There's been a lot about that so I will trust people to actually look
up most of the reputable resources out there, but the confusion sadly
remains.

Animals who are descended from others that regularly got livers are
adapted to deal with decent levels of A which is in high amounts in
liver. Can they get too much? Sure, but it takes a lot to do that with
them, unlike with humans.

On the other hand, animals which had ancestors with mainly crepuscular
activity (dawn and dusk) or nocturnal activity, and especially those
whose ancestors were also burrow dwelling have a harder time with
vitamin D, unlike humans whose ancestors had a lot of sun exposure.

So, ferrets are kind of the opposite of us for those two vitamins and
those differences confuse some people.

First D:

What happens when a type of animal, like ferrets and dogs, which
are not geared to getting much D do get too much D? They develop
hypercalcemia with calcium deposits in organs, especially in the
kidneys and heart. In fact, there were multiple discussions about that
recently. Obviously, they do need some, but not in high levels since
they get overdosed quite easily.

There are a number of reputable refs on that. I don't have time to find
many but you can start with things like this and those who were at the
symposium in PA will recall Dr. Tom Willard mentioning the concern for
ferrets, too, in discussions:

>J Small Anim Pract. 2005 Jul;46(7):334-8.
>
>Hypercalcaemia in two dogs caused by excessive dietary supplementation
>of vitamin D.
>
>Mellanby RJ, Mee AP, Berry JL, Herrtage ME.
>
>Queen's Veterinary School Hospital, University of Cambridge, Madingley
>Road, Cambridge CB3 0ES.
>
>A three-year-old Border collie was presented with a two-week history
>of lethargy, stiff gait, polydipsia and polyuria. Biochemical analysis
>revealed hypercalcaemia. Serum concentrations of 25-hydroxyvitamin D
>(25[OH]D) and 1,25-dihydroxyvitamin D (1,25[OH]2D) were markedly
>elevated and parathyroid hormone was undetectable. Subsequent analysis
>of the dog's diet revealed that the food contained excessive amounts
>of vitamin D. The hypercalcaemia resolved following treatment with
>bisphosphonates and dietary change. Hypervitaminosis D was diagnosed
>in a second unrelated dog, which had been fed the same brand of dog
>food as case 1. The dog was also hypercalcaemic and had markedly
>elevated serum concentrations of 25(OH)D and 1,25(OH)2D.
>Hypervitaminosis D in dogs has been reported to occur secondarily to
>ingestion of either rodenticides containing cholecalciferol or
>antipsoriatic ointments that contain vitamin D analogues.
>Hypervitaminosis D has also been reported following the treatment of
>hypoparathyroidism. To the authors' knowledge, this is the first
>report of hypervitaminosis D in dogs following the accidental over
>supplementation of a commercial diet with vitamin D. While the
>benefits of adequate dietary vitamin D are well established in dogs,
>the potential deleterious effects of over supplementation of vitamin D
>should also be acknowledged.

See, too:

http://news.vin.com/VINNews.aspx?articleId=16727

The MSU Veterinary School periodic magazine which went into that in
detail is currently not coming up. Links were given when it first
appeared, and perhaps those who missed it then will be lucky enough
to have it reappear in the future.

Okay, now moving from D to A:

What happens when a type of animal, like ferrets, who are geared to get
a good amount of A don't get enough A? Well, among other things they
appear to have decreased resistance to some serious diseased like
canine distemper. There are also increased problems with diarrhea,
cataracts, behavioral alternation, and more.

>1. J Nutr. 2007 Aug;137(8):1916-22.
>
>Disease manifestations of canine distemper virus infection in ferrets
>are modulated by vitamin A status.
>
>Rodeheffer C, von Messling V, Milot S, Lepine F, Manges AR, Ward BJ.
>
>McGill University Health Centre Research Institute, Faculty of
>Medicine, Division of Infectious Diseases, Montreal General Hospital,
>Montreal, QC, Canada.
>
>The measles virus (MV) causes half a million childhood deaths
>annually. Vitamin A supplements significantly reduce
>measles-associated mortality and morbidity. The mechanisms whereby
>vitamin A acts against MV are not understood and currently there is no
>satisfactory small animal model for MV infection. We report on the
>development of a ferret model to study antiviral activity of vitamin A
>against canine distemper virus (CDV). CDV is closely related to MV at
>the molecular level and distemper in ferrets mimics measles in humans.
>We infected vitamin A-replete (control) and vitamin A-depleted ferrets
>with CDV and assessed the ability of high-dose vitamin A supplements
>to influence CDV disease. In control ferrets, CDV infection caused
>fever, rash, conjunctivitis, cough, coryza, and diarrhea. In contrast,
>control ferrets that were given 30 mg of vitamin A did not develop
>typical distemper after infection and exhibited only a mild rash. The
>supplement did not negatively affect ferret health and resulted in a
>100% increase in serum and liver vitamin A concentrations. We also
>found that profound vitamin A deficiency is inducible in ferrets and
>can be rapidly reversed upon high-dose vitamin A supplementation.
>Vitamin A deficiency caused anorexia, diarrhea, cataracts, behavioral
>abnormalities, and ultimately death, with or without CDV infection.
>All ferrets that received vitamin A supplements, however, recovered
>uneventfully from CDV infection. These results replicate many aspects
>of the observations of vitamin A therapy in humans with measles and
>suggest that CDV infection in ferrets is an appropriate model for the
>study of the antiviral mechanism of vitamin A.

Full article for free:  

http://jn.nutrition.org/content/137/8/1916.long

Fish oil is a good source of omega 3 fatty acids which are useful for
kidney health in ferrets, but cod liver oil -- as opposed to "fish oil"
which is from entire fish instead of just livers -- is very high in A,
so unless a ferret is fighting canine distemper or in a risk situation
for CDV that is best given somewhat sparingly just to be safest, while
remembering that ferrets do cope with higher A levels better than
people do, and appear to need higher A levels proportionate to size
than we do.

BTW, unlike humans, ferrets and a number of other members of Carnivora
have difficulty converting some vegetable precursors of vitamin A into
vitamin A.

Sukie (not a vet)

Recommended ferret health links:
http://pets.groups.yahoo.com/group/ferrethealth/
http://ferrethealth.org/archive/
http://www.afip.org/ferrets/index.html
http://www.miamiferret.org/
http://www.ferrethealth.msu.edu/
http://www.ferretcongress.org/
http://www.trifl.org/index.shtml
http://homepage.mac.com/sukie/sukiesferretlinks.html
all ferret topics:
http://listserv.ferretmailinglist.org/archives/ferret-search.html

"All hail the procrastinators for they shall rule the world tomorrow."
(2010, Steve Crandall)
On change for its own sake: "You can go really fast if you just jump
off the cliff." (2010, Steve Crandall)

[Posted in FML 7223]