INTRODUCTION

Laboratory animals such as rabbits are bred and housed for experimental use. The living conditions, housing, and husbandry are often more obstructive and more stressful for the animals than the experimental procedure itself. Therefore, the potential negative effects of an experiment on a laboratory animal's well-being are not restricted to the experiment itself but instead cover the whole life span of the animal.

Discussions of welfare requirements and their practical implementation could be improved substantially if decision makers would bear in mind that the desire to protect animals in captivity is based on ethical considerations of humans. However, in contrast to this perspective, the true well-being of captive animals should be based on a biological understanding that relates to the specific needs of the respective species and strains.

In 1986, the current housing standards for laboratory rabbits were established in Article 5 of the Council of Europe's Convention for the Protection of Vertebrate Animals Used for Experimental and Other Scientific Purposes (CoE 1986): “Any animal used or intended for use in a procedure shall be provided with accommodation, an environment, at least a minimum degree of freedom of movement, food, water and care, appropriate to its health and well-being. Any restriction on the extent to which an animal can satisfy its physiological and ethological needs shall be limited as far as practicable. In the implementation of this provision, regard should be paid to the guidelines for accommodation and care of animals set out in Appendix A to this Convention….” Cages and pens “should be designed for the well-being of the species” and “should permit the satisfaction of certain ethological needs (for example the need to climb, hide or shelter temporarily)…” (CoE 1986, Appendix A, paragraph 3.6.3).

However, on the species-specific level, the guidelines are restricted to recommendations on minimum cage dimensions and stocking densities. Regulations set up by a political body do not define an optimum but instead set limits and minimum standards. All concepts of animal protection are composed of conventions and assessments that are inevitably linked to those individuals who prepare and make the decisions. Working out minimum requirements with respect to animal welfare (ethical) and to the supposed well-being of laboratory animals (biological) is, last but not least, a political (mostly economical) question. Nevertheless, the decision-making process must be based first and overall on sound arguments concerning the biology of species and strains in question.

The environment of a rabbit kept in captivity—as a pet, for fattening, or in the laboratory—has a considerable impact on its well-being and functioning. Important environmental factors include not only climate (e.g., light cycle, temperature, relative humidity, ammonia concentration, and ventilation) but also hygiene, food and water supply, housing, and the presence of conspecifics. In this presentation, we focus on the housing environment.

ESTABLISHED SPACE REQUIREMENTS

The minimum space requirements of the European Convention (CoE 1986) are based on a mathematical calculation model with arbitrarily set constant factors, slope, and starting point. The slopes represent weight-bands and allow the space requirements for a given number of rabbits to be calculated. The heavier the rabbits, the fewer square centimers of space are required per weight unit. The calculation model refers only to body weight and does not make a distinction between strains, sex, and age. As a result, this model does not adequately reflect the fact that young, growing animals need much more space in relation to their body weight than adults.

The minimum space requirements of the European Convention ETS 123, Appendix A, 1986, apply to a medium-sized (< 4 kg) rabbit such as the New Zealand White rabbit: 2500 cm² with a height of 35 cm. However, in the Sixth Edition of the Guide for the Care and Use of Laboratory Animals (the Guide) (NRC 1985), the requirement applies to a rabbit of 2700 cm² with a height of 35 cm.

When we consider the current standard housing of laboratory rabbits from a human point of view, single-housed animals are easy to control and handle. Animal staff can easily handle a cage size of approximately 2500 cm² with a height of 35 cm and can easily disinfect the metal and plastic walls. The slatted or perforated floors allow automatic cleaning, and the pelleted food and water bottles can be controlled. All of these factors are consistent with Good Laboratory Practice.

In contrast, from the rabbit's perspective, the current housing practices provide the following characteristics: limited freedom of movement, a barren cage environment with restricted challenges and possibilities for occupation, no social partners, and an artificial open nest-box. All of these characteristics afford the rabbit hardly any possibility of performing species-specific behavior.

A series of studies have shown that in cages that comply with the minimum dimensions required in Appendix A of the European Convention (CoE 1986), the welfare of laboratory rabbits is impaired (Stauffacher 2000). The consequences of limited freedom of movement are changes in locomotor patterns and sequences (e.g., inability to hop), which result in skeletal damage in, for example, the femur proximalis and the vertebral column (Bigler 1995; Drescher 1993). The barren cage environment with a severe lack of stimulation leads to behavioral disorders such as wiregnawing and excessive wall-pawing, as well as to panic reactions and signs of “boredom” (Lidfors 1997). During breeding, an open nest-box and poor quality and quantity of nesting material do not permit the natural behavior of the doe (e.g., closing up the nest entrance when triggered by odor cues of the litter). In addition, these conditions do not allow the doe any chance to withdraw from the litter, which can result in behavioral disorders in the mother and in significant rearing losses (Stauffacher 2000).

In 1997, the Multilateral Consultation of the Council of Europe adopted a resolution on the accommodation and care of laboratory animals, which specified that “young and female rabbits should be housed in socially harmonious groups…” and that “pens, as well as cages, should include enrichment material e.g. roughage, sticks, an area for withdrawal and nesting material.” As a consequence of that resolution, an international expert group was set up in 1998 to devise science-based proposals for a revision of Appendix A.

RABBIT BEHAVIOR AND NEED FOR SPACE

Rabbits do not use space per se; they use resources and structures within an area for specific behaviors. Appropriate structuring of the cage/ pen environment may be more beneficial than provision of a larger floor area; however, a minimum floor area is needed to provide a structured space (e.g., blinds, shelters, and platforms) that includes withdrawal areas and vantage points.

Rabbits tend to be highly motivated, to make use of enrichment based on food items, and to satisfy their need for roughage (hay, straw) and gnawing (soft wood chew sticks). With respect to the social environment of rabbits, the domestic rabbit with its wild ancestor the European wild rabbit (Oryctolagus cuniculi L.) is a highly social animal that lives in the wild in stable groups of one male, three to five females, and their offspring in a home territory or “warren.” They establish a linear rank order (males and females), and subadult males must leave the warren.

A social partner always creates new and unpredictable situations to which a rabbit must react. Such situations lead to an increase of alertness and exploratory behavior, and provide diversion, occupation, and probably also some feelings of “security.” References to these situations appear in the following documents: (1) The Council of Europe Multilateral Consultation on the Revision of the Convention for the Protection of Animals Used for Scientific or Other Purposes, ETS 123, Part II, Appendix A, 1997: “Young and female rabbits should be housed in socially harmonious groups unless the experimental procedure or veterinary reasons make this impossible.” (2) The Seventh Edition of the Guide (NRC 1996): “Animals should be housed with a goal of maximizing species-specific behaviors and minimizing stress-induced behaviors. For social species, this normally requires housing in compatible pairs or groups.”

The crucial question, however, is how to assess minimum recommendations. To determine the minimum recommendations for sizes of primary enclosures (cages, pens) for laboratory rabbits, it is necessary to consider both the quantity and the quality of space. The crucial point is the interaction between the space—the structure of the cage, the rabbits, and the type and quantity of enrichment provided. These variables must be based on experimental results and scientific papers, good/best practice, and experimental constraints. Although good scientific arguments may exist regarding why limits should be set in particular cases, the exact numeric values for minimum cage sizes and heights as well as for maximum stocking densities can never be scientifically evaluated and “proved.”

RECOMMENDATIONS AND ANTICIPATED REVISIONS

In the proposal for the revision of Appendix A of the European Convention ETS 123, the Expert Group on Rodents and Rabbits recommends that medium-sized (< 4 kg) rabbits such as New Zealand White rabbits should be housed in cages with a floor area of 4200 cm² and a height of 45 cm, including a raised area of approximately 55 × 30 cm where one rabbit or two compatible rabbits can be housed. Without a raised area, floor space should be 5600 cm² for one rabbit and 6700 cm² for two rabbits. According to Swiss law, one rabbit or two compatible rabbits can be housed in a cage with a floor that measures 4200 cm² + 1800 cm² with a height of 60 cm (SOAP 1991).

In the process of refinement of housing standards, the following points should be taken into account:

1. Biological facts and scientific evidence (related to the animals);
2. Experimental tasks and constraints (related to the research goals);
3. Practical experience (related to the debating subjects);
4. Ethical principles (related to animal protection); and
5. Assessment of economical and political reasonableness (related to human societies).

REFERENCES

1. Bigler L. Bern: Bericht z.Hd. Bundesamt für Veterinärwesen; 1995. Zusammenfassung der Ergebnisse radiologischer Untersuchungen an Zuchtzibben-Wirbelsäulen und Mastkaninchen-Femurknochen in der Schweiz von 1984-1995 [in German]
2. CoE [Council of Europe] European Convention for the Protection of Vertebrate Animals Used for Experimental and Other Scientific Purposes (ETS 123). Strasbourg: Council of Europe; 1986.
3. Drescher B. Zusammenfassende Betrachtung über den Einfluss unterschiedlicher Haltungsverfahren auf die Fitness von Versuchs- und Fleischkaninchen [in German] Tierärztl Umschau. 1993;48:72–78.
4. Lidfors L. Behavioural effects of environmental enrichment for individually caged rabbits. Appl Anim Behav Sci. 1997;52:157–169.
5. NRC [National Research Council] Guide for the Care and Use of Laboratory Animals. 6th Ed. Washington, DC: National Academy Press; 1985.
6. NRC [National Research Council] Guide for the Care and Use of Laboratory Animals. 7th Ed. Washington, DC: National Academy Press; 1996.
7. SOAP [Swiss Ordinance on Animal Protection] Bern: Eidgenössische Daten-und Materialzentrale; 1991. Schweiz. Tierschutzverprdnung vom 27. Mai 1081, Änderung vom 23. Oktober 1991.
8. Stauffacher M. Refinement in rabbit housing and husbandry. In: Balls M, Van Zeller AM, Halder ME, editors. Progress in the Reduction, Refinement and Replacement of Animal Experimentation. Amsterdam: Elsevier Science B.V. Publ; 2000. pp. 1269–1277.