Re: Can humans digest bone from livestock, poultry?

Humans can, Mike, and as with so many things, the fact that 20/21st 
century westerners choose not to do so is no reason to knock it.  Bones 
are swallowed by many kinds of carnivorous animals and birds, and always 
undergo some degree of digestion, but large pieces are rarely completely 
dissolved.  

Bone is a complex substance, with two main chemical components.  These are 
calcium phosphate, or more properly the mineral hydroxyapatite, and 
collagen, the organic, protein component.  Each of these substances is 
attacked by the acid and other digestive juices in animal guts, but 
different species produce different effects upon the bone.  Owls and other 
birds of prey usually swallow their prey, but cast up the bones after a 
short time in the stomach.  Such cast up bones look perfect to the naked 
eye, but under a microscope pitting and rounding can be seen as the first 
stages of dissolution.   Bones form a significant proportion of the diet 
of hyaenas, and they are consequently adapted for this, with powerful jaws 
and teeth to crack the bones of large animals.  Their digestive system has 
a substantial effect upon the bone they swallow and sharp fragments of 
thick limb bones end up rounded, looking rather like well-used cakes of 
soap.  Dogs come somewhere in between owls and hyaenas in their ability to 
digest bone.  It is of course easy to check for yourself what happens to 
steak bones eaten by you or your dog, but requires some dedication to the 
spirit of scientific enquiry.  Such studies have been carried out, most 
notably by Dr Andrew 'Bone' Jones of the University of Bradford.  A 
reference to one of his papers is given below.

Not only carnivores gnaw bones, and some of the gnawed antlers you have 
found in the woods have probably been attacked by rodents or deer.  They 
do not have teeth or guts adapted to deal with bone fragments, but by 
patiently gnawing at the bone with their incisors can remove bone which 
would be powdered and easy to digest.  Such herbivores are probably eating 
bone to obtain additional calcium, which can be critical for a pregnant or 
lactating herbivore, or a stag growing his antlers.   Serious bone-
devourers such as hyaenas probably obtain significant amounts of fat and 
protein from fresh bones, especially the marrow.   Most contemporary human 
diets contain ample calcium.

The study of the changes which happen to bones between death and burial is 
called taphonomy, a specialist topic within archaeology and forensic 
science.  The key text on this subject is Lyman's book.

Jones, A.K.G. 1986. Fish bone survival in the digestive systems of pig, 
dog and man, in D. Brinkhuizen & A Clason (eds.) Fish and Archaeology. 
Oxford, British Archaeological Reports International Series 294: pp53-61

Lyman, R.L. 1994. Vertebrate Taphonomy. Cambridge University Press.

O'Connor, T.P. 2000. The Archaeology of Animal Bones.  Sutton Publishing.