Rat Colony Health at a Glance
Source: AEMV guidelines, Quesenberry & Carpenter, NC3Rs
| Disease | Cause | Prevention | Treatment |
|---|---|---|---|
| Mycoplasmosis | Mycoplasma pulmonis | Ventilation, low-ammonia bedding | Doxycycline (chronic mgmt) |
| Mammary tumors | Hormonal (intact ♀) | Spay before 3 months | Surgical excision |
| Bumblefoot | Wire floors, obesity | Solid floors, weight mgmt | Antibiotics, bedding change |
| Respiratory infection | Ammonia, stress | Clean cage every 5-7 days | Enrofloxacin + doxycycline |
| Step | Duration | Method | Success Criterion |
|---|---|---|---|
| 1. Quarantine | 2 weeks | Separate room | No signs of respiratory illness |
| 2. Scent swap | 3-5 days | Swap bedding between cages | Calm response to new scent |
| 3. Neutral meeting | 15-30 min x 3-5 | Bathtub, neutral surface | Grooming, parallel rest |
| 4. Cohabitation | Ongoing | Freshly cleaned cage | No fighting, shared sleeping |
Colony Health Management Cycle
Rats (Rattus norvegicus domesticus) are social animals that must be kept in same-sex groups of 2-4 minimum -- solitary rats show chronic stress, shortened lifespans, and behavioral abnormalities. Keeping a colony of rats in good health requires understanding their primary disease risks: respiratory disease (mycoplasmosis), cancer (particularly in females), and fighting injuries. None of these is inevitable with proper husbandry, but all three are common in colonies kept without attention to ventilation, housing space, and population dynamics.
Mycoplasmosis: the respiratory disease that comes with almost every rat
Mycoplasma pulmonis is a bacterium carried by nearly all domestically bred rats -- transmission occurs at birth. Most rats live symptom-free for years; the bacterium becomes pathologically active under stress (inadequate ventilation, high ammonia from bedding, overcrowding, concurrent viral infection). Signs of active mycoplasmosis: clicking or rattling sounds when breathing, red-brown discharge around the eyes and nose (porphyrin -- a normal secretion but excessive amounts indicate illness), labored breathing, weight loss. Treatment: doxycycline 5 mg/kg twice daily for 3-4 weeks during flares reduces bacterial load and symptom severity. There is no cure -- management is suppression. Prevention: adequate ventilation (wire-barred cages, not aquariums -- aquariums trap ammonia), deep substrate cleaning every 5-7 days, low-stress environment.
Cancer rates in female rats require planning
Intact female rats have among the highest spontaneous mammary tumor rates of any mammal -- studies show 40-80% of intact female rats develop mammary tumors, typically after 18-24 months of age. Mammary tumors in rats are palpable soft masses that appear on the ventral abdomen and chest and can grow to 10-20% of body weight, restricting mobility. Treatment: surgical excision is highly effective (benign adenomas are the most common type) and can be performed by an exotic veterinarian; survival post-surgery averages 1+ additional year. Early spay (ovariectomy before 3 months) reduces mammary tumor incidence by approximately 85% per published rat research. Spaying a colony of female rats early is a significant preventive investment that reduces late-life suffering and veterinary costs.
Introducing new rats to an established colony
Rats are territorial -- new rats introduced directly to an established colony will be attacked. Safe introduction protocol: quarantine new rats for 2 weeks (for respiratory illness monitoring), then begin scent introduction (swap bedding between cages for 3-5 days), then supervised neutral-territory meetings (bathtub, bathroom floor) of 15-30 minutes with close observation. Signs of compatible interaction: grooming, following, parallel rest. Signs of incompatible interaction: sustained fighting, bite wounds, tail rattling (alarm signal). After 3-5 successful neutral meetings, move all rats to a freshly cleaned cage simultaneously. This process takes 1-3 weeks but prevents the colony-disrupting injuries of direct introduction.
Housing requirements for rat colonies
Minimum space per rat: 2 cubic feet (larger is always better). Wire bar cages with 0.5" bar spacing for adults (smaller bars required for weanlings). Multi-level cages (Critter Nation, Ferret Nation) provide territory zones that reduce conflict. Substrate: recycled paper bedding (Carefresh, Eco-Bedding) 2-3 inches deep, changed fully every 5-7 days. Temperature: 65-80 degrees F. Avoid temperature extremes -- rats are susceptible to heat stroke above 85 degrees F. Hammocks, hammock cubes, and rope perches provide environmental enrichment. Rats that are bored will bar chew and fight -- rotation of toys (cardboard tubes, wooden blocks, foraging boxes) maintains environmental interest.
Signs that require veterinary attention
Seek exotic veterinary care for: respiratory sounds lasting more than 3 days (doxycycline treatment indicated), any lump or mass (surgical evaluation for mammary tumor), red eye discharge that doesn't resolve within 48 hours (porphyrin from illness -- not normal in quantity), significant weight loss despite eating, hind leg degeneration (HLD -- a progressive neurological condition common in older male rats; supportive care but not treatable), and any rat that is isolating from the group and not eating.
Sources: Quesenberry K. Ferrets, Rabbits, and Rodents; Hotchkiss CE, et al. "Early oophorectomy reduces mammary tumor incidence in rats." Laboratory Animal Science; Merck Veterinary Manual rat section; National Research Council. The Laboratory Rat; Rat Forum community care standards.