There is another danger to small carnivores, especially those that are
primary, obligate flesh eaters like ferrets.  Fat and muscle break down
into acidic compounds, such as ketones, fatty acids, and amino acids that
can lower blood pH (make it acidic).  Biochemical reactions are only
efficient at a narrow pH range, so it is very important for the body to
react quickly if the blood becomes abnormally acidic or alkaline.  If
the change in pH is minor, circulating buffering agents (among other
mechanisms) in the blood help maintain a proper pH.  If buffers in the
blood are used up, then the body resorts to a number of other solutions,
including the cannibalizing of bone to create new buffers.  If a steady
supply of calcium and phosphates are available, then skeletal bone
remains more-or-less untouched.  If not, then minerals will slowly leach
out of the skeleton.  While this type of bone mineral leeching is not
as common in large predators, small carnivores like the ferret have
small blood reserves, placing them at risk of osteoporosis.  Think of
the problems caused by diet and its relationship to osteoporosis in
post-menopausal women, and apply that knowledge, multiplied by several
factors of risk, to neutered ferrets lacking significant reserves of
blood-buffering agents.  It is no wonder more than half of the pet
ferret skeletons I've examined display moderate to severe osteoporosis.
Ferrets need a constant source of natural blood buffering agents to
maintain a healthy skeleton.
 
It is fortunate for small carnivores that prey animals come equipped
with a natural buffering agent: hydroxyapatite.  This is a crystalline
compound composed of various mineral salts, primarily calcium phosphate.
Mammals are full of the stuff.  Hydroxyapatite is strong and stable; so
much so it is quite common to find deposits of the mineral long after the
death of the animal.  We call these deposits "bones." Hydroxyapatite is
the mineral part of bone--very strong, relatively lightweight, and HIGHLY
reactive to acid.  This last remark cannot be overemphasized.  Bone
mineral is so highly reactive to acid that if you suspend a chicken bone
in a liter of Coke and come back a week later, the bone will have lost so
many bone minerals that it will become rubbery, easily crumbling between
your fingertips.  Thousands of physiology students have soaked a cow bone
in a tray of acid, only to come back to find a bone so rubbery that it
can be tied in a knot.
 
This point is extremely important to carnivores that regularly consume
bone.  You might even conclude that without it, few animals could pursue
a carnivorous lifestyle.  Without such reactivity to acid, bone would
remain sharp and pointed, and could slice into tissue, or poke through
gastrointestinal walls.  Fortunately for carnivores, stomach acid (and
the mechanical effects of gastric contractions) quickly rounds prickly
points, dulls sharp edges, and even significantly reduces the overall
mass of the bone fragment, leaving behind a smooth polish sometimes
interpreted by some obtuse archaeologists as proof of human tool making.
In the case of the ferret, larger cortical bone fragments aren't in
the stomach long enough to completely dissolve, but a few minutes in
a churning stomach filled with acid and the bone becomes smooth and
polished, effectively rendering it safe for passage to the nearest corner
pile.  Smaller particles have a proportionately larger ratio of surface
area to internal volume, allowing more acid to contact the bone, so they
dissolve faster.  The same is true about very sharp or pointed
surfaces--the bone will actually dissolve faster along edges and points
compared to flat bone surfaces.  This literally "rounds off" the edges
and points of a bone fragment, significantly decreasing the chances of
gastrointestinal injury.
 
There is one more clue on this trail of gastronomic physiology.  Some
people may doubt the efficiency of gastric acid to dissolve bone,
rendering fragments safe.  ALL mammals use hydrochloric acid, secreted by
special cells called osteoclasts, to resorb, remodel, and remove bone.
Bone is very vascular, and when it is broken, it bleeds, forming a blood
clot around the broken ends.  This clot hardens, forming a callus, which
ultimately ossifies into bone.  The problem is the callus can be bumpy,
have bits of bone sticking out, or even be so large it interferes with
the movement of muscles.  Hydrochloric acid comes to the rescue as
unneeded parts of the bone are etched away by osteoclasts.  Gastric
acid is, interestingly, also hydrochloric acid.  The same acid the body
uses to reshape, remove, and restore bone is also the acid secreted by
the stomach.  It takes time to remodel a bone callus (how fast can
microscopic cells work?), but the stomach secretes a considerable amount
of acid at one time.  There is no doubt the hydrochloric acid produced in
the stomach can and will dissolve bone.  The only parts it can dissolve
are those that are exposed, which include the sharp points and edges.  If
the sharp points and edges are dissolved, how can the bone be a danger?
 
Bob C
[Posted in FML issue 4157]