Body condition scoring facilitates healthcare monitoring in Hermann's Tortoises (Testudo hermanni ssp.)

Abstract

Clinical assessment of body condition is crucial in captive and free-ranging reptiles, since a large percentage of diseases result from inadequate nutrition. However, preventive health care is restricted by the lack of a practical method for the assessment in tortoises. Pre-existing evaluation systems based on weight and shell measurements are laborious and ignore the clinical presentation of the animal. The present study aimed to facilitate the assessment by establishing a body condition score. A total of 373 Hermann's Tortoises (Testudo hermanni) (n = 281 tortoises kept as pets in Germany and n = 92 tortoises originating from a free-ranging population (68) or a rearing station (24) in France) were examined and data (weight (g), carapace length (cm), width (cm), height (cm)) were recorded in a standard protocol between October 2020 and October 2021. A modified version of a body condition score for Mojave Desert Tortoises (Gopherus agassizii) (1 = cachectic, 3 = ideal, 5 = obese) was utilized and tested against pre-existing shell measurement systems (Jackson's ratio, body condition index, volume condition index, circumferential product). German captive tortoises were significantly heavier and larger than French specimens. In the Spearman's correlation matrix, the body condition score showed a statistically significant correlation with all measurement methods in the total population of captive tortoises (Testudo hermanni boettgeri), with a medium correlation strength, and a lack of correlation in free-ranging tortoises (Testudo hermanni hermanni). However, individual animal data suggested misleading results of mathematical equations in terms of body condition. Clinical evaluation of tortoises, including a body condition score, should be considered essential to provide good healthcare and should be an integral part of general examination.

Fig 1. Hermann’s Tortoise with marked measurement points.

Straight carapace length (from nuchal notch to caudal notch) demonstrated with the red line, carapace height and width (at the level of the third vertebral scute) demonstrated with the blue line and curved carapace and plastron circumference demonstrated with the green line.

Fig 2. Adult Hermann’s Tortoises with different body condition scores (BCS).

From left to right: BCS 2.0, BCS 2.5, BCS 3.0, BCS 4.0, BCS 4.5. Notice the deep withdrawal into the shell (arrow) and the muscle atrophy in the forelimbs (circle) of the tortoise in poor condition (BCS 2.0), compared to the tissue bulk around the neck and shoulders (arrow) and prominent muscle mass in the forelimbs (circle) of the tortoise in high condition (BCS 4.5).

Fig 3. Adult Hermann’s Tortoises with different body condition scores (BCS).

Tortoises in poor (left, BCS 2.0), good (center, BCS 3.0) and high (right, BCS 4.5) condition showing the difference in tissue bulk around the axillar region between these condition categories (circle).

Fig 4. Data visualization in the spearman correlation matrix of the total population.

Spearman correlation coefficient rho is indicated in gray (total population), pink (Testudo hermanni boettgeri) and blue numbers (Testudo hermanni hermanni), p-values are indicated by stars: * = p < 0.05, ** = p < 0.01, *** = p < 0.001.

Fig 5. Violin plots of variance distribution of weight in male and female German tortoises.

Individual data points are distributed as colored dots within each category, with the box indicating the middle half of the data set and the width of the box expanding with the number of data points. The median values are shown as red dots.

Fig 6. Violin plots of variance distribution of carapace length in male and female German tortoises.

Individual data points are distributed as colored dots within each category, with the box indicating the middle half of the data set and the width of the box expanding with the number of data points. The mean values are shown as red dots. This effect was also seen in French tortoises, where female tortoises were significantly heavier (females: mean 816.53 ± 192.24g, males: mean 423.69 ± 111.08g) longer (females: median 15,96 ± 1,57cm males: median 13.05 ± 1.51cm), broader (female: median 11.84 ± 0.95cm, males: median 10.26 ± 1.04cm) and higher (female: median 8.13 ± 0.59cm, males: median 6.58 ± 0.53cm) than their male counterparts (Figs 7 and 8).

Fig 7. Violin plots of variance distribution of weight in male and female French tortoises.

Individual data points are distributed as colored dots within each category, with the box indicating the middle half of the data set and the width of the box expanding with the number of data points. The mean values are shown as red dots.

Fig 8. Violin plots of variance distribution of carapace length in male and female French tortoises.

Individual data points are distributed as colored dots within each category, with the box indicating the middle half of the data set and the width of the box expanding with the number of data points. The median values are shown as red dots.