Advantages and Risks of Husbandry and Housing Changes to Improve Animal Wellbeing in a Breeding Colony of Common Marmosets (Callithrix jacchus)

Between 1975 and 2014, housing conditions for laboratory-housed marmosets changed dramatically after the introduction of new guidelines designed to improve their care and wellbeing. According to these guidelines, our facility provided marmosets with outside enclosures, switched to deep litter as bedding material, and discontinued the use of disinfectant agents in animal enclosures. However, both deep litter and access to outside enclosures hypothetically increase the risk of potential exposure to pathogenic microorganisms. We evaluated whether these housing and husbandry modifications constituted an increased veterinary risk for laboratory-housed common marmosets (Callithrix jacchus). After the animals had been exposed to these new housing conditions for 2.5 y, we examined their intestinal bacterial flora and feces, the deep litter, and insects present in the housing. In addition, we assessed the marmosets’ general health and the effect of outdoor housing on, for example, vitamin D levels. Although numerous bacterial strains—from nonpathogenic to potentially pathogenic—were cultured, we noted no increase in illness, mortality, or breeding problems related to this environmental microflora. Housing laboratory marmosets in large enriched cages, with both indoor and outdoor enclosures, providing them with deep litter, and eliminating the use of disinfectants present an increased veterinary risk. However, after evaluating all of the collected data, we estimate that the veterinary risk of the new housing conditions is minimal to none in terms of clinical disease, disease outbreaks, abnormal behavior, and negative effects on reproduction.The Biomedical Primate Research Centre (Rijswijk, The Netherlands) houses a self-sustaining breeding colony of common marmosets (Callithrix jacchus) for the purpose of conducting biomedical research on life-threatening human diseases. The marmoset colony was formed in 1975 and has been used mainly for research on autoimmune diseases, neurodegenerative disorders, and comparative genetics.^{3,5,6,14,21,29}After the introduction of new European and Dutch guidelines regarding animal care and welfare, animal housing conditions changed markedly between 1975 and 2014. Our facility responded promptly to these new guidelines, by providing larger and more complex cages comprising outdoor enclosures, each with an attached heated indoor enclosure, where the animals are housed in family groups to improve animal wellbeing.^22,35 The concept of environmental enrichment continued to be developed and optimized over the years.Potential benefits of outdoor enclosures are exposure to seasonal fluctuations in light and climate and increased sensory stimulation. These enclosures provide opportunities for exploration and manipulation that are considered to contribute positively to the animals’ wellbeing. Furthermore, marmosets housed indoors with no access to UV light are susceptible to metabolic bone diseases. Marmosets cannot synthesize vitamin D3 (cholecalciferol) from the plant form of the vitamin (ergocalciferol, vitamin D2). Without access to UVB radiation, they cannot form vitamin D3 from 7-dehydroxycholesterol in the skin.³¹ In addition to dietary supplementation with vitamin D3, we surmised that access to unfiltered sunlight in outside enclosures would limit or prevent vitamin D deficiency.Another change initiated in response to BPRC''s new housing guidelines was the cleaning of the housing facilities. Scent marking is an important aspect of the natural behavior of marmosets. In laboratory settings, marmosets scent-mark their cages constantly.¹¹ To minimize the removal of scents, disinfectants are no longer used to clean the enclosures. In addition to effects on scent, limiting disinfectant use could have other beneficial effects. For example, the chemical disinfection of their environment was suggested to be one cause of chromosomal disorders in marmosets.¹³A third important housing-related change was the provision of deep litter in the outdoor and indoor enclosures. Deep litter is a floor covering, preferably of organic origin, that promotes activities including locomotion, foraging, and playing. In general, the changes associated with providing deep litter typically involved a shift in the animals’ behavioral profiles toward those that might be observed in their wild counterparts; therefore, the provision of deep litter is seen as environmental enrichment.^{7,9,10,24,30,32}Although some of these changes have been implemented in zoos, primate centers that breed marmosets for research purposes have been more reticent because of potential health issues. To evaluate whether the new housing conditions enhance the animals’ wellbeing, we studied their benefits and potential threats to the animals, the practical consequences for personnel and management, and the influence on experimental results. In particular, the health risks for the marmosets due to increased microbiologic exposure because of the new housing conditions were examined. The aim of the study was to determine whether these changes in their housing constituted not only an improvement in their wellbeing but also a possible increased veterinary risk for laboratory-housed common marmosets.