Studies on the main chemical composition of bones

The femurs of 20 cows and 4 young animals have been analysed, similarly the tibias of 4 cows. The whole bone was used as a sample. Fat, protein and ash were directly determined and the water content was calculated as difference. By a visual estimate the animals were classified in grade classes using a system in which class I denotes very fat cows and class VII emaciated animals. The average percent composition of the cow femurs was as follows. The ranges of variation are given in brackets. A sick cow is omitted. Fat 33.6 (26.9—38.9), Protein 17.2 (15.0—21.6) Ash 34.8 (30.0—39.9), Water 14.4 (11.3—16.0) There seems to be a negative correlation between the fatness of the cow and the fat content of the femur. However, a closer examination of the results, and especially the examination of the volume-% composition of the femurs, suggests that the accumulation of fat in the bone results from the withdrawal of ash and protein which are the firmness and tenacity giving components in the bone. Probably the cows of the better grade classes have been in better condition not only as regards their fat deposits and musculature but also in regard to the minerals in the bones. Thus a high fat content in the bones is no positive indication of a healthy condition in an animal. The protein content in the femurs of young animals is about the same as that in cow femurs. The water content is high but that of fat and ash low. The femur of a newborn calf was almost fat-free, but the fat and mineral contents seem to increase rapidly already in early life. The investigated tibias contained more protein and ash but less fat than the femurs of the same cows. This study does not afford support to the opinion expressed e.g. by MAYNARD and LOOSLI (1 p. 126) that the fat in the bones the same manner as the adipose tissues in general, serves the animal as energy reserve during scanty feeding. The fat in the bones seems not to decrease when the animal becomes thinner but this probably occurs when the nutritional state pertaining to minerals and vitamins is improved.