Low Calcium Diet for Rabbits
Calcium is essential for rabbits to maintain healthy bones and teeth, but the special way rabbits process it means that some rabbits encounter urinary tract problems if their diet is too high in calcium. If your rabbit suffers from stones or bladder sludge you may need to adjust their diet to reduce their calcium intake to help control the problem.
Remember: you should always work with your vet to resolve health issues, so if you are unsure about what is an appropriate diet for your individual rabbit please discusses it with your vet. Introducing new foods should always b e done gradually to allow your rabbit's gut to adjust.
You can tailor this article to give portion sizes and calcium content according to the size of your rabbit, to do that please enter your rabbit's weight here:
Keep in mind these are approximate calculations and individual's calcium requirements vary, so figures are a guide rather than something you should follow rigidly. It's likely to be less accurate for extremely small or large rabbits as their requirements may not be proportionate.
- How Rabbits Process Calcium
- How much calcium should rabbits have
- Calculating Calcium Content
- Components of a Low-Calcium Diet
How Rabbit's Process Calcium
In most mammals any calcium needed by the body is absorbed as food passes through the digestive tract and any leftover calcium continues on to be excreted as waste (poop). In rabbits, all the calcium is absorbed through the digestive tract and then what isn't needed is later excreted via the kidneys in the urine.
It's normal for healthy rabbits to have some calcium in their urine, which can give it a slightly cloudy appearance and may leave a chalky residue when it dries (this can be removed by cleaning with white vinegar). However, in some rabbits the calcium binds together to form a stone, which may need surgical removal, or creates sludgy silt in the bottom of the bladder that is difficult to pass and makes the urine milky coloured and gritty textured. This can result in damage to the bladder and frequent urinary tract infections.
How much calcium should rabbits have?
If your rabbit has been diagnosed with bladder sludge or a related urinary tract issue your vet may have advised a lower calcium diet. The goal of a low calcium diet isn't to remove calcium completely; calcium is necessary for a range of body functions including normal rabbit teeth growth. Instead the aim is to reduce calcium to only what it used by the body, cutting out excess calcium that's disposed of via the urinary tract.
The RDA (recommended daily amount) of calcium for an adult pet rabbit is approximately 200mg per 1kg body weight, so 500mg for a 2.5kg rabbit. Most rabbits with calcium issues are eating a diet that provides more than this, so when we say low calcium, often what we mean is just cutting back to no more than the recommended amount.
One of the first things you might like to do is work out how much calcium your rabbit currently has in their diet and compare this to the RDA. An individual rabbit's calcium requirement varies, so this will give you a base line to work from.
Calculating Calcium Content
Working out how much calcium is in different foods is not as simple as it seems, and confusion over how to calculate calcium content means that some foods have been unfairly blacklisted for appearing too high in calcium.
Calcium content information is often given as a percentage of dry matter. Dry matter is what is left when the water is removed. All foods, including 'dry' rabbit foods like pellets have some water content. Rabbit pellets have a low water content (10%) as does hay (13%), where as fresh foods have high water content, such as spring greens (85%) or grass (80%). When calcium is given as a percentage of dry matter, foods with lots of water can sound high in calcium when really they aren't. To work out the actual amount of calcium in a portion, we need to factor in the weight of the food when all the water is removed.
The formula the calculator above uses is:
((Weight of Food x % Dry Matter) x % Calcium) x 1000 = mg of calcium
Components of a low-calcium diet
A healthy diet for a rabbit with urinary tract issues has the same components as one for the average rabbit - that is lots of grass/hay, some fresh vegetables or other plants, and a small amount of commercial pellets. For rabbits with urinary tract issues we just need to give a little more attention to the proportion of these foods to ensure we end up with the right amount of calcium and substitute a few ingredients that are particularly high in calcium.
Next, let's look at each food group in a little more detail.
Hay / Grass
Rabbits evolved to eat grass so, unsurprisingly; it provides the most suitable balance of nutrients, including calcium, to meet their needs. Like all rabbits, those on a low calcium diet should eat plenty of grass-hay or fresh grass. Any variety of grass is fine, including timothy, meadow and orchard. They all provide a calcium content of between 0.3-0.5% of dry matter, depending on the variety and even where it grew and when it was cut. Alfalfa is sometimes fed as a hay substitute, particularly for young rabbits, unlike grass-hays it has high calcium content (1.3%) so should be avoided in rabbits with calcium related urinary tract issues.
Remember, both grass and hay (dried grass) have the same amount of calcium blade for blade; it's just fresh grass also has lots of water which makes it heavier. The benefit of fresh grass over hay is its water content (you'll learn about the importance of water below). So where possible replace some or all of your rabbits hay with fresh grass (make the switch gradually). Fresh grass is just as good as hay for rabbits, including providing adequate tooth wear. You can find out more about feeding hay and grass here.
A 2.5kg rabbit could eat 500g of grass or 115g hay (dried grass) before reaching their 500mg RDA of calcium. However, in general a 2.5kg rabbit fed a mixed diet (including pellets and/or greens) is more likely to eat around (330g of grass/75g hay - providing 330mg of calcium. Although the actual amount your rabbit will eat depends on things like breed, activity level, age and the other foods they have access to.
To calculate your rabbit's daily grass/hay intake weigh what you initially provide and then weigh what is left 24 hours later. Never restrict your rabbit's access to grass/hay - they should be encouraged to eat as much as they want. If you need to reduce calcium it should always be done by reducing the amount of other components of the diet, not grass.
Low Calcium Dry Food
Dry food is very high in calcium; it accounts for most of the excess calcium in rabbit's diets. There are two steps to resolve this; the first is to reduce the amount of dry food you feed and the second is to pick a brand of dry food that has less calcium to start with.
The most frequently quoted daily dry food portion for a rabbit is 25g of food per 1kg your rabbit weighs, i.e. a 2.5kg rabbit should have a maximum of 63g per day. The average calcium content of rabbit pellets is around 0.9%; using the calculator above, this works out at 510mg of calcium for a 63g portion. This means your rabbit would use up all of their calcium allowance before we've factored in hay or greens! The reason for this is pellet rations and calcium values originate from commercial breeding practices where pellets were used as a 'complete feed' and not complimentary to hay - they were designed for growing rabbits quickly and cheaply rather than long term health.
The best way to reduce the amount of calcium in your rabbit's diet is to replace some of their dry food with extra hay and/or greens. By doing this, the amount of dry food can be reduced dramatically e.g. 10g per 1kg of weight per day (25g total for a 2.5kg rabbit) which would give a slightly more reasonable 203mg of calcium per day.
We can reduce the calcium intake further by choosing a brand of dry food that is lower than average in calcium. In the dry food comparison chart here you'll see some brands have half as much calcium as others (closer to 0.45%), for example VetCarePlus Urinary Tract Health Formula, which is specifically designed for rabbits with calcium issues. This reduces the calcium content your rabbit's 25g pellet ration to 101mg, a quarter of our original total.
Now when we add the calcium from grass/hay (330mg) and pellets (101mg) we have 431mg, leaving 69mg of your rabbit's RDA still left over for fresh foods.
Low Calcium Vegetables / Plants
Vegetables and plants vary a lot in calcium, for example dandelion has a calcium content of 1.34% and carrot 0.28%. However, a chunk of carrot is much heavier than a dandelion leaf so it's also important to factor in portion size - when you do the calcium values often even out.
Calcium values in vegetables can also seem high in comparison to dry foods, as they contain a lot of water, for example kale is considered a high calcium vegetable at 0.98% around the same value as regular pellets (0.9%). However, whereas a portion of regular dry food (63g) contains 510mg of calcium, 63g of kale (a third of a supermarket bag) only contains 95mg of calcium because it's mainly water. This is why replacing some of the dry food with fresh foods helps lower calcium values.
Often low-calcium diets put a lot of emphasis on the calcium level of vegetables, but it's not necessary to exclude any completely from a low calcium diet. The key is to feed a wide variety of types to average out the calcium intake and use them to replace dry food, which is a much worse culprit when it comes to high calcium. Try to feed at least 3-5 different vegetables a day and not the same ones every day.
Here is a chart showing the calcium content based on weight and portion size:
|DM%||Ca%||Ca/100g||Portion||Portion (g)||Ca in Portion|
|Sweet pepper*||6%||0.17%||10mg||1 slice||11g||1mg|
|Cabbage||8%||0.50%||40mg||1/2 large leaf||16g||6mg|
|Romaine/Cos Lettuce||5%||0.66%||33mg||1 leaf||28g||9mg|
|Water Cress||5%||2.40%||120mg||1/6 packet||12g||14mg|
|Chinese Cabbage (Pak/Bok Choy)||5%||2.10%||105mg||1/4 head||25g||26mg|
|Kale||16%||0.94%||150mg||1/10 of packet||20g||30mg|
|Spring Greens / Collard Greens||10%||2.32%||232mg||1/10 of packet||24g||56mg|
Notes: The majority of DM/Ca values are from the: US National Nutrient Database. For sizes: assumes 12 slices per apple/pepper; packet refers to standard supermarket bagged veggies; a head is the the whole unchopped veggie; florets are the peices you get when you chop up a head of broccoli etc. *Friuts/root veggies - feed sparingly as high in sugar!
If you remember we had 69mg of calcium left over from the 500mg RDA to use for fresh foods, once we'd factored in the calcium from grass/hay (330mg) and pellets (101mg). So mix and match the options above until you end up with a total Calcium in Portions around that figure, for example:
- 1" piece carrot (4mg)
- 1-2 florets of broccoli (10mg)
- 2 romaine lettuce leaves (18mg)
- 1/4 chicory (22mg)
- 1/6 bag of watercress (14mg)
The final issue we need to look at is water. There are two ways water plays a role in diet for rabbits with bladder sludge and urinary tract issues - your rabbit's overall water intake and its effect on the formation of bladder sludge and water as a potential source of calcium.
A high water intake helps dilute the urine and encourages your rabbit to empty their bladder frequently helping to prevent build up of sludge. A rabbit will consume 10-15% of their body weight in water per day, i.e. a 2.5kg rabbit would need about 250-375ml of water per day. Both water in the food they eat and water they drink from a bottle or bowl counts towards this total.
The best way of maximising water intake is to feed fresh foods, as these have high water content which contributes to rabbit's overall water intake. This means replacing some or all hay (dried grass) with fresh grass and replacing some of the pellet ration with fresh vegetables and other plants. It's much more natural way for rabbits to hydrate; in the wild their water needs would be met from eating fresh grass/plants rather than drinking water. Meeting their water requirement this way also means their water intake is always proportional to their food (and calcium) intake.
Rabbits should always have fresh water available, but if your rabbit eats mainly dry foods you will need to put extra emphasis on encouraging drinking water to make up the difference. Most rabbits will drink more if provided with a bowl, rather than a sippy bottle. If your rabbit soils their normal bowl, consider a coop cup which attached to the side of a cage. A small amount of juice e.g. apple or cranberry can be added to the water to make it sweet and more tempting, although you will need to refresh the water more frequently to keep it hygienic.
Calcium Content of Water
Drinking water has calcium in it, which means a rabbit eating foods low in water content e.g. hay and pellets, and obtaining their water requirement through tap water may be taking in extra calcium.
The amount of calcium in tap water varies greatly depending on whether you live in a 'hard' or 'soft' water area. In soft water areas the amount of calcium in tap water is negligible (about 15mg per litre), but in hard water areas in the UK there can be up to 120mg of calcium per 1 litre of water. That means a rabbit drinking 375ml would receive an extra 45mg of calcium (9% of their RDA).
Your tap water supplier should be able to tell you what the calcium level is in your water and, if it is very high, you may want to consider using bottled water with a low calcium level for your rabbit. In the UK you can view your calcium levels on your water supplier's website, if you aren't sure who that is check your bill or the water suppliers map here.
Different brands of bottled water have different calcium levels so check the values in the nutritional analysis on the bottle. Low calcium brands include:
|Bottled Water||mg/litre||mg in 375ml|
|Volvic Natural Mineral Water||12mg||5mg|
|Aqua Pura Still Water||14mg||5mg|
|Deeside natural mineral still water||4mg||2mg|
|Fiji Natural Mineral Water||18mg||7mg|
|Voss Still Artesian Water||5mg||2mg|
Remember: Calcium content of water is only an issue if you have hard tap water (high in calcium) and your rabbit drinks a lot of it (usually because they eat mainly dry foods with low water content).
There is a lot of information in this article, but in short feed as much hay or grass as your rabbit will eat, as this provides the healthiest balance of calcium. Reduce the amount of pellets to a maximum of 25g for a 2.5kg rabbit and choose a brand low in calcium. Feed a wide variety of fresh foods to even out high and low calcium levels. Try to maximise your rabbit's water intake by feeding fresh grass and fresh veggies, and, if you live in a hard water area, consider swapping to bottled water. Finally, remember to make any changes to your rabbit's diet gradually to allow their gut to adjust to the new foods.