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Diabetes is very rare in pet rats: most of the information in this section was obtained from someone who was working with a laboratory strain of diabetic rats used to assay insulin.
However, the diabetes which sometimes occurs naturally in fancy rats seems to be identical to that seen in the lab. strain: and precisely because the condition is rare not many people know how to treat it, so it is worth writing down the details.
The onset of the disease is generally at around 90 days. It is characterized by excessive drinking and urination and an unusually fine, glossy coat.
If untreated, the condition is fatal within a few months. With proper treatment, however, the lab. strain are healthy up to 18 months, at which point they begin to deteriorate: since they are an inbred strain it is not clear whether this comparatively short lifespan is due to the diabetes or to some unrelated factor.
Treatment consists of the administration of insulin by subcutaneous injection once a day.
The initial dosage for a 90-day old buck weighing around 300 grams is 6 units of a .5ml low-dosage insulin syringe or 5 units for a 250 gram doe (i.e. around 1 unit per 50 grams body weight) using U40-strength insulin.
A "unit" in this context is a measurement peculiar to diabetics, and is equal to 0.01ml. Since insulin-syringes come marked out in units it is simpler to give the measurements that way: but if you are using another type of syringe remember that the dose is 0.01ml per 50 grams weight.
Unfortunately U40 insulin is very difficult to obtain, so it will probably be necessary for your vet to buy U100-strength insulin and dilute it to U40-strength. It is not advisable to use the stronger insulin undiluted and simply reduce the dose in proportion, as the amounts involved are very small and the exact dose is important.
If the rat who is being treated starts to seem unwell again the dosage may need to be increased, and to assess this a blood test must be performed. A gadget used by human diabetics and called a Reflolux should be used for this: find a sympathetic diabetic who will let you borrow theirs, or ask a local diabetic support group if they have any old ones that they no longer use.
The test involves smearing a drop of blood on a strip impregnated with chemicals. To draw the blood - "just a pinprick" - my informant makes a small nick at the end of the tail with a scalpel, and he tells me that this is so painless that "they don't even look round" (loss of sensation in the extremities is common in diabetes). According to what the blood test shows the dose can then be increased, up to a maximum of 1 unit of U40 insulin per 25 grams of weight.
If you are going to attempt to treat a diabetic rat then unless you have the good fortune to live round the corner from your vet it will be necessary for you, the patient's personal servant, to learn how to give injections. This is actually fairly easy: ask your vet to show you how.
The normal site for injections is the scruff of the neck, but some bucks have skin on their backs like boot-leather, and have to be injected in the "skirts" - the soft flap of skin between the elbow or knee and the body. Most rats don't have very sensitive skins, and react to injections very little if at all: but if the rat's shoulders become sore from repeated injections into the scruff then you can rotate the injection-site between the scruff and each of the four skirts.
My informant tells me that if a diabetic rat should happen to die in the night, so that the body is not immediately removed, the dead animal's cagemates sometimes nibble the body. Cannibalism is almost unheard of in rats, and he attributes this to the sweet smell caused by the disease, which becomes more noticeable if the body has been lying all night and has begun to heat up.