Influence of environmental humidity and dietary protein on pyramidal growth of carapaces in African spurred tortoises (Geochelone sulcata)

Abstract

The carapaces of captive-raised tortoises (terrestrial chelonians of the zoological family Testudinidae, often develop pyramidal-shaped osseous growth centrally within the horny plates. With very few exceptions (e.g. Geochelone elegans, Psammobates sp.), this conical growth pattern is considered to be pathologic. This very common defect is believed to be an important indicator of the quality of captive tortoise management. This study was designed to examine the effect of dietary protein level and environmental humidity on the degree of pyramidal growth in the carapaces. Fifty recently hatched African spurred tortoises (G. sulcata) were raised for 5 months under artificial conditions of varying environmental humidity and dietary protein content (14% vs. 19% vs. 30% crude protein in dry matter). Humps of the carapaces that developed and blood values of calcium, phosphorus and haematocrit were measured and compared among groups. Dry environmental conditions (24.3-57.8% and 30.6-74.8% relative humidity) produced taller humps than humid conditions (45-99% relative humidity). Hump formation differed significantly (p < or = 0.001) between these three groups kept under different humidity conditions. Variable dietary protein had a minor, positive impact on this pathological formation of humps (pyramidal growth syndrome, PGS). Analysis of blood (calcium, phosphorus and haematocrit) offered no further explanation as to the development of the humps.