, a wood bar for climbing and nesting material. PRYOR &

BRONSON (1981) found out that at a change of the environmental factor temperature from 23°C to 3°C led to a decrease of the reproductive index of wild.

MORSE et al. (1993) compared the travel distance in an open field of single-housed female mice and group-housed females and found out that the single-housed individuals showed a significant higher activity. In contrast to that when being exposed to noise (with or without 3.5 MHz ultrasound) during the fetal development the group of Swiss mice that was confronted with ultrasound showed a decreased activity in the Open Field (DEVI et al. 1995). The study of DAHLBORN et al. (1996) revealed that BALB/c mice from enriched environments were more active, interact more with the enriching objects and had a lower food and water intake than mice of non-enriched cages. In the same study also three different enriching situations were compared and the group of animals provided with additional nesting material became heavier than the mice of the other groups. All these experiments show that environmental enrichment can alter experimental results and that the different enrichment situations influence the experimental outcome differently. Furthermore, an enriched environment may also lead to problems in groups of animals such as an increased fighting behavior in male mice (HAEMISCH & GÄRTNER 1994; TSAI 2002), which can lead to a reduced well-being. Other authors, however, claim that environmental enrichment leads to a more stable animals’ reaction in experimental

results (CHAMOVE 1989a,b; SCHARMANN 1991; ESKOLA et al. 1999). Despite this controversy it is generally accepted that a monotonous environment lacking stimuli as well as an insufficient stimulation during rearing and maturation hinder the development of animals in many respects. So learning deficiencies (DAVENPORT et al. 1976; JOSEPH & GALLAGHER 1980) and changes concerning the development of brain structures (CUMMINS 1977; RENNER & ROSENZWEIG 1987, BENEFIEL &

GREENOUGH 1998; WÜRBEL 2001) have been reported. Furthermore behavioral changes such as increased anxiety (ADER 1965; HOLSON 1986) occur. In addition to that abnormal behavior called stereotypy often occurs that may lead to massive changes in the animals. This again may influence the outcome of animal experiments resulting in an increased variance (WÜRBEL & STAUFFACHER 1995).

The aim of environmental enrichment is to improve the animals’ living conditions.

VAN DE WEERD et al. (1998) states that enriched environments improve the well-being of animals, which is shown by more behavioral expressions. Additionally, animals feeling well show less anxiety during behavioral testing (KLEIN et al. 1994).

In this study rats from enriched or non-enriches were confronted with cat urine and the enriched groups were less defensive. Furthermore, BOEHM et al. (1996) state that mice from enriched housing conditions have improved learning abilities. This is demonstrated by their study in which enriched cage mice showed increased activity, greater speed, and enhanced learning scores across a variety of tests. Additionally, prior test experience itself had significant positive effects on Hebb-Williams maze learning. Environmental enrichment also has beneficial effects on neurological parameters such as increased dendritic spine density (TURNER et al. 2003).

In conclusion, in order to meet the animals’ requirements and improve the animals’

well-being as well as meeting the provisions of the ETS No.123 (COUNCIL OF EUROPE 2004) an appropriate environmental enrichment has to be established for each species, gender and strain.

commentaries to the German Animal Welfare Act LORZ (1999) gives a generally accepted definition of animal well-being. According to him, well-being is a state in which the animals experiences both physical and mental harmony within itself and with the environment. To achieve physical health and normal behavior, the constant signs of well-being, an undisturbed and species-specific course of life meeting the behavioral needs is required.

VAN PUTTEN (1982) and MEYER (1984) describe well-being to be a physical and psychological state characterized by the animal’s opportunity to satisfy species-specific and individual needs. This state will be maintained if the normal body function lasts for long period of time. In conclusion well-being consists of two components: the state of health, which is an objective criteria for well-being, and the emotional state, which is a subjective criteria. Hence, the absence of pain and suffering is a pre-requisite for well being, but it is not sufficient to ensure it as well as healthiness is not to be equated with well-being. However, it is generally accepted that any interferences with the health will always lead to a decreased well-being (LORZ 1999). Unfortunately, in animals there is a lack of scientific methods to measure their feelings and emotions directly (TSCHANZ 1985; MILITZER 1986).

Therefore, it is common to define an animal’s individual state of well-being by detecting the absence of specific -again subjective- states (DAWKINS 1980). SMIDT et al. (1980) also believe that well-being is a reflection of the animal’s physical and psychological integrity that can only be concluded from certain symptoms (DAWKINS 1993; FRASER et al. 1997). As a result well-being is implied if the animal does not show any signs of pain, suffering or harm including abnormal behavior of a physiological healthy animal (DAWKINS 1980). As well-being comprises more than the absence of pain, suffering or harm it is not sufficient to only describe harmful effects on the well-being. It is necessary to define further (positive) requirements of

well-being (TEUTSCH 1987). Many authors agree that animals, showing a large variety of their behavioral repertoire and being able to reproduce, feel well (BROOM

& JOHNSON 1993; TSCHANZ 1997). The definition of animal well-being given by BROOM (1996, 1998) meets both the requirements of physical and psychological health because he suggests that an animal experiences welfare if it is able to cope with its environment. Play behavior is considered to be an essential behavioral pattern and is also called ‘König der positiven Parameter’ [king of positive parameters] (GRAUVOGEL 1982,1983). Play behavior is only performed in situations of relaxed atmosphere and consequently the animal’s needs are satisfied (SMIDT et al. 1980; GRAUVOGEL 1982, 1983). JUHR (1990) also considers play behavior -especially in juvenile animals- to be an unmistakable sign of well-being because specific needs such as hunger, thirst or pain are then satisfied. Another important characteristic of well-being is the environment and the possibility to have some control over it, respectively. TSCHANZ (1986) developed the concept of

“Bedarfsdeckung und Schadensvermeidung” [ability to meet one’s needs and to avoid harm] to scientifically determine the states of health and psyche. He points out that the animal’s senses enable it to detect necessary resources in its environment and to use these resources by performing specific behavioral pattern. Provided that the environment contains animal-specific conditions, and that the genetic background or the ability to adapt allows the animal to show appropriate behavior, it has the ability to meet its needs and to avoid harm. Only if the animal’s needs, its behavioral repertoire, and its ability to adapt are well-known housing conditions can be optimized.

2.5 Suffering

In human medicine terminology suffering is used to describe a chronic disease associated with reluctance. In contrast to that LORZ (1999) states that the term

‘suffering’ comprises every adverse effect on well-being not included into the definition of pain which is beyond discomfort and lasts for a relevant period of time.

Preliminarily, it concerns impacts on and interferences with the well-being that are in

and administrative provisions of the Member States regarding the protection of animals used for experimental and other scientific purposes (86/609/EEC) (COUNCIL OF THE EUROPEAN COMMUNITIES 1986). Here man’s ethical obligation for the protection of animals is stressed by pointing out that the animals’

ability to suffer and to memorize has to be considered properly. Suffering can be a consequence of pain and stress if an animal is exposed to long-term strain overtaxing its ability for adaptation (HACKBARTH & LÜCKERT 2002). In this context SALOMON et al. (2001) describe that a man-made environment lacking stimuli may restrain animal behavior so that situations of insecurity and loss of control may occur which can be assigned to the process of suffering. Similar to pain suffering is a subjective and therefore not completely comprehensible state and it is difficult to confirm by means of scientific measurements (WOLFF 1993). Thus it is inevitable to observe the animals while having biological and ethological knowledge of the species and its needs. An animal’s indisposition can develop into a straining situation depending on the intensity of this state and how long is lasts. In this case indisposition describes a disparity between the current environmental circumstances and the animal’s desired intrinsic condition. The animal will attempt to overcome this discrepancy by performing certain behavioral pattern. If those trials are unsuccessful the state of suffering begins containing obvious behavioral disorders and anomalies such as stereotypies. Consequently suffering in animals can be recognized if observed behavior differs from the normal behavior and if the animals do not respond to external stimuli as they used to.