In the submitted study it was endeavoured to determine the optimal calcium content in the forage of Greek tortoises.
For this purpose fodder was offered in two trials, each time with different amounts of calcium and the same amount of phosphorus. In the first sequence four groups with a Ca ¿ content of 1.3 %, 1.9 %, 3.2 % and 3.8 % were formed, P ¿ content was 0.7 %. In the second sequence two groups with a Ca ¿ content of 1.1 % and 3 % were formed, the P- content was the same as in the first sequence. By most species the main way of excreting calcium is by means of defacation, therefore faeces, collected for the simultaneously made digestibility experiment, were collected for different lengths of time and later analysed. For the purpose of detecting calcium, magnesium, phosphor and alkaline phosphatase in the blood, five tests were made. An additional examination by means of X-ray and CT had the purpose of pointing out changes referring to the shell and the skeletal system after adding varying concentrations of calcium to the fodder. The x-rays were taken as a basic pair of pictures with dorsoventral and laterolateral i. e. craniocaudal views were taken.
By means of the CT exposure, density (thickness) of definite parts of the skeleton or carapace were measured. In the submitted study the digestibility of raw nutrients and minerals was very high ¿ and comparable to the results of other authors. The apparent digestibility of calcium was very high in all of the groups, independent of its contents in the fodder, and reached an average of 90.61 %. A calcium content of 3.8 % in the fodder led to calcification of the kidneys by two animals and resulted in their death, which then led to the decision to finish this group. Through the blood tests the works of different authors, regarding the seasonal variability of calcium and alkaline phosphatase were confirmed.
The concentration of calcium in the blood increased constantly beginning in spring and continued until fall, a difference between males and females however must be considered. In the case of the alkaline phosphatase an increase in spring can be noticed, it reaches a maximum in summer, which is followed by a decrease in fall. The phosphor- and magnesium content in the blood also decreased in fall.
The x-rays showed inhomogeneity within each specific group on the one hand and also between the two distinct groups. The x-rays could not show significant differences whether before nor after the feeding. The CT-exposures however by measuring the density of the capiti ossa humeri showed a significant difference between the groups A and B at the beginning of the experiment, which at the end of the experiment however was no longer evident. A significant increase of density of the third neural plate was noticed in group B at the end of the experiment. A significant increase of density of the third neural plate and also radiographically visible imbalances in mineralization were noticed in group B at the end of the experiment.
The apparent digestibility of calcium by young Greek tortoises is unexpectedly high ¿ a very important aspect which is to be considered by their keeping. Over supplementation ¿ above 3.8% - can cause calcium to accumulate in the kidneys, which will cause the animal to die. In a prior study at the Institute of nutrition (VUW) the effect of protein content and humidity in fodder already could be proofed.
The influences on bone and shell growth depend on many factors. Calcium in the nutrition, however plays an undisputed important role. It must be supplemented sufficiently ¿ especially in the case of young animals, which require larger amounts of calcium.