Feeder Rat Care Sheet

Scientific name

The species is Rattus norvegicus, the brown or Norway rat in its domestic form. Feeder rats come from the same domestic species as pet and lab rats.

Adult size

Adult males weigh about 10.5-17.5 oz (300-500 g) and females about 7-11.5 oz (200-325 g). Sellers' largest classes (XL, jumbo, retired breeder) range from about 9 oz to 17 oz (250-475 g) or more.

Lifespan

Rats live about 2-3 years (18-36 months).

Enclosure

Use large tubs, a rat rack or wire-lid cages made of chew-proof, easy-to-clean material, with solid floors (wire floors injure feet). Rats produce far more urine than mice, so ammonia builds up fast. Ventilate strongly with rack airflow or well-vented lids, keep stocking density low, spot clean often and change bedding about twice a week. Ammonia damages the airways and worsens respiratory disease. Glass aquariums hold ammonia in and are a poor choice.

Paper-based, low-dust, unscented bedding is safest. Avoid cedar, untreated pine (aromatic oils) and scented bedding. Provide nesting paper and a hide. Lab guidance for density in a standard box of about 190 sq in (1,225 cm2) is up to 8 young rats under 200 g, about 3 at 200-500 g, or 2 over 500 g. Rats are strong, clever chewers, so lids and latches must be escape-proof.

Temperature

Keep the room at about 64-79°F (18-26°C). Rats tolerate heat and brief water shortages better than mice, but heat combined with humidity still risks heatstroke and worsens respiratory disease.

Humidity

Aim for about 30-70% relative humidity. Low humidity causes ringtail (a constricting ring and dead tail tip), mainly in young rats, while high humidity increases ammonia and respiratory disease. Bedding should stay dry.

UVB

UVB is not needed. Rats are nocturnal indoor mammals eating a complete pelleted diet that provides vitamin D, and nothing recommends UVB for feeder colonies.

Lighting

Use a regular day-night cycle with real darkness; many colonies run about 12 hours of light and 12 of dark. Keep the colony room dark and quiet at night.

Heating

A normal house usually needs no extra heat. In a cold room, warm the room or run a heat cable under part of a rack on a thermostat, leaving a cooler zone. Heat is the greater danger. For fire safety, keep cords, plugs and heat cables out of chewing reach and away from bedding, use rated thermostats, and never run heat without one.

Diet

Make a complete rodent lab block (laboratory or rodent breeder chow) the staple. Blocks are complete but can make non-breeding rats fat if free-fed, while growing young can eat freely. Occasional vegetables and a little fruit are fine, but cheap seed mixes and scraps give poorer feeders. Keep feed sealed, cool and dry, use it within about a year, and discard moldy or buggy feed.

Provide fresh water at all times from bottles checked daily. Open bowls get fouled, and young pups can drown in them.

Supplements

A complete lab block needs no supplements. For whole-prey feeders, the colony's own diet is the gut load. A well-fed rat is complete nutrition with its own skeleton as the calcium source, so calcium dusting is not normally done. Poorly fed colonies give less nutritious prey.

Shedding

This does not apply, as mammals do not shed skin like reptiles. Hair loss with scabbing or itching points to mites.

Handling

Lift a rat by the body, not the tail tip, because adults can bite seriously. Gloves should be worn when cleaning and when handling frozen feeders.

Allergies: rat urinary proteins are the main cause of laboratory animal allergy and occupational asthma. In one long-term study, nearly a third of rat workers reported work-related eye, nose, skin or chest symptoms, and sensitization rose with exposure. In big colonies, wear a dust mask or respirator for bedding changes, change bedding gently and keep the colony out of living areas.

Zoonoses: Seoul virus (a hantavirus) is carried by rats without signs and spreads through urine, droppings, saliva and dusty bedding. In a 2017 outbreak, 31 home and commercial ratteries in 11 US states were involved. Of 183 people tested in the US and Canada, 24 had antibodies (17 with recent US infections); none died, though 3 were hospitalized. Rat-bite fever (Streptobacillus moniliformis) lives in rats' noses and throats and can be fatal (7-10% untreated, and fast in some cases). Handling alone can pass it on, since about 30% of patients recall no bite. Frozen feeder rodents have been traced to national Salmonella outbreaks (in 2014, 41 people in 21 states).

Hygiene: wash your hands with soap and water as soon as you have handled rats, live or frozen, and avoid hand-to-mouth contact. Thaw away from the kitchen and food. Disinfect tubs (10% bleach or a commercial disinfectant). Clean any bite well and seek medical care, telling the provider you keep rats. New rats should be quarantined for about 4 weeks. The CDC recommends that ratteries test incoming rats for Seoul virus antibodies before mixing them in.

Brumation

This does not apply to living rats. For frozen stock, euthanize humanely, freeze promptly, label by size and date, and use within about 6 months. Thaw either in the fridge or by sealing the rat in a bag and setting it in warm water. Never use a microwave or oven, and do not refreeze a thawed rat that was not eaten. Large rats need many hours to thaw through, so feed only when fully thawed and warmed.

Health signs to watch

Chronic respiratory disease is the most common rat problem. It is mainly Mycoplasma pulmonis, sometimes with other bacteria or Sendai virus. Signs are sneezing, snuffling, red discharge around eyes and nose, labored breathing, and head tilt from ear infection. It cannot be cured, only eased, and the main factor you control is ammonia from dirty bedding.

The tropical rat mite feeds on blood, can cause anemia and death in heavy infestations, lives in bedding and bites people, so treat the environment too (vet advice). Mammary fibroadenomas are very common tumors in older females, often with pituitary tumors.

Other things to watch: overgrown incisors, kidney disease in older rats, ringtail in dry rooms and fight wounds between unfamiliar males. Discuss a colony-wide illness with a vet; it may mean culling and restarting with clean stock.

Welfare

Kill rats humanely, using only methods that the AVMA Guidelines for the Euthanasia of Animals accept for rodents: injectable barbiturates (through a vet), an overdose of inhaled anesthetic, carbon dioxide from a compressed gas cylinder with a gradual fill (not a prefilled chamber, and not dry ice), or decapitation, done only by trained, practiced people. Cervical dislocation is acceptable only for rats under about 200 g (7 oz), and only when trained people do it, ideally after sedation. Because newborn pups resist low oxygen, they need much longer CO2 exposure along with a second method to be sure they have died. Make sure the animal is dead before freezing. Never freeze, chill or drown a live rat. Freezing without prior anesthesia is not an accepted method.

Live feeding: never leave a live rat alone with a reptile. Rats bite hard and can maim or kill a snake, so remove any rat not taken within a few minutes. The usual recommendation is frozen-thawed or freshly killed prey, which is safer and lets freezing kill many parasites. Practices vary, and some keepers feed live to animals that refuse dead prey.

If a colony is confirmed for Seoul virus, CDC has recommended euthanizing the colony, so work with the local health department. Never release rats outdoors.