Calcium in vegetables

[Alfreds minion]

I’ve been looking into calcium in the fresh vegetables we feed rabbits. I can only find sources (vets etcetera) that say it is NOT necessary to limit high calcium greens, at least in buns that have no history of sludge or stones. Does anyone have any links to reliable opinions that do suggest it’s something we need to limit or be concerned about?

The professional opinions do seem to be somewhat divided about the importance of dietary calcium in bladder sludge/ kidney stones etc, but no-one seems to recommend limiting high calcium fresh vegetables that I can find. Though the reasons given as to why it is not a problem vary a bit.

 Just to be clear, the calcium content of dry food as alfalfa hay and pellets (In particular alfalfa based ones) is considered an issue / problem by many of the sources I’ve been looking at.

I would appreciate any links to different opinions! My Google skills may be letting me down : ) I’d also be interested to hear if your vet advises limiting high calcium greens (especially if your bun has no problems with sludge, stones etc) OR has anyone read any journal articles etc. that support the idea that high calcium fresh greens should be limited? Thanks!

[Azerane]

While I can’t say I recall having read any actual journal articles on the matter, I have read a number of different things on it and reasonings behind certain limitations.

What limited and possibly (in)accurate information I know is this. At least for indoor rabbits who may have limited or no access to sunlight, calcium may be a larger issue than just sludge. Vitamin D aids in calcium absorption, so a lack of vitamin D and insufficient calcium greens in house rabbits could potentially lead to dental issues or brittle bones (deductive speculation on my part) due to insufficient calcium in the diet. In addition to that, without vitamin D and with a high calcium green diet, a house rabbit may have too much calcium passing through their system and ending up in the bladder because the body can’t absorb it properly. Again, more speculation.

On the other hand, I do know that a rabbit’s body is designed to excrete excess calcium through the bladder, it’s just when this calcium becomes in excess that it is an issue. I also remember reading something about rabbits being more susceptible to sludge are those that aren’t as active, or may be stuck in smaller cages. Because rather than the calcium passing evenly in the rabbit’s urine, it collects at the bottom of the bladder as it’s not being stirred up as the rabbit is hopping around and doing binkies and running etc. Can’t remember where I read that, but I remember thinking it was an interesting idea at the time.

Thirdly, I believe when talking about dietary calcium, you also need to consider high oxalic acid greens. As oxalic acid limits the uptake of certain minerals etc. and I believe actually binds to calcium. So if you’re feeding lots of high calcium greens, and lots of high oxalic acid greens, then that is potentially when crystals will be forming because the oxalic acid binds to the calcium to form them. At least that’s what I remember anyway.

All that being said, my aim for leafy greens was always to alternate days. One day would be my low oxalic acid day, the next was my low calcium day.

All that being said, you are probably correct that there isn’t a need to limit calcium unless the rabbit in question has a history of sludge. Just the same with people getting bladder stones I suppose.

Take what I’ve said with a grain of salt, I’ve read a lot, but none of it particularly recent and like you mentioned, all of it would have been general or vet based or similar websites, not actual journal articles.

[jerseygirl]

Worth a read: http://www.harcourt-brown.co.uk/articles/free-food-for-rabbits/calcium-and-rabbit-food

[Alfreds minion]

Thanks Azerane, I am impressed with your knowledge and you have said it better than I could have, even though i’ve read about it all so recently. And I’m certain to have forgotten it all by Friday.  Though there do seem to be differing views on it all, at least if I’ve understood everything correctly (and it’s certainly more than possible that I haven’t)

Dietary calcium is definitely recommended to be limited by most of the sources that I can find. It’s just that they say that the calcium in greens is not a concern. One reason given is that greens don’t have as much calcium as they seem to (simple eh?). Calcium must be calculated on a ‘dry matter basis’, but in practise the greens we feed are 70 to 85% water. Whereas alfalfa hay and pellets don’t have nearly as much water and so are a much more concentrated in their calcium content. At least that is my understanding as a total layperson : ) . There is a pdf article that I have misplaced that explains it well, and Frances Harcourt-Brown explains it in this article – 
https://www.harcourt-brown.co.uk/ar…abbit-food
She also mentions the role of vitamin D, and if you follow the link to the diet sheet at the bottom of the page ( for rabbits with urinary tract disease) she does recommend avoiding greens high in oxalate, as it may ‘play a part in the development of stones in the urinary tract and is best avoided in rabbits with urinary tract disease’ but does not recommend limiting high calcium greens.
Frances Harcourt-Brown seems to be considered an expert in this, I think she’s written a book on it, or some similar subject? She seems to place emphasis on the importance of exercise (as you mention) in the prevention of stones and sludge.

I am sure it does absolutely no harm at all to limit high calcium greens; perhaps it is even a good precautionary measure, and it sounds like you’ve got a good system. It would just be awfully nice if we didn’t have to worry about taking the calcium content into account. Occasionally folks do seem intimidated about feeding their bun vegetables. But really I’m just trying to guage for myself how much I need to be aware of it when I feed Alfred.

[Alfreds minion]

Thanks Jerseygirl, I should’ve refreshed the page before I posted 

The other article I mentioned that has a good explanation of what I was trying to explain is a pdf called CALCIUM METABOLISM IN RABBITS by Leah Postman DVM.

This is the bit I mean –
  ‘The other potentially significant source of calcium in rabbits’ diets is fresh greens. Although many people
worry about the greens noted for high calcium content — kale, spinach, collards — I do not. All fresh
greens are about 70% to 85% water, which greatly dilutes all nutrients. To eliminate the potential to
misrepresent nutrient content due to variability in water content, it is essential to compare calcium
content on a dry matter basis, which is how the nutrient requirements are expressed on labels and in
tables. For example, kale, which many recommend avoiding by virtue of its calcium content, has 1.6%
calcium on a dry weight basis. In other words, dehydrated kale has roughly three times the NRC
recommended calcium content. However, the fresh bunch of kale is mostly water, so the calcium
content drops dramatically, to 0.24% when fed fresh. If you were to feed a medium-sized (5 pound)
bunny 1/4 cup (about 60 grams) of a pellet meeting NRC recommendations, he would consume about
0.30 grams of calcium. To obtain a similar quantity of calcium from kale, the bun would have to eat over
4 ounces (130 grams) of kale. That is a sizable pile of kale — about as much as you could stuff in a half
gallon milk carton. Similarly, dandelion greens, have a calcium level of 1.6% on a dry matter basis. But
since our bunnies eat them fresh, they are only getting 0.20% calcium. Again, we see that even for
greens with a relatively high calcium content, the calcium level of the leaves the bun is munching is
actually quite low.’

[Luna]

Luna does not have a history of sludge or stones, and when I asked my vet for a list of suggested veggies she warned not to feed Luna solely the high calcium veggies all the time. Oddly, though her vet has been treating exotics for 15 years and I trust her completely, she was perplexed by my questioning of oxalic acids. It could be a learning culture thing? (ie. vet teachings in U.S. vs. U.K/Australia) Not saying teachings in one country is better than the other!

[vanessa]

I’m not afraid of feeding my bunnies high-calcium veggies for the exact reason Azerane said. I did limit them because of the calorie content, as Guin is a BBB (Big Beautiful Bunny). I do think though that since limiting the kale, I see less chalky pee from her. she is the only one who has exhibited chalky pee.

[vanessa]

I don’t limit dandelion. It’s just wayyy too healthy 🙂 I normally have a lot of dandelion growing in my garden over winter, as well as chick weed. But this winter didn’t get that cold, and we barely had any snow, so no dandelion or chickweed to pick. The dandelion will come back in spring though – it seems to have 3 growing cycles a year. Winter, spring, and fall.

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