Though European rabbits are a social species, socially housing them can be challenging. Therefore, there must be a thorough understanding of behaviors and social structures of pair-housed laboratory rabbits. Here we present a protocol to identify pairing methods, species-typical hierarchy establishment behaviors and behaviors that warrant appropriate intervention.
New Zealand White (NZW) laboratory rabbits (Oryctolagus cuniculus), as well as their ancestors the European Rabbit, are a social species that exhibit numerous benefits to being housed accordingly. Although these rabbits are innately gregarious, certain behaviors can still arise when kept in captivity, which if left unchecked, can confound research results or lead to wounding, which in extreme cases can be severe. To prevent these issues, there must be a well-structured plan for the monitoring and maintenance of paired laboratory rabbits. The purpose of this protocol is to present effective procedures for establishing newly paired NZW rabbits as well as methods for successful maintenance. Multiple methods have been tested for the creation of newly paired female rabbits from the vendor, but the most efficacious technique emphasizes capitalizing on the stress bonding from transport, urine marking, pairing in a neutral cage with no forced sharing of resources and a system of monitoring and intervention. To determine the best method of housing paired rabbits in a standard caging environment, data were collected to generate a behavioral ethogram. Behaviors were then quantified as positive, neutral or negative and were tracked across the lifespan of the pair to determine which behaviors indicated pair success or failure. With the newfound knowledge of socially housed laboratory NZW rabbit behavior, enrichment intervention was applied to alleviate aggression and prevent wounding, thus resulting in a higher percentage of successful pairs. Through several years of trialing different pairing methods, the development of the ethogram and the resulting enrichment interventions, understanding of the highly complex social constructs that dominate pair housed rabbit behavior has dramatically increased and allowed for the provision of more species-specific care and increased standards of welfare.
The regulations governing laboratory animal care provide well-defined recommendations regarding rabbit social housing. Two of the three primary standards used by AAALAC International to evaluate animal care and use programs describe guidelines for species-appropriate husbandry and housing. The first of these guidance resources, the 8th edition of the Guide for the Care and Use of Laboratory Animals1 (Guide) states that social species such as rabbits should only be singly housed as an exception and single housing should not be the housing standard. The second, the European Convention for the Protection of Vertebrate Animals Used for Experimental and Other Scientific Purposes2, states that rabbits are an inherently social species that should be housed in accordant social situations with the exception of qualifying veterinary or research related reasons. The Office of Laboratory Animal Welfare (OLAW) also mandates that single housing is only appropriate when there is scientific justification that has been evaluated and approved of by the Institutional Animal Care and Use Committee (IACUC), the animals are incompatible or the veterinary staff has a health or welfare concern3.
In addition to meeting regulatory compliance, peer-reviewed literature provides many examples of the physical and psychological benefits of pair housing NZW rabbits. In order to provide the highest possible standards of animal welfare, species-appropriate housing must be provided while meeting the specific goals of the researcher. Socially housed NZW rabbits engage in more active behaviors4, display amplified fitness and show diminished levels of gastrointestinal stasis due to increased locomotor behaviors5. Physical activity is particularly important for laboratory rabbits as they are prone to osteoporosis4 when housed in a cage environment. In addition to the physical benefits of social housing, there is a myriad of psychological benefits. Pair-housed NZW rabbits display increased species-specific activities6, receive enrichment benefits from social stimulation4, show increased rates of self-soothing activities7 as well as affiliative behaviors such as allogrooming8 and exhibit an increased ability to manage anxiety from novel stimuli, i.e. stress buffering5. Additionally, in comparison to socially isolated NZW rabbits, socially housed NZW rabbits did not differ in immune function9 or antibody production10, however, singly housed rabbits did have higher heart rates11 and increased white blood cell counts10 when compared to socially housed rabbits.
Just as the benefits of social housing are well documented in the literature, so are the detriments of social isolation. Single housing of a social species can lead to physiological indicators of stress12. Singly housed NZW rabbits spend increased amounts of time being inactive and performing abnormal behaviors4 and stereotypic behaviors indicative of frustration13,14,15. Common stereotypes include: chewing on metal such as cage bars or feeder/waterer, excessive auto-grooming, licking of the cage and self-inflicted negative behavior16. If they must be housed singly, additional attention should be paid to counter-balance the stress from social isolation. The Guide recommends providing additional housing space, only housing singly for the minimum amount of time possible, allowing for occasional time in a larger housing situation such as a floor pen and providing additional and varied enrichment opportunities including interaction with other rabbits when possible1. AAALAC International additionally recommends providing protected access such that animals can have visual, auditory and olfactory contact with other animals17.
Given the choice, rabbits prefer to be with other rabbits. Preference testing demonstrated that female NZW rabbits worked almost as hard for limited social contact as they did for food18. Multiple other studies have shown that paired rabbits, when given the choice, were observed in physical contact with each other 4,8,19,20. These studies highlight the significant value rabbits place on socialization with conspecifics. Interestingly, these results do not apply to only female rabbits. When provided with a modified cage divider which was half opaque, half clear with small holes drilled into the clear portion to allow for enhanced but protected social access, male NZW rabbits spent more time in the quarter of the cage that provided the most access to a neighboring male than males in cages without the modified dividers. The male NZW rabbits with protected social access were significantly more active, spending more time in activity and rest behaviors and less on maintenance behaviors such as grooming which is associated with boredom and social deprivation. Males with a modified divider were also less fearful of unfamiliar staff as demonstrated by a reduced latency to approach an unfamiliar hand than males with a standard divider; possibly due to the social buffering effects of interaction with a partner21. Additionally, the circadian patterns of activity and rest of the male rabbits with modified dividers became synchronized in a crepuscular pattern, similar to wild rabbits, whereas socially isolated rabbits varied significantly from one another in their patterns of activity and rest21. Literature suggests that male rabbits are not ideal candidates for social housing due to aggression post sexual maturity14,22,23,24. In wild populations, females are more gregarious than males6 and multiple females often share a living space while males tend to maintain a larger distance between other males which can lead to increased aggression when placing males in the limited space of a laboratory cage15,25. Some studies have attempted to socially house males in a larger pen setting with mixed results14,22,26,27. One study attempted pairing males in a cage setting which resulted in all three pairs being separated for aggression14. The following protocol is the first to the authors' knowledge that allows for housing males with sibling males successfully in a cage setting into adulthood. There is no pairing of unrelated males or adult males due to the possibility of aggression and no male/female pairings due to the research uses of the colony.
The first step towards rabbit social housing is the establishment of new pairs. This article describes the methods that allowed for the greatest success within this institution of establishing new female pairs and the ethogram used for structured monitoring. The protocol utilizes methods such as urine marking6,28, stress bonding, providing neutral territory and assuring no forced resource sharing. In wild rabbit colonies, the dominant buck urinates on the rabbits of his breeding group (including kits, juveniles and does) thereby scent marking the rabbits that belong in his social group29. This idea has been translated to the laboratory setting by applying freshly collected urine from a male rabbit to the forehead of newly paired females. This imbues the females with a shared scent to indicate to them that they are within the same breeding group and they do not need to compete aggressively. An investigation of using urine marking in creating new female rabbit pairs found that unmarked pairs were more aggressive and exhibited less affiliative behaviors than pairs marked with buck urine6. Stress bonding has also been shown to be an effective method of pairing in the companion rabbit community by creating a mildly stressful situation that both rabbits are mutually exposed to in order to encourage bonding30. This is typically achieved by a car ride or a walk in a carrier. A theory is that the rabbits will carry over the feelings of security that they received from having a partner during this stressful time into their future bonding experiences and they, therefore, will be more likely to form a successful pair31. Pairing new arrival rabbits that have gone through the stress of transport from the vendor creates a natural stress bonding experience that can be capitalized on to assist with the pairing. Once pairs are established, an effective monitoring program must be implemented to track pair behavior over time in order to intervene when necessary. This article highlights the behavioral ethogram that was developed to enable a complete understanding of rabbit social behavior and methods for pair maintenance. Pair maintenance is often a point of difficulty in facilities due to a lack of comprehensive literature describing standard rabbit social interactions and what they may indicate. Rabbit pairs are often separated for interactions that appear to be fighting behavior but are actually normal social interactions that can be monitored and assuaged with proper intervention. This article looks to alleviate this by providing a broad list of behaviors to track and what they may be indicative of. Additionally, environmental enrichment intervention is utilized to aid in the prevention of pair failure. Adequate environmental enrichment may decrease fearful behaviors and allow for better coping with stressors1, reduce abnormal behaviors24,32, provide opportunities for essential physiological requirements33 and overall increase welfare34. The results of previous investigation at this institution showed that increasing environmental enrichment facilitates greater success in pair housing by decreasing the aggressive behaviors that arise around the age of sexual maturity (12-17 weeks)35. This method has a two-fold benefit; the enrichment creates a distraction to prevent fighting, as well as, allowing for positive interactions through species-typical behaviors.
This protocol followed the standards of care developed and utilized by the Unit for Laboratory Animal Medicine (ULAM) of the University of Michigan (U of M), which receives approval and oversight of all animal care procedures and methods by the IACUC. The IACUC is in full compliance with the eighth edition of the Guide. All rabbits were housed in cages that were a minimum of .46 m2 per cage which exceeds Guide minimum requirements.
1. Methods for the Creation of Female Pairs from Newly Arrived Rabbits that were not Pre-paired by the Vendor.
2. Methods for the Creation of Other Types of Pairs including Female Sibling Pairs at Weaning, Female Non-sibling Pairs within One Week of Age at Weaning, Female Weanlings with their Mother, Male Siblings at Weaning or Adults that were Pre-paired from the Vendor.
3. Observe for Positive/Affiliative, Neutral and Negative Behaviors.
4. Methods for Pair Maintenance with Environmental Enrichment Intervention.
Over a 12-month period, 172 NZW laboratory rabbit pairs (62% female, 38% male) were maintained following the above protocol. Of these pairs, only 20% of male pairs and 1% of female pairs had to be separated for fighting as shown in Figure 5. The pairs that were separated for fighting behaviors were separated at an average of 18.5 weeks old. The majority of total pairs of both sexes (63%) were separated for research purposes that were not related to pairing, with 29% of pairs still together and only 8% of total pairs having to be separated for aggression.
Of these 172 pairs, stable pairings were able to be maintained well into adulthood with the oldest male pair being 75 weeks old and the oldest female pair being 92 weeks old at the time of separation. Both of these pairs were separated for research purposes and had displayed no wounding and ample displays of affiliative behaviors during their time together. Unrelated females paired on arrival accounted for 21% of the female pairs with the remaining female pairs and all males being weaned together from an in-house transgenic breeding colony.
In total, only 14 of the 172 pairs were separated for aggressive behavior. Of these 14, only two pairs required veterinary treatment beyond monitoring (one required analgesia and one suture). Furthermore, of the 172 pairs in the last year, only two rabbits have had wounding that could not be alleviated with standard therapies or had a significant negative impact on their intended research use.
Figure 1: Rabbit Social Introduction Log. This log allows for detailed tracking of behaviors commonly seen during social introductions. The log is modified from the Royal Society for the Prevention of Cruelty to Animals (RSPCA) Ethogram37. Please click here to view a larger version of this figure.
Figure 2: Rabbit Social Introduction Log Additional Monitoring Log. This log allows for detailed tracking of behaviors observed post-pairing. The day of pairing requires two additional 10 min checks while the subsequent three days only require one additional 10 min check. Please click here to view a larger version of this figure.
Figure 3: Rabbit Social Housed Interaction and Enrichment Log. This log allows for detailed tracking of behaviors observed and enrichment intervention provided throughout the course of the pair's life. This document provides a detailed history of behaviors observed and the outcome of the intervention provided. Please click here to view a larger version of this figure.
Figure 4: Categories of Enrichment. This chart describes the different categories of enrichment that are provided to rabbits on a rotating schedule. Please click here to view a larger version of this figure.
Figure 5: Pair Outcomes by Sex. This figure shows that the majority of males and females were separated for research purposes with the second highest majority of rabbits still being paired. The smallest group of pairs that were separated was as a result of fighting. Please click here to view a larger version of this figure.
One of the most difficult challenges facing a rabbit social housing program is the differentiation between species typical aggressive or communication behaviors and problematic fighting behaviors. An in-depth and extensive knowledge of normal rabbit social behavior is required of all husbandry and veterinary staff monitoring the pairing process since many behaviors that appear to be a fight behavior are actually necessary hierarchy establishment behaviors that typically do not result in injury. For example, chasing and fleeing are common, daily behaviors within stable hierarchies that are used to reinforce rank6,29, but they may be seen as dangerous fight behaviors requiring separation to an untrained eye. Laboratory rabbits spend a significant percentage of their time engaging in aggressive behaviors that contribute to the continued maintenance of the pair hierarchy38 and wild dominant rabbits require submissive behaviors (e.g. fleeing) from subordinates as frequently as daily15. If an observer is unaware of this fact, it could lead to the separation of pairs that are behaving in a species-appropriate manner and do not have a concern that would warrant separation. Due to the intensity of these species-typical behaviors, it can be difficult to determine when to intervene and when to let a pair sort out issues on their own. This is especially important while creating new pairs that are ascertaining their dominance hierarchy for the first time. Too much human intervention can lead to the pair being unable to clearly establish a dominance hierarchy which can lead to pair breakdown. It is vital to have dedicated, educated technicians to monitor the pairs daily to know when behaviors are progressing past the point of normal dominance behaviors. Pairs should always be allowed to express species-typical behaviors when possible33.
Training is a vital step in the establishment of a successful rabbit social housing program. It is necessary to train and work closely with husbandry staff, veterinary staff and laboratory staff during every step of the pairing process to instruct them on what constitutes a separation worthy behavior and what is acceptable species-typical behavior. Laboratory personnel should be aware of how to contact the veterinary staff to report aggressive behaviors instead of routinely separating rabbit pairs. Proper training will eliminate the unnecessary separation of pairs that could have been kept together with increased enrichment and monitoring.
The failure rate of male pairs was likely higher than that of the females due to difficulty establishing a successful dominance hierarchy within a limited space cage setting. Dominant males require frequent submission activities from the subordinate rabbit15 and if these are not done the pair might not be able to establish an effective hierarchy, thus resulting in pair failure. Even if the subordinate rabbit is displaying the appropriate submission behaviors, the space constraint of a cage might not allow for adequate fleeing from the dominant6,39. This is one of the limitations to pairing males within a cage setting.
Another limitation of this method is that as of the time of publication, alternative scents have not been tested against buck urine for a control. It is possible that a scent that is more readily obtained by facilities that do not have an abundance of male rabbit urine will create the same effect. Previous work done into this concept showed that buck urine was more effective at limiting aggression than doe urine, so it is probable that the odor being from a male rabbit is more significant than it being a novel odor6, but this has not been tested within this institution. An additional limitation is that the protocol for pairing is only applicable to female new arrivals from a commercial breeder, females weaned with a female sibling or mother, or males weaned with a male sibling at this time. Optimization procedures are currently underway to investigate the most efficacious methods of pairing unrelated females already housed in the vivarium within a standard caging system, but further examination is still necessary before those methods can be confidently recommended. This method also has the restriction of only being applicable to sibling males that have been weaned together and not newly created male pairs. Published reports of creating new paired males in cages have been unsuccessful14 due to their high levels of aggression towards conspecific males. The maintenance and intervention sections of this protocol however, are applicable to females as well as males (paired at weaning) and as the results showed, can be extremely effective at housing paired males well past sexual maturity and into adulthood. This protocol has also only been tested with NZW rabbits. Additional investigation into other breeds of rabbits is necessary before this protocol can be applied to laboratory rabbit breeds other than NZW. The presented protocol has been tested in Dutch Belted rabbits successfully but not with significant enough numbers that the authors can confidently recommend this method for other breeds. Finally, the recordings were taken at random times during the standard workday. Therefore, behaviors that may be present only at night were not observed. These behaviors could be beneficial in understanding rabbit behavior since they are a crepuscular species and may display more active behaviors at dawn and dusk40.
Results show that adhering to the described protocol for social introductions, pair maintenance, and environmental enrichment intervention can lead to a successful NZW rabbit pair housed colony in standard caging with reduced negative interactions that maintain compliance and animal welfare standards. By understanding the behaviors typical to NZW rabbit social interaction and what they indicate, a much more rigorous and effective process was able to be developed which allowed for improvements in the rabbits' quality of life by creating stable pairs and maintaining the pair-housed experience for as long as experimentally possible.
The authors have nothing to disclose.
The authors would like to thank the multiple laboratories at the U of M that utilize rabbit models for the generous use of their colonies, in particular, the laboratory of Dr. Eugene Chen and the Center for Advanced Models for Translational Sciences and Therapeutics (CAMTraST) team. Thanks also to the U of M ULAM husbandry team, Jenny Jones for enrichment coordination and Katie Wearsch for assistance with pairing.
Euro Rabbit Housing | Allentown, Inc. | RBEURO-06 | Middle divider removed http://www.allentowninc.com/large-animal-housing/rabbit-ferret/ |
R-Suite Enriched Rabbit Housing | Techniplast | 2 attached single cages with middle divider removed http://www.tecniplast.it/en/product/r-suite-rabbit-housing-rack.html |
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Lab Animal Marker – Standard Tip | Ketchum Manufacturing | Blue http://www.ketchum.ca/products/lab-animal/animal-markers/1313/animal-markers-standard-tip |
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Western Timothy Hay | Oxbow Animal Health | http://www.oxbowanimalhealth.com/products/type/detail?object=1530 | |
Spray Bottles | Uline | S-18404BLU | https://www.uline.com/Product/Detail/S-18404BLU/Spray-Bottles/24-oz-Blue-Spray-Bottles |
Rabbit liners | Blue Ridge Tissue | Custom Versa-Pak T.1503 30'' X 30'' http://www.blueridgetissue.com/products/#versa_pak |
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Premium Full Leather Glove | Wells Lamont | 0-53300-07006-8 | https://www.wellslamont.com/catalog/product/premium-full-leather-glove/ |
Various Enrichment Toys | Bio-Serv | Multiple | https://www.bio-serv.com/category/Rabbit_Enrichment_Devices.html |
Fruit and Veggie Medley Dried Treats | Bio-Serv | F7227 | https://www.bio-serv.com/Rabbit_Enrichment_Treats/FVM.html |
White Noise Machine | HoMedics | https://www.amazon.com/HoMedics-SS-2000G-Relaxation-Machine-Nature/dp/B00A2JBMRE/ref=redir_mobile_desktop/134-0048439-0235364?_encoding=UTF8&keywords=white%20noise%20machine&qid=1503569413&ref_=mp_s_a_1_6_a_it&sr=8-6 | |
Safari Soft Bristle Cat Brush | Safari | https://www.amazon.com/Safari-Soft-Bristle-Brush-Cats/dp/B0002RJMB4 | |
Crink-l'Nest | The Andersons Lab Bedding | CNK | http://www.andersonslabbedding.com/irradiated/crink-lnest/ |
Manzanita Wood Gnawing Sticks | Bio-Serv | W0016 | http://www.bio-serv.com/Rabbit_Enrichment_Devices/W0016.html |
Wood Gnawing Blocks Certified | Bio-Serv | K3511 | Small http://www.bio-serv.com/Rabbit_Enrichment_Devices/Wood_Blocks.html |
Paper Bags | Duro | Sack Lunch Bags https://www.amazon.com/Duro-Paper-Lunch-Brown-Count/dp/B01N0AS7QO/ref=sr_1_9?ie=UTF8&qid=1511194982&sr=8-9&keywords=paper+bags |
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Various Sources of Cardboard | Recycled supply boxes from the vivarium | All cardboard is autoclaved prior to use |