Does high protein diet cause sores and spots?
High levels of dietary protein (over around 16%) are frequently quoted as being the cause of spots and sores in rats. It is my opinion that this is almost certainly a myth and as yet I have been unable to determine the original source of the idea. I have also been unable to find a single documented piece of research that suggests this is true. On the contrary, most of the 'evidence' (various accounts of first hand experience) does seem to suggest that it is unlikely.
In Pro.Rat.a Number 133 (January/February 2003) Rachel Rodham outlines her experiences with laboratory rats in the years before they were SPF (specific pathogen free). These rats frequently had spots and sores that were always found to be due to mites. Once the colony went SPF the sores never recurred (the rats were mite free). The two colonies were fed exactly the same diet (lab blocks with a relatively high protein level of around 22%).
My own rats have a very stable diet with no large protein surges, but we still see outbreaks of sores and scabs over individual rats' chins and shoulders. I decided about 6 months ago to treat every outbreak as though it was mites. In every case the treatment given (Ivermectin applied topically) has been effective. I am increasingly inclined to agree with Ann Storey when she writes: "I am pretty convinced that most cases of spots are caused by a skin allergy (skin biopses shows this) and that this is generally due to mites."
Ann goes on to mention a number of factos that she feels may make a rat more prone to showing these symptonms. These include:
Genetic predisposition
Social standing (the 'middle' level rats in a colony)
Weak immune system
Weather changes (Spring and Autumn)
I would add that stress seems to be a major factor (most of the things Ann mentions are indeed stressors), as is illness, pregnancy and (possibly related to weaknesses in their immune systems) being a blue based rat (blue, lilac, platinum).
It is quite plausible that fur mites are endemic in the rat population, but in most cases a fat, unstressed rat will cope with these and remain symptom-free. Stressors (possibly under the influence of genetic predisposition) might then lead to symptoms. Certainly in humans the ability of the immune system to react to normal processes like inflammation is reduced under stress, hence the relationship between stress and eczema/psoriasis. It is also plausible that certain rats may respond 'through' their skin to allergies to certain foodstuffs, but this does not mean that a high protein diet leads to spots and sores.