Message Number: YG5327 | New FHL Archives Search
From: RRC
Date: 2001-07-10 08:54:00 UTC
Subject: Re: my ferret died...I need major advice

"Lisa Shortley" asks:

>If eggshells are not digestable, why are they reccommended to use for
>chicken gravy? i thought ferrets were able to get calcium or
>something of use from them?

Since I designed Bob's Chicken Gravy, I guess I should answer this one.
Eggshells are a calcium carbonate compound (CaCO3) and are not exactly
digestible by most mammals. By digestible, I mean they are not totally
dissolved nor significantly changed within the stomach or bowel. But a
small portion of the outer, exposed surfaces of the eggshell subjected
to stomach acid *ARE* dissolved while in the stomach, forming free
calcium ions (calcium carbonate is generally considered a mild antacid
and readily reacts with stomach acid). Because the amount of calcium
ions produced are limited by the length of time the eggshells are in
stomach acid (this assumes size of eggshells, body temperature and pH of
stomach acid are standardized), those reactions are limited in animals
with rapid stomach emptying times, such as the ferret. So, in ferrets,
eggshells are not very digestible.

Food in the ferret's stomach is only there for very short period of
time. Ferrets are small, long animals with very high energy
requirements, which means they have to move food through their
gastrointestinal tract very rapidly in order to consume enough to
survive (there are tiny insectivores which have a stomach capable of
dissolving food almost as fast as it is being swallowed; their stomach
emptying time is only a few minutes after the filling time). This is one
reason why a ferret has an average gastrointestinal emptying time of
just 4 hours; that stuff has to move through FAST to make room for the
next load. You simply cannot eat enough unprocessed vegetable matter to
supply those high metabolic needs, which is one reason why ferrets are
primary, obligate carnivores; only the concentrated nutrients in animal
flesh can meet their high energy and nutritional requirements (PROCESSED
starches in extruded dry or kibbled foods can met caloric requirements,
but how many polecats carry pots and matches to make oatmeal?). While
some animals with much longer gastric emptying times can digest
eggshells far better than ferrets, few mammals can digest them
completely unless the shell's surface area is vastly increased by
grinding them to dust (which is how the antacids are made).

There are several types of calcium ions depending on how many electrons
have been stripped off the outer valence shells, but the calcium ion
released by eggshells are of a type which are quite easily absorbed by
the body (they are reported to be absorbed better than the calcium
stripped off digested bones). Since the total amount of calcium
available for absorption is regulated by the length of time of reaction,
surface area, temperature, and strength of stomach acids, in a normal,
healthy ferret, the calcium absorbed from eggshells is—on average—rather
small. You can increase the rate of reaction by increasing temperature,
which is not possible with ferrets because it makes them so hot under
the collar. You could also try increasing surface area of the eggshells
by making them smaller, keeping the eggshells in the stomach for a
longer period of time, or by decreasing the pH of the stomach acid. If
you assume most ferrets would react negatively to being heated up,
having their gastric transit time slowed, or their stomach acids
increased in strength, that leaves surface area as the best way for
increasing calcium absorption. The trouble is, while smaller fragment
have faster rates of reaction, how would I know exactly what size the
people in New York are making their eggshells? Or in California? Or in
that vast wasteland called Missouri?

I get around it by standardizing everything, then allowing the rate of
reaction to be controlled by temperature and time during cooking. Fresh
chopped chicken has a pH between 5 and 6 during boiling, depending on
the amount of fat and the point during cooking when the measurement is
taken (yes, I DID test it). This is acidic enough to dissolve the outer
surfaces of the eggshells during cooking (not the complete eggshell;
only the surfaces exposed to the acidic water. This is exactly the same
thing that happens when acid rain drips on marble, or carbonic acid
dissolves limestone to form caves). I increase the rate of reaction with
heat, which is one reason I recommend boiling (controls the
temperature). So, following the directions for making Bob's Chicken
Gravy allows for the calcium levels of the food to be increased a tiny
bit without worrying if the ferret is going to pick out the eggshells,
if a sick ferret can dissolve calcium as rapidly as a healthy ferret,
and without worry of accidentally messing up the calcium/phosphate ratios.

Normally, just adding calcium to the diet is dangerous because it MUST
remain in balance with the total phosphates in solution within the blood
and liquid portions of the body. If the calcium/phosphate ratio is not
maintained, it can cause severe stress to various organ systems (and
other painful problems: if you have ever had tetany, you learn you do
not want low blood calcium levels. Low calcium is also linked to
increased kidney and bladder stone formation). It can also cause the
body to dissolve bone to supply the missing compound. Remember, bone is
a protein matrix filled with tiny crystals of hydroxyapatite, which is a
form of bone calcium phosphate (Ca3(PO4)2 = tribasic calcium phosphate =
tricalcium phosphate). The skeleton is where the body STORES calcium
phosphates, so when the total calcium (or phosphate) in the blood drops,
bone is dissolved to make up the difference. Because there is so much
bone compared to the amount circulating in the blood, a chronic calcium
or phosphate malnutrition may go completely unnoticed until the bones
become so weak they bend (as in rickets) or begin to fracture, which is
why many natural diets are so risky. By the time you notice a problem,
it is a problem difficult (or impossible) to fix.

Personally, I would NEVER recommend that anyone just add extra calcium
or phosphate to the diet (unless prescribed AND monitored by a
veterinarian!) for just those reasons (there are MORE reasons I will not
delve into). The reason I use eggshells in the chicken gravy recipe is
because the chickens used are immature (which is true of nearly ALL
store-bought whole chickens). Immature chickens have bones which are not
totally ossified, which means they are lacking in calcium. This SLIGHTLY
skews the calcium/phosphate ratio. So I add eggshells, which only add a
very tiny amount of calcium to the diet; just enough to help control for
the extra phosphates in the immature chickens. Since I am only relying
on surface area reactions to supply the extra calcium, and since the
calcium absorbed is minor, it is not nearly as dangerous as asking
people to add X micrograms of calcium to Y liters of total volume. This
is especially true after seeing so many ways people have monkeyed around
with the original recipe. There was NO WAY I wanted to read an email
which accused me of overdosing some ferret on calcium, based on a friend
of a friend of a friend's potion which changed my original recipe and
increased calcium a hundredfold by adding calcium rich supplements. With
eggshells broken into tiny bits, I can figure the rate of reaction
during cooking and digestion and make sure the calcium added does not
exceed the ratio for the phosphates present. Cooking adds far more
calcium to the mixture than what is absorbed through stomach acid
digestion alone (which is rather minimal in ferrets), and both together
do a pretty good job of balancing the Ca/P ratio (which I have also
checked; if my recipe is followed EXACTLY, if using distilled water, the
final Ca/P ratio should be between 1:1 and 1.6:1, depending on the exact
chicken used).

If you have noticed the complexity of designing a food formulation with
an eye on meeting the ferret's nutritional needs, you start to
understand how adding something as simple as an eggshell to the mixture
can influence the final result. Maybe you can better understand the
great job Dr. Willard did with Totally Ferret. Or why I am so reluctant
to use most duck soup concoctions; they may help one problem but cause
another. Thus, I STRONGLY support Dr. William's suggestion to only use
chicken (or turkey) baby foods to hand feed sick ferrets. I can be
pressed into adding some whipping cream IF I AM SURE the extra fats
don't stress the ferret more than they help. I readily thin chicken baby
food with Pedialyte, but other than that, I add nothing. Because of
their small size and extreme energy and nutritional needs, even normal,
healthy ferrets can rapidly become stressed because of nutritional
imbalances and/or deficiencies. I have seen some duck soup recipes which
are so complex you have to wonder what is happening biochemically. Some
recipes include herbs containing powerful phytochemicals which may react
with prescribed medications, or may have one effect in humans, but an
unknown one in ferrets. Nutritionally, I understand chicken baby food
doesn't provide for complete nutrition, but in almost every case, the
ferret recovers and can make up deficiencies, or the use is a short term
one because the ferret doesn't survive. In those few instances where a
ferret needs the diet for a long period of time, just adding ground dry
ferret food negates the problem of nutritional deficiency.

I hope this helps.

Bob C