Osteophagy

Osteophagy is the practice in which animals, usually herbivores, consume bones. Most vegetation around the world lacks sufficient amounts of phosphate.^[1] Phosphorus is an essential mineral for all animals, as it plays a major role in the formation of the skeletal system, and is necessary for many biological processes including: energy metabolism, protein synthesis, cell signaling, and lactation.^[2] Phosphate deficiencies can cause physiological side effects, especially pertaining to the reproductive system,^[1] as well as side effects of delayed growth and failure to regenerate new bone.^[2] The importance of having sufficient amounts of phosphorus further resides in the physiological importance of maintaining a proper phosphorus to calcium ratio. Having a Ca:P ratio of 2:1 is important for the absorption of these minerals, as deviations from this optimal ratio can inhibit their absorption.^[3] Dietary calcium and phosphorus ratio, along with vitamin D, regulates bone mineralization and turnover by affecting calcium and phosphorus transport and absorption in the intestine.^[4]

It has been suggested that osteophagy is an innate behavior that allows animals to supplement their phosphorus and calcium uptake in order to avoid the costly effects of deficiencies in these minerals.^[1] Osteophagic behavior has been observed in pastoral and wild animals, most notably ungulates and other herbivores, for over two hundred years.^[1] Osteophagy has been inferred from archaeological studies of dental wear in Pleistocene fossils dating back 780,000 years.^[5] It has been seen in domestic animals, as well as red deer, camels, giraffes, wildebeest, antelopes, tortoises, and grizzly bears.^[5] Due to differences in tooth structure, herbivores tend to chew old dry bones that are easier to break, while carnivores prefer to chew softer fresh bones.^[6] Variations of the behavior have also been observed in humans.^{[citation needed]}

While osteophagy has been regarded as a beneficial behavior to combat mineral deficiencies in animals, osteophagic practices have also been observed to be detrimental to the dentition of herbivores. It has been observed that the pattern of wear on the cheek teeth of herbivores is congruous to the manner in which herbivores hold and chew bones.^[5] A major cost of osteophagy is therefore significant wear on teeth and dental breakage in herbivores, whose teeth did not evolve to enable the regular consumption of hard materials but rather for the grinding of vegetal fibers.^[5]