Deformity in Kits

Question
QUESTION: I have just had two litters from different mums and dads and in one litter there were 3 kits and 1 had an exposed brain or no covering over the brain area, the rest of the kit was normal and the others were normal to, the other litter there was only 1 kit and it had an exposed brain with the brain or part of it missing. I have been breeding for a few years and have not had this before, my rabbits are all pedigree and registered. Can you help? They are fed on hay and pellets and carrots and the parents were not closely related. Thanks.

ANSWER: Dear Faye,

The deformity you describe is consistent with a neural tube defect, such as spina bifida or acrania (lack of a cranium) seen in humans (and other mammals).  In most cases, this condition is not genetic, but rather a result of teratogenesis:  exposure to an environmental toxin that interferes with normal rolling and closing of the neural tube during embryogenesis (formation of the embryo).  This happens very early in gestation, possibly before the bunnies were even obviously pregnant.

Agents known to cause this type of defect in humans include Vitamin A and salicylate (the active ingredient in aspirin), which is why pregnant women are not supposed to take vitamin supplements, acne remedies such as Retin-A, or even aspirin without consulting their obstetrician.

Teratogens vary in their effects across species, so whatever affected the development of these babies might remain a mystery.  Any pesticides around the rabbits?  New dietary supplements?  Are they chewing on something in the cage that might have some toxin?  Paint?

There is also the possibility that this was either truly genetic, or else an idiosyncratic developmental error that wasn't due to an outside agent.  But since 30% of the kits from two different litters had this problem, that seems less likely, especially if the parents are not related.

So now the job becomes to identify what the mother bunnies might have been exposed to very early in pregnancy that might be responsible.  Unfortunately, I'm not sure anyone knows which teratogens might cause neural tube defects in rabbits.  

I'm sorry about this sad outcome.  But please also see:

www.bio.miami.edu/hare/breeding.html

I hope this helps.

Dana

---------- FOLLOW-UP ----------

QUESTION: Thank you, the only thing different in the bunnies environment or diet is that I have been feeding only pellets and hay and no carrots of late which I was giving to them every few days and I have had a new batch of hay which in places was not as dry as it could have been when bailed so saw a little mould which I pulled out but wonder if that could be it or maybe something that was sprayed on the grass prior to bailing. What do you think?

Answer
Dear Faye,

I just sent an addendum to the previous question that you might have read by now.  It has a citation for an article indicating that rabbits are unusually sensitive, teratogenically, to some forms of Vitamin-A related compounds.  So I wonder if the pellets are very high in vitamin additives?

Something sprayed on the grass might also have this effect.  And if rabbit ate moldy hay, all bets are off, since many types of fungi produce mycotoxins that can have teratogenic effects.

So if you try remedying those problems, all of your bunnies will be healthier in general.

Dana