From:
"Church, Robert Ray (UMC-Student)"
Date: 2002-07-12 19:08:32 UTC
Subject: Bob C: Vitamin A and CD-5
To: <ferrethealth@smartgroups.com>
Cc: "Church, Robert Ray (UMC-Student)" <rrc961@mizzou.edu>
Message-ID: <43C5FBB91EB9CC468627C2BCB23391D32B9CA2@TIG-MAIL2.tig.mizzou.edu>
5. What is the exact tie of Vitamin A to ferret nutrition and overall heal=
th? Don't better ferret foods meet the nutritional needs of ferrets?
I hate to burst any bubbles here, but NO commercially available food meets =
100% of the nutritional needs of ferrets, despite the ads claiming otherwis=
e. Why, you ask? Because no one has a full understanding of ferret nutrit=
ional requirements. You cannot make a food that is 100% complete until you=
understand what =93100%=94 means. Consider, for a moment, the nutritional=
needs of humans. For more than a century, nutritionists have been careful=
ly looking at human diet, and they still don=92t fully understand HUMAN nut=
ritional needs. For example, the proper levels of Vitamin A in humans is s=
till under debate by nutritionists. The nutritional needs of ferrets have =
only been studied for only a brief moment in time, and are now only minimal=
ly understood as generalizations, not as necessarily as specifics. For ins=
tance, we know ferrets require high levels of fat in their diet, but not WH=
Y they do. Is it because ferrets require specific fatty acids, or the fat-=
soluble vitamins contained within them, or both? Does a high fat diet help=
overcome the problems of protein glucogenesis (creation of glucose from pr=
otein)? Ferrets have extremely rapid bowel transit times, and fats are ver=
y difficult to digest; do high fat requirements reflect purely biomechanica=
l needs? See what I mean? Ferret nutrition is currently a =93black box;=94=
we have a generally reliable understanding what a bad diet is, but it is h=
ard to say what an optimal diet constitutes. If we use human nutrition as =
our model, it will be another century before we begin to get a handle on th=
e problem, assuming we spend as much effort and cash on the investigation.
Modern ferret foods are compromises. On one hand, we understand whole carc=
asses of lagomorphs, rodents, birds, reptiles, and amphibians collectively =
constitute a perfect diet; after all, ferrets are domesticated polecats, an=
d polecats evolved over millions of years successfully surviving and reprod=
ucing while consuming this diet. They are specifically adapted to it. On =
the other hand, with dry, extruded foods we have a product that doesn=92t r=
equire killing numbers of small animals, nor picking up the bits of feather=
s, skin and bones left behind by our carnivorous pets, not to mention the o=
dor of the rotting parts the ferrets have hidden away =93for later.=94 Dry=
, extruded foods have little odor, they stay =93fresh=94 for long periods, =
and they don=92t force ferret owners into the unenviable position of becomi=
ng home butchers of small animals. Dry, extruded foods are a compromise be=
tween convenience and nutritional needs. They are only as good as our unde=
rstanding of those dietary requirements, never more.
No one seems to know what the actual dietary requirements for Vitamin A are=
in ferrets. We can assume that because ferrets, as domesticated polecats,=
are primary, obligate carnivores they would not have evolved mechanisms fo=
r obtaining the nutrient from yellow, or leafy green vegetables. Nor would=
they have access to domestic cows, so butterfat would not constitute a maj=
or source. That leaves the natural sources of Vitamin A available to ferre=
ts (polecats) being within the fats found in the brains, livers, and from b=
ody deposits and marrow of prey species. We can read species accounts of p=
olecats and historic documents of ferrets, and recognize they consume the p=
arts of animals containing the highest content of fats first (=3D optimal c=
arnivory). This only confirms what we already know; ferrets have high fat =
requirements.
The big question is, =93are the fats included in modern dry, extruded foods=
optimal for our ferrets?=94 We understand ferrets need about 30% fat in t=
heir diet, but what type of fat is required and why? Nutritionally, fat is=
an excellent source of energy, but so are carbohydrates, being in essence =
long strings of sugar. Because of this, the assumption is made that ferret=
s need fats for energy, assuming carbohydrates are an acceptable alternativ=
e, forgetting ferrets can manufacture their entire glucose needs entirely f=
rom protein with no ill effects. Well, yes, it is true that as energy sour=
ces, carbohydrates are as good as fats--not as concentrated, but just as go=
od. After all, glucose is glucose, regardless of the source. Still, there=
is an important dissimilarity between fats and carbohydrates. The differe=
nce between the two is that fats contain many important micronutrients, whi=
le carbohydrates contain, well, sugar. It is simplistic to assume energy i=
s the sole, or even primary reason ferrets require fat.
Ferrets probably require their high fat content for many reasons; I=92ll di=
scuss four in no particular order. First, they need it as a supplementary =
source of energy; polecats have little access to highly refined and cooked =
carbohydrates. Mind you, ferrets and polecats can completely meet their en=
ergy needs by converting protein to glucose, but the energy from fat is mor=
e than welcome. Second, they need a high fat content because they have suc=
h short bowel transit times, and fat digestion is notoriously difficult. T=
hird, large, complex brains like those residing in ferret skulls require la=
rge amounts of specific fatty acids in order to function correctly. The in=
clusion of fatty meat into human diet is credited with spurring the evoluti=
on of our brain. Lastly, they need it as a source of essential fatty acids=
, as well as fat-soluble vitamins (Vitamins A, D, E, K), and other micronut=
rients.
The question of the importance of fat for energy deserves additional discus=
sion. Suppose the only reason fat is needed by ferrets was for energy. If=
that were the case, then replacing fat with some other energy source would=
eliminate fat as a dietary requirement. For ferrets eating dry, extruded =
foods, such is already the case. Dry ferret foods use carbohydrates as a b=
inder, which requires them to be composed of significant amount of carbohyd=
rates; 40% or more of the total content. That represents a source of energ=
y that would negate the need for fat if energy were all that was needed. H=
owever, even in the presence of abundant available energy, ferrets STILL re=
quire a large amount of fat in their diet. If not for energy, then why is =
fat required in the ferret diet? I suspect short bowel transit times, and =
essential fatty acids and fat-soluble vitamins are the paramount reasons. =
If the need for fat is NOT for energy, then it must be for the nutrients it=
contains; long and short chain fatty acids, minerals, trace nutrients, and=
fat-soluble vitamins. Vitamin A is such a nutrient.
Vitamin A is a universal mammalian nutrient; that is, regardless of species=
, all mammals require it for good health. Vitamin A does just about the sa=
me thing in mammals regardless if they are human or ferret. If differences=
exist, they are from how the vitamin is obtained (plant v. animal), or in =
the amounts required, not on how it is utilized by the body. First, and fo=
remost, Vitamin A, or retinol, is required for proper eyesight. Retinol is=
first converted into retinal (the aldehyde form), which then combines with=
the protein opsin to form rhodopsin (or visual purple). Rhodopsin is an i=
mportant part of the composition of the rod cells of the retina, and is res=
ponsible for visual dark adaptation. Ferrets are specifically adapted to h=
unting in the dark, so they have retinas that predominately contain rods. =
When light interacts with rhodopsin, the molecule is split, generating an e=
lectrical impulse sent to the brain. Splitting rhodopsin destroys some ret=
inal, so a constant supply is required to replace the loss of visual purple=
. This is why one of the first symptoms of Vitamin A deficiency is the los=
s of night vision.
Vitamin A is also required to maintain epithelial tissue, so it is necessar=
y for the proper maintenance and function of the cornea, all mucous membran=
es, the lining of the respiratory and gastrointestinal tract, the bladder a=
nd urinary tract, and the integument (or skin). Vitamin A is necessary for=
proper bone growth and formation, and, historically, considered a =93growt=
h vitamin.=94 It is also important in preventing some epithelial cancers, =
especially those of the skin. Vitamin A has an important role in the maint=
enance of the immune system, and is necessary for the synthesis of proteins=
and compounds that inhibit the formation of tumors. It has recently been =
discovered to have an important function in gene regulation.
Bob