Phosphorus and calcium extraction from bone digestion in the rumen of sheep (Ovis aries)

Abstract

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.