Kidney disease is not uncommon in older rats especially males and is thought to be the third most common cause of death after respiratory illness and tumours. It accounts for many deaths where the rats just gradually decline and die for no apparent reason. Treatment in humans is dialysis and transplantation, which are obviously unavailable to our small pets, but diet also plays a large role in maintaining balanced blood chemistry and delaying the need to start dialysis. The following treatments should be considered palliative; they should improve quality of life and possibly slow down the progression of the disease process. But there is no cure.
Much of the malaise that accompanies kidney failure is due to high levels of toxins circulating in the blood. This is called uraemia. Protein is broken down in the liver and this process produces waste products (particularly urea) which are then excreted by the kidneys. When the kidneys are failing the urea is able to build up in the blood.
Symptoms of uraemia are:
- loss of appetite
- fluid retention
- encephalopathy (toxicity of the brain causing confusion/clumsiness and eventually coma leading to death)
With this in mind the best sources of protein are egg and fish, then chicken and finally the red meats. Of the vegetable protein sources, soya is the most useful.
It has traditionally been the case that when a rat is elderly and 'failing' we increase the protein load he has to deal with by feeding foods such as EMP, porridge, scrambled egg etc. I would suggest that we might consider an alternative approach. In the absence of other obvious symptoms it is wise to assume that all elderly rats in decline have a degree of kidney damage. For many this will be serious enough to be the cause of their decline. For the rest, feeding a 'kidney-friendly' diet will only serve to protect their kidneys from further damage.
As well as considering the amount and quality of the protein given, the other main factor affecting the progression of the disease is phosphorus intake. When the kidneys begin to fail phosphorus (which is a component of all foods) isn't excreted as efficiently and blood levels begin to rise. Calcium and phosphorus are closely linked, and as the phosphorus level rises calcium is pulled out of the bones. This not only weakens the bones, but increases the levels circulating in the blood. These minerals can then be deposited in soft tissue around the body. They then cause inflammation and discomfort. Where they are deposited in the kidneys they will serve to increase the rate at which the kidneys fail.
Reducing dietary intake of phosphorus is critical to slowing the progression of the disease process. This can be done in two ways: avoiding high phosphorus foods in the diet and giving phosphate binders along with food. The old fashioned medications (calcium carbonate) that we take as antacids, are good phosphate binders and are very safe.
The kidney friendly diet
Since kidney deterioration is common in elderly rats it is probably sensible to begin to make the diet more kidney friendly for rats once they reach about 18 months of age. This can be done easily by selecting a dry mix that is based on lower phosphorus cereals like barley, corn, rice, millet and buckwheat, while in the main avoiding unprocessed wheat, rye and spelt. Almost all processing, but especially that which creates a "white" version of the grain, significantly reduces phosphorus levels.
Protein sources can be soya, egg (such as presciption diet for kidney support - Hills K/D, or egg yolk biscuit) or a good quality fish kibble.
Straight grain mixes are the easiest to change to be kidney friendly - and a ready made mix is available from Rat Rations - number 8 complete mix for kidney support.
Example of a dry mix based on Harrison's Banana Rabbit brunch:
- Harrison's Banana Rabbit brunch (approx 40% by volume with some banana removed*)
- Hills Prescription Diet K/D Canine (approx 20% by volume). This is a dog kibble designed to support chronic renal failure in dogs. It is low phosphorus and restricted protein (primarily egg based). It is a useful source of copper in this diet too (14mg/kg). It has a high fat content, but I feel the other benefits outweigh this at this time in a rat's life. Much of the rest of the dry mix is very low fat. A 2kg bag cost about £10 but will last you a good while. If you have ethical problems feeding a product from this manufacturer you can substitute with a daily mix of cooked rice/seaweed powder/raw beaten egg/garlic/crushed copper tablet - all cooked for a minute until solid in the microwave.
- white pasta spirals - uncooked/egg noodles - uncooked (together approx 10% by volume). Noodles are a lower phosphorus alternative to pasta, but I include them in roughly equal amounts. Do not substitute with all pasta.
- Broken low salt unflavoured rice/corn cakes or mixed puffed whole grains (approx 15% by volume).
- Bite-sized shredded wheat/corn flakes or similar (15% by volume). Do not substitute other cereals unless you check phosphorus levels first. Shredded wheat seems to be one of the few low-ish phosphorus whole grain wheat based cereals. Oats are high in phosphorus, as is bran.
This dry mix makes up 60 to 90% of their daily food.
As well as this I feed Lite Nature Diet or an eggy rice mixture with flax oil and supplements.
- flax oil (shown to slow progression of disease)
- rushed Rennie tablets or Ipakitine (binds phosphate in the diet) - only needed if treating actual kidney failure.
- 1 crushed vitamin B complex tablet (improves associated anaemia and may help slow spinal degeneration)
- Daily Rat 3 (copper, Vitamin D and Calcium mix).
Foods that are particularly high in phosphorus that should be avoided are whole-wheat, bran, oats, dairy (soya products are better) and nuts.
Adequate quantities of fresh water should be available at all times.
Author: Alison Campbell