Sheep were used to model the digestion of bone in the rumen. The model of ruminal bone digestion was used to identify a possible source of phosphorus and calcium for ruminants, with particular focus on giraffes. The daily requirements for phosphorus and calcium by giraffes to sustain skeletal growth and maintenance are large. The source of sufficient calcium is browse. The source of necessary phosphorus is obscure, but it could be via osteophagia, a frequently observed behaviour in giraffes. The possibility of ingested bone being digested in the rumen was assessed. Bone samples from cancellous and dense bones were immersed in distilled water, artificial saliva, and in the rumens of five sheep, for a period of up to 30 days. Distilled water had no effect on bones. Dense (metacarpal shaft) bone samples were softened by exposure to saliva and rumen fluid, but neither calcium nor phosphorus concentration was affected. Cancellous (cervical vertebrae) bone samples also softened and the mass and volume of the samples decreased over the period, especially as a result of exposure to saliva, but they also lost little calcium and phosphorus. In conclusion the use of sheep to model the possible rumen digestion of bone established that although saliva and rumen fluid can soften ingested bones, it is unlikely that ingested bone provides any significant source of minerals while in the rumen, for giraffes and ruminants in general. / Dissertation (MSc (Veterinary Sciences))--University of Pretoria, 2006. / Production Animal Studies / unrestricted

Apart from its slender appearance, four main factors lead to questions regarding the bone density, mineral content and morphology of the giraffe skeleton: X A rapid vertical growth rate ¡V especially in the neck and metapodials X Biomechanical considerations pertaining to the tall and slender shape of the skeleton X A proportionally larger skeleton in relation to body mass X A seemingly abnormal mineral balance in their diet with possible signs of mineral deficiency (i.e. osteophagia) In this study the skeleton of the giraffe was compared with that of the African buffalo with regards to bone density, skeletal calcium (Ca) and phosphorus (P) content and certain femoral and metacarpal morphological characteristics. The aim was to establish if, compared to buffalo, the features of the giraffe skeleton differed in any unique way. Fourteen similar bones or parts of bones were collected from carcasses of six adult giraffe bulls and nine adult buffalo bulls. These bones were cleaned, weighed and their volume determined through water displacement, from which their density could be calculated. Hereafter, Ca and P content were analysed in 10 bones from each carcass. Morphological characteristics of cross-sections from femoral and metacarpal shafts were also measured. No significant differences between the density or mineral content of bones in the two species could be found. In both species 19,5% Ca and 9,5% P were measured in defatted bone. Although similar in mineral concentration, the giraffe skeleton contains three times more absolute Ca and P, which translates into a 1,5-2-fold higher dietary requirement for these minerals compared to buffaloes. A gradation in the volume and weight of cervical vertebrae was also seen in giraffes. This could hold biomechanical advantage for the carriage and manoeuvrability of the long neck. Bone wall thickness of the giraffe femur and metacarpus is increased compared to buffaloes. This could hold biomechanical advantage for the slender legs that are subjected to increased vertical forces. Adequate Ca seems to be acquired through very specific browse selection, which seems to be of evolutionary origin, while the acquisition of adequate P seems to be critical and a possible cause for osteophagia. This study is the first of its kind in these species and therefore also provide valuable baseline data for future work in this field. / Dissertation (MSc (Veterinary Science))--University of Pretoria, 2004. / Production Animal Studies / unrestricted