Linear regression model of BCS ~body weight.

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 housing refinement in lab-animal facilities. 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), equivalent to a humane endpoint. In conclusion, individual examination using the presented visual BCS provides a quick and easy assessment of the 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.</div

Fig 4 -

A. Violin plot of variance distribution in each BCS class. The violin plot shows the compact distribution of data in each BCS class. Individual data points are jittered within each category. The mean body weight values are also offered as red dots, and the error bars represent 1000-fold bootstrapped 95% confidence intervals. B. Scatterplot showing the body weight vs. the nose-cloaca distance color-highlighted by BCS classes. The linear trend in the data (βbw = 0.02, SE = 0.002, p2adj = 0.665) is indicated by the linear regression line with a 95% confidence band.</p

Five classes of body condition score assigned by body weight (g).

Five classes of body condition score assigned by body weight (g).</p

Effect of housing on BCS.

Housing conditions were analyzed with linear regression, in which the dependent variable (BCS) was modeled as a function of the housing condition. (DOCX)</p

Dorsal section of <i>Xenopus laevis</i> and assignment to BCS 1–5, red line in BCS1 indicates the nose-cloaca distance.

Dorsal section of Xenopus laevis and assignment to BCS 1–5, red line in BCS1 indicates the nose-cloaca distance.</p

Fig 5 -

High-grade lymph sac edema prior (A) and post puncture (B) of the same specimen, (C) drained clear punctate in syringes. Difference between BCS 5 and pathological lymphatic sac edema: Lymphatic sac edema is indicated by an apparent retraction of the skin between the eyes (see blue marks upper row); skin on the back and thighs shows wave-shaped movements when the frog in question swims due to the edema fluid; the frog swims more sluggishly; no impairment of food intake; clear secretion is drawn off during puncture, and lymph sac collapses again immediately (see blue arrows lower row).</p

Fig 3 -

Close-ups pictures of BCS 1: A: dorsal view, B and C: ventral and latero-ventral view, D: lateral view. Humane endpoint: Frog emaciated (—): rectangular body shape; raised abdominal contour and flat dorsal contour; bony structures of the thorax as well as pelvis prominent in ventral view; lower side of the mouth with concave curvature (sunken); skinny limbs firmly set off from trunk; humane endpoint reached.</p

Linear regression model of nose-cloaca length ~bw + bw:BCS.

Linear regression model of nose-cloaca length ~bw + bw:BCS.</p

Chart of body condition score.

Chart of Body Condition Score for adult female Xenopus laevis. (DOCX)</p

Lateral section of <i>Xenopus laevis</i> and assignment to BCS 1–5.

Lateral section of Xenopus laevis and assignment to BCS 1–5.</p