Lab Rat Care Essentials: Managing Non-Infectious Disease in Research

Genetic Predisposition to Disease

For decades, each population and strain of experimental rats has been carefully selected to possess specific genetic traits, such as albinism and characteristics associated with certain tumors. However, these traits are not universally desirable for all researchers.

Besides the known and induced genetic variations in rats with specific traits, spontaneously occurring genetic drift inevitably occurs in isolated breeding populations of rats. While genetic drift can be monitored in inbred rat strains through molecular techniques, it is challenging to assess the extent of its occurrence in closed populations, where individual variations may mask differences at the population level.

Nevertheless, any two populations originating from the same source will gradually change over time unless there is sufficient and consistent breeding exchange between the populations.

Nutritional Disorders Lab Rat Models

• High-pressure sterilization of feed reduces the vitamin levels, particularly lysine, vitamin A, vitamin E, riboflavin, and thiamine. Prolonged storage has a similar effect.
• Additionally, maintenance diets designed for adult rodents may have protein and fat levels that are too low to support the rapid growth and successful reproduction of juvenile mice.
• Clinical manifestations of inadequate feed nutrition may include lighter body weight, decreased reproductive performance, reduced litter size, poor growth, and sparse fur.
• Symptoms of severe deficiency of specific vitamins are rare. These include squamous epithelial metaplasia of the salivary ducts with vitamin A deficiency, diffuse hemorrhage with vitamin K deficiency, embryonic death and testicular degeneration with vitamin E deficiency.
• Nutritional deficiencies can also alter susceptibility to diseases and their severity.
• In addition to the total calorie level and specific nutritional components of the diet, it is important to consider the quality of feed, including chemical contaminants, microorganisms, and the size and hardness of feed particles. For instance, powdered feed can increase the occurrence of dental malocclusion.

Colony Management-Related Diseases

• Poor husbandry practices can lead to a wide range of health issues, including those related to experimental procedures.
• Maintaining the cleanliness of animal cages, bedding, water and food, as well as laboratory equipment, is crucial.
• High moisture content in bedding can lead to rapid bacterial growth, increasing the incidence of urinary tract infections and potentially causing mammary gland inflammation and skin lesions. Bacterial urease production in the saturated area of bedding can elevate ammonia levels.
• High moisture content in feed can potentially increase environmental fungal spore contamination through the proliferation of molds. Considerations for air quality may also include factors such as ammonia levels, carbon dioxide levels, dust, residual disinfectants, and pollutants.
• Rats are highly sensitive to factors such as temperature, humidity, noise, vibration, light, indoor activity, and other perceivable environmental changes. Tail necrosis symptoms are associated with relative humidity levels below 40%, but other factors may also be involved. Tail necrosis is primarily seen in young rats, typically nursing pups, characterized by the formation of distinct ring-like constrictions on the tail and toes.
• Rats, especially albino rats lacking protective iris pigment deposition, are prone to retinal degeneration when exposed to environmental light levels above a certain threshold. This threshold depends on light intensity, the duration of the light-dark cycle, and the previous exposure of the animals to light levels. In addition to pure retinal damage, exposure to high-intensity light at 1600 lux for 12 hours daily for 8 days can lead to Harderian gland necrosis, which may be a consequence of the photosensitivity of porphyrin secretions.

Injuries and Iatrogenic Diseases

• Traumatic injuries are not common in rats. Compared to mice, group-housed rats are much less likely to sustain injuries from fighting.
• There have been reports of ulcerative dermatitis in rats, associated with Staphylococcus aureus and self-inflicted scratching.
• Paralytic ileus can occur following intraperitoneal injection of chloral hydrate and may sometimes lead to death. This condition shares similarities with the pathological changes caused by Tyzzer's disease in young rats, making them prone to confusion. Clinical symptoms typically manifest a few days after anesthesia, including lethargy, anorexia, and abdominal distension. The most pronounced dilation occurs in the jejunum, ileum, and cecum.

Enhancing Research Outcomes Through Lab Animal Enrichment

• Environmental enrichment is a critical component of modern biomedical research, designed to improve the psychological and physical well-being of laboratory animals. By incorporating nesting materials, social housing, and structural complexities into the habitat, researchers can significantly reduce stress-induced behaviors and physiological variability.
• Properly implemented enrichment not only meets ethical standards but also enhances the scientific validity of experimental data. For lab rats and other rodents, these sensory and motor stimulations foster more natural behavioral patterns, ensuring that phenotypic observations are a result of experimental variables rather than a byproduct of environmental boredom or distress. At Cyagen, we prioritize these humane standards to deliver more reliable and reproducible research models.

Reference

[1] Fox J G, Anderson L C, Otto G, et al. Laboratory Animal Medicine:Third Edition[M]. 2015.