Establishment of the Body Conditioning Score for adult female Xenopus laevis
The assessment of animals health and nutritional status using a Body Condition Score (BCS) has become a common and reliable tool in lab-animal science. It enables a simple, semi-objective, and non-invasive assessment (palpation of osteal prominences and subcutaneous fat tissue) in routine examination of an animal. In mammals, the BCS classification contains 5 levels: A low score describes a poor nutritional condition (BCS 1-2). A BCS of 3 to 4 is considered optimum, whereas a high score (BCS=5) is associated with obesity. While BCS are published for most common laboratory mammals, these assessment criteria are not directly applicable to clawed frogs (Xenopus laevis) due to their intracoelomic fat body instead of subcutaneous fat tissue. Therefore this assessment tool is still missing for Xenopus laevis. The present study aimed to establish a species-specific BCS for clawed frogs in terms of experimental refinement. Accordingly, 62 adult female Xenopus laevis were weighed and sized. Further, the body contour was defined, classified, and assigned to BCS groups. A BCS 5 was associated with a mean body weight of 193.3 g ({+/-} 27.6 g), whereas a BCS 4 ranged at 163.1 g ({+/-}16.0 g). Animals with a BCS=3 had an average body weight of 114.7 g ({+/-}16.7 g). A BCS=2 was determined in 3 animals (103 g, 110 g, and 111 g). One animal had a BCS=1 (83 g), which would be equivalent to a humane endpoint. In conclusion, individual examination using the presented visual BCS provides a quick and easy assessment of nutritional status and overall health of adult female Xenopus laevis. Due to their ectothermic nature and the associated special metabolic situation, it can be assumed that a BCS [≥]3 is to be preferred for female Xenopus laevis. In addition, BCS assessment may indicate underlying subclinical health problems that require further diagnostic investigation.