Vitamin D and the rat
Dietary sources of vitamin D are limited, namely eggs, oily fish and liver, plus a number of fortified foods which occasionally include some breakfast cereals. This vitamin is added to all commercially prepared rat and rabbit mixes. There is no vitamin D in straight grains, seeds or vegetables and it is likely that rats fed on straight grain based, vegetarian and vegan mixes will need supplementation. A rat’s requirement for vitamin D is equivalent to 1,000 IU/kg feed. Assuming an individual’s intake to be between 20 and 30 grams per day this equates to 20 to 30 IU (0.5 to 0.75 micrograms) daily. Salmon flesh oil and cod liver oil are rich sources of vitamin D, but both naturally contain high levels of vitamin A as well.
In terms of international units the ratio of vitamin A to vitamin D required by rats is approximately 2.5:1, while for humans it is approximately 10:1, meaning that rats require proportionately less vitamin A in their diet. Presumably this is because humans manufacture a significant amount of vitamin D from exposure to sunlight, while our rats do not.
In salmon oil the ratio is about 6:1 and in cod liver oil and most human supplements, around 10:1. Because of this vitamin A toxicity is a possibility when usingsupplements, (problems begin to occur in humans at around twice the recommended dietary allowance of vitamin A), and it might be preferable to look for products that contain only vitamin D, to bring the ratio into a more favourable balance for our rats. The affects of vitamin A toxicity include loss of body weight, weakened bones and toxicity of the liver and kidneys, causing damage and disturbed function. Vitamin D toxicity only occurs at many times the recommended daily intake, and is very unlikely with intermittent supplementation.
Sources of vitamin D
To provide the average rat with its daily requirement for vitamin D, the following quantities of foods would be needed:
eggs - one and a half daily per rat, or
mackerel - 8g, or
salmon flesh - 3g, or
beef liver - 50g
It’s easy to see how a rat can easily become depleted if vitamin D is not supplemented!
Pros and cons of various methods of supplementation
Fish flesh oil - these oils tend to have variable amounts of vitamin D and A in them, depending on quality and source. Salmon flesh has the highest naturally occurring levels of vitamin D, however, if you use salmon oil produced for the pet market you may find the manufacturers do not list vitamin content. I contacted both
Salmopet and Fish4Dogs about their salmon oil and neither could tell me how much vitamin D or A was in their product. Since neither extracts the vitamins there will be some present, but the amount is uncertain and possibly variable. An alternative is sourcing fish oil aimed at the human market; a typical fish oil capsule containing 100 IU of vitamin D per gram is useful. Each gram of oil is approximately half a millilitre, so the daily dose is about 0.15ml. However, using fish oil as the only dietary source of vitamin D will provide a rat with more than twice as much vitamin A as is needed.
Fish liver oil - the oil from fish liver is high in both vitamin D and A, and because of a rat’s proportionately lower vitamin A requirements (in comparison to a human’s) overuse of liver oils could potentially lead to vitamin A toxicity. Cod liver oils vary enormously in strength and vitamin content so you would need to check the labelling and work out a suitable dose. Some pet grade cod liver oils are not really suitable as you would need to give too much oil on a daily basis to get an adequate dose of vitamin D. For instance the Solvitax brand cod liver oil contains 200 IU per 5ml so the daily dose would be around 0.5ml (per rat), which is a lot of extra oil in the diet and would also give ten times the required amount of vitamin A.
Vitamin A extracted cod liver oil - some companies extract the vitamin A from their fish oils so that they can be used alongside multivitamin, and this provides a really useful alternative. One such product is Seven Seas high strength pure cod liver oil with vitamin D and E. If a product aimed at the human market is vitamin A extracted, there will be no vitamin A listed in the nutritional information; be sure to check the packaging. Because the Seven Seas product is high strength only a 10th of the capsule will provide the daily dose of vitamin D. The capsules contain 0.5ml oil, so a daily dose would be 0.05ml, which is a manageable amount that can be given on a little cube of whole grain bread. One capsule can be shared between 10 rats if you are mixing it into fresh food.
Liquid calcium and vitamin D supplements - these are aimed at the pet market and are water soluble preparations, that provide a readily absorbed form of calcium along with vitamin D. They are efficient supplements and shouldn’t be given every day, because regular provision of too much calcium can cause problems. These include a reduced ability to move calcium in and out of the bones, (which is how the body copes with normal periods of increased or decreased demand), kidney stones and anaemia. Using a product like Calcivet or Calciform two to three times a week is adequate, except to support lactation, when up to five times a week is more suitable. The dose of liquid Calcivet per rat is between 0.5 and 1ml over 24 hours in water, or in food, with higher dose being used for lactation and rapid growth, or where no other dietary source of vitamin D is used. If you are using it in water, try adding 1ml to approximately 50ml water for two rats at the maintenance dose, or 2ml to roughly 50ml water for two rats to support reproduction and growth. Calciform is approximately only a third of the strength of Calcivet (in terms of calcium provision), so should be given at a higher rate. Since Calciform is designed for avian use, the doses on the packaging are not appropriate for rats and doses three times higher than those given for Calcivet will need to be used to achieve the same result - that is 3ml to 50ml water for 2 rats for a maintenance dose, or 6ml to 50ml water for two rats to support growth and reproduction. This will give a relatively high dose of Vitamin D, but with intermittent dosing this is not an issue. Calcivet has a strong taste and may be rejected in plain water, so most people add it along with Dr Squiggles Daily Essentials. Calcivet can also be bought as a powder to be added to food.
Calcium and vitamin D tablets - chewable tablets are widely available and are palatable. Giving about a 10th of the daily human dose per rat, provides (in theory) the required vitamin D plus 88mg calcium and 6.66 micrograms of vitamin K. However, in this form the absorption of calcium from the gut is less efficient and as much as two thirds of the content may be lost.
Vitamin D, calcium and copper powder - produced by Rat Rations and called Daily Rat 3, this powder gives a daily dose of the three nutritients most likley to be deficient in an unsupplemented rat diet. The powder is palatable and the amount needed is small enough to easily mix into a teaspoon of yoghurt. Can be sprinkled onto any wet food. An excellent soloution.
Multivitamin and mineral supplements - example are Dr Squiggles Daily Essentials, Bio Plus and Tiny Animal Essentials, SF50 (used to be SA37), Senior Aid and Nutrical, all of which are useful in different circumstances. Daily Essentials does not contain any calcium so it is best used alongside Calcivet for greatest effect.
It should be noted that Vitamin D deficiency can lead to calcium deficiency as it is required for absorption of this mineral, but the two deficiencies don’t always occur together. Shortfall is most likely during reproduction, rapid growth and old age, when requirements are increased, but adults may become deficient if their diet is low in Vitamin D over longer periods. Signs of deficiency (regardless of calcium status) would include poor growth, weakened bones that are more prone to injury and teeth problems.
Vitamin D deficiency is thought to exacerbate a number of illnesses and may also increase the likelihood of them happening in the first place. These include cancers, autoimmune diseases, bone disease, infectious illness and heart disease. There is a demonstrated link between chronic vitamin D deficiency and shortened lifespan in male rats. Interestingly, chronic vitamin D shortage in early life is thought to be linked to an increased risk of multiple sclerosis in humans. Hind leg degeneration is caused by a similar process of de-myelination, and it is possible that lack of vitamin D might have a causative effect.
Personally, I feel that (apart from Daily Rat 3) it is unwise to rely on one source of vitamin D since most of the supplements have their own unique issues, or may not offer sufficient vitamin D without over doing other nutrients. Therefore using a variety of methods of adding it to the diet is more likely to keep a rat at optimum levels, without any detrimental effects. My own regime is not rigid, but for maintenance I give Dr Squiggles Daily Essentials and Calcivet in their water every 3rd or 4th day, Tiny Animal Essentials and calcivet powder or Daily Rat 3 at least once a week on fresh food, a dose of Seven Seas High Strength cod liver oil once a week, a small portion of mackerel once a week as part of their fresh meal and liver biscuit treats once a week. Sick and undernourished rats also get Nutrical and they, along with the very old get egg based fresh food and wet dog food, both of which contain vitamin D. Lactating does and rapidly growing kittens also get these extras, plus Insectivorous Feast and Lactol, which also have vitamin D added. Vitamin D is stored well in the body and deficiencies only tend to occur after long periods of inadequate diet.
Adapted exert from The Scuttling Gourmet, third edition, reproduced with the kind permission of author: Alison Campbell
Articles relating to feeding rats.
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