Previously, we introduced some congenital genetic disorders in rats (click here to review), and we believe you now have a deeper understanding of rat genetic diseases!
In this issue, we will be discussing another factor that is often overlooked but can significantly impact rat health — age. Get ready to learn more about the impacts of rodent age on health!
Lab rats, like most mammals, are susceptible to a variety of age-related neoplastic (tumor-causing) and non-neoplastic diseases. The types, incidence rates, and severity of these conditions can vary significantly depending on the rat population or strain, microbial status, experimental procedures, and breeding methods (including dietary restrictions, fasting, etc.).
Chronic Progressive Nephropathy (CPN) is a significant age-related renal disease in rats and is one of the most common causes of death in rats used in lifelong studies. CPN is also referred to as ‘old rat nephropathy’. CPN is progressive in nature and is more common in male rats than in female rats.
The exact pathogenic mechanism of CPN is not clear and is likely multifactorial:
(1) Strain: The incidence of CPN varies among strains, suggesting a genetic predisposition. Sprague-Dawley and F-344 strains have higher incidence rates, while Wistar and Long-Evans strains have lower rates.
(2) Gender: Gender is a determining factor in CPN development. Male rats develop CPN earlier, have a higher incidence rate, and experience more severe lesions than female rats at any specific age.
(3) Diet: Diet is a significant factor in CPN development, and it is also the most suitable way to control it through dietary management. It is now established that moderate dietary restriction significantly reduces the incidence and severity of CPN in rats of different age groups compared to ad libitum (free) feeding.
Renal calcium deposition syndrome refers to the deposition of calcium phosphate in renal tissues, also known as nephrocalcinosis. Additional factors contributing to the development of renal calcium deposition syndrome are as follows:
Urolithiasis is the presence of mineral deposits in the urine (uroliths), occasionally found in the renal pelvis and/or bladder, with the bladder being more commonly affected. The primary components of uroliths are calcium phosphate and ammonium magnesium phosphate (struvite).
Uroliths can be occasionally observed in aged rats, but if they occur in rats younger than 6 months, it typically indicates a bacterial infection, such as bladder stones often associated with ascending infection by Escherichia coli. Rats prone to urinary tract infections, such as diabetic and obese Zucker rats, are more likely to develop uroliths and may often have concurrent renal hydronephrosis.
Chronic myocardial disease is a major cause of death in aging male rats of various strains, including Sprague-Dawley, when maintained under free feeding conditions. Similar to CPN, the incidence of this disease can be significantly reduced through moderate dietary restriction, such as reducing calorie intake by 25-30% compared to ad libitum feeding.
Chronic myocardial disease is commonly referred to as cardiomyopathy or chronic progressive cardiomyopathy and can first be observed as early as 3 months of age. The disease may exhibit the following pathology in lab rats:
There are a variety of hair and skin abnormalities across various lab rats, often attributed to strain backgrounds, gender, and age.
Pulmonary alveolar histiocytosis is very common in the lungs of aged rats from many populations and strains. Pulmonary alveolar histiocytosis is unrelated to viral pneumonia, as affected animals are seronegative, and lymphocytic infiltration is minimal, limited to areas of macrophage aggregation. The etiology of pulmonary alveolar histiocytosis is not clear but can be ruled out as infectious.
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Fox J G, Anderson L C, Otto G, et al. Laboratory Animal Medicine:Third Edition[M]. 2015.