I once saw a rabbit with the presenting complaint of “face twitching”, and then I gave her a drug that could have easily killed her, but instead she was cured and went home with three babies. This is the biology behind her story.
Calcium, it’s what’s for dinner.
As a kid you were encouraged to drink milk so you would build strong bones, but the flip side is that you need bones with a lot of calcium to help regulate the amount in your blood. Bones are a bit like a lending library for calcium. Need some? Pull it from the bones. Have extra? Store it in the bones for a rainy day.
Calcium is used everywhere in the body. It’s necessary for smooth muscle contraction, it affects the length of time before cardiac muscle is ready to go again, and low calcium can cause neuromuscular irritation. Name any system in the body, and calcium will somehow be important there, too.
Rabbits Are Just Tiny Horses
In many ways rabbits really are more similar to horses than dogs or cats. Prone to dying from gut issues, check. Foot issues, check. And unlike most mammals other than horses, rabbits absorb most of the calcium in their diet, and then get rid of the extra in their urine.
As you can imagine, having sludgy urine with a bunch of calcium sediment in it is not comfortable, and can lead to bladder stones. Because of this, most rabbit owners feed their rabbits grass hay, which has about a third of the calcium found in alfalfa. Not as much calcium in the food leads to less sludgy urine. It’s a win for everyone.
Except…
There are times when a rabbit might need a little extra calcium. Pregnancy and lactation are the two biggest ones. In the case of my patient, the pregnancy was an “oopsy” according to the owners, though I would argue that if you have intact rabbits, they will find a way, as indeed these rabbits had. (Rabbits also get a lot of uterine cancer, so just spay your pet rabbits, okay?) The owners hadn’t planned on breeding the rabbits, and weren’t really prepared for it, and all their rabbits were eating grass hay.
Everything was going well until the rabbit reached the end of gestation and started producing milk in preparation for the babies that would soon be there. The calcium balance was already teetering on the edge because the fetuses were using calcium for their bones, and suddenly the calcium level in doe’s blood wasn’t high enough. That caused two immediate problems in this patient:
- Because the uterus is made up of smooth muscle, and smooth muscle requires calcium to work, the rabbit stopped having contractions.
- Low calcium caused neuromuscular excitation. In dogs you often see that as a stiff gait, but that’s a little harder to see in a rabbit. What we did see were spasms on one side of the rabbit’s face.
(It could have been worse. In birds with low calcium, often the first thing the owner notices is the bird having a full-blown seizure. That’s often fatal.)
Anyhow, we were pretty sure of the cause of this rabbit’s problems, so we knew the solution: give the rabbit calcium. That’s easy enough. If her symptoms had been less severe, we could have just corrected everything with diet changes, but those kits were ready to be born and couldn’t wait. So IV calcium was called for. Pump her full of calcium then pop her in a cage and wait for the babies, right?
Hold Up There
This is another one of those cases where drugs affect different muscle types in different ways. If there’s too much calcium in the blood, cardiac muscle takes longer to repolarize, which is a fancy way of saying the heart slows down. If you give calcium too quickly, you can literally stop the heart.
So as much as it would have been nice to give the rabbit a big dose of calcium and then let her relax in a quiet place to give birth, I had to stand there for fifteen minutes with a syringe in my hand, monitoring her heart rate. Naturally the minute her face stopped twitching, a kit popped out the back end.
(I had been hoping she wasn’t actively in labor yet because stressed rabbits can eat their young, and I’m not sure what is more stressful than an exam table in a vet hospital with a resident staring at you. Luckily this rabbit was used to people.)
In this case the doe and all her kits went home healthy, and that doesn’t happen all that often in avian and exotics practice.
Links
Want to know more? Try some of these resources:
- https://www.harcourt-brown.co.uk/articles/free-food-for-rabbits/calcium-and-rabbit-food
- http://www.pethealthnetwork.com/dog-health/dog-diseases-conditions-a-z/hypocalcemia-dogs
- https://www.ncbi.nlm.nih.gov/books/NBK279022/
- https://myemail.constantcontact.com/Don-t-give-IV-calcium-to-a-standing-cow.html?soid=1105909906452&aid=ipnV4kiUjwU
- https://med.libretexts.org/Bookshelves/Anatomy_and_Physiology/Book%3A_Anatomy_and_Physiology_(Boundless)/17%3A_Cardiovascular_System%3A_The_Heart/17.3%3A_Cardiac_Muscle_Tissue/17.3A%3A_Mechanism_and_Contraction_Events_of_Cardiac_Muscle_Fibers
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