ASPECTS OF KEEPING RATS AS A DOMESTIC PETS

HOUSING

Rats and mice can be successfully housed in either commercially produced or home-made cages. It should be remembered, however, that they are likely to chew through wooden or plastic containers, so that metal or glass cages are to be preferred. A separate sleeping compartment is usually provided in commercially made cages, although this is not necessary if plenty of suitable bedding is available.

Caging often tends to be too small; rats and mice make entertaining pets if given room for additions to their environment such as exercise wheels, ladders, hollow tubes and climbing frames etc., which encourage exercise and help prevent boredom. A cage size of 45 x 30 x 25 cm high could house two or three mice, or one rat. Increasing the floor area by about 50% would enable twice the number of animals to be housed. This should not be continued pro rata, however; several smaller cages are to be preferred to one very large one.

Bedding should be soft wood shavings, tissue paper or sawdust, and cages should be cleaned frequently (two to three times a week) to minimize odours and to help to minimize the risk of disease. Rats and mice should be housed indoors, ideally at temperatures of 15-27C (60-80F). Temperatures above 30C (85F) may cause heatstroke, particularly in overcrowded conditions. If cage lids are made of metal mesh, this must be fine enough to prevent escape of young animals, but strong enough to resist being chewed through.

FEEDING

Rats and mice should be fed commercially produced complete ration as their basic diet, and this may be occasionally supplemented with small amounts of varied food such as apples, tomatoes, and biscuit. Rats are particularly fond of chocolate and cakes, and small quantities of these items an useful in encouraging the animal to respond to its owner. Rats and mice are very tolerant of changes in their diet, but this may lead to feeding of an imbalanced diet, or to overfeeding which can result in obesity. Water must be made available ad libitum.

RESTRAINT

Rats rarely bite, unless frightened or in pain, and should be picked up by placing a hand around the shoulders. It is important to hold the animal firmly but to avoid grasping it so tightly that it is prevented from breathing. If this occurs the rat will panic and may bite the handler. Picking up a rat by the scruff can cause it considerable distress and so should be avoided.

SEXING

Rats are considerably easier to sex than mice since the testes are visible even in juvenile animals. If problems are experienced the animal should be held vertically, which will cause the testes to pass from the inguinal canal into the scrotum. Neonatal rats are difficult to sex. The anogenital distance is greater (about double) in males than in females, although careful comparison is needed to distinguish the sexes.

REPRODUCTION

Rats are polyoestrous, with no specific breeding season.

Sexual maturity is reached at 8-10 weeks.

The oestrus cycle lasts 4-5 days.

Females are in season for 12 hours.

Pregnancy lasts 3 weeks.

Pregnancy can be diagnosed (with practice) by gentle abdominal palpation in the last third of gestation.

Mammary development is usually pronounced by day 15-16 in rats and mice. Nest building activity suddenly increases a few days before birth, and large nests of bedding material are prepared. Typically there are 5-15 young in a litter. Following birth, the mother should be left undisturbed for 2-3 days, since excessive handling may cause the female to eat her young. This is a particular danger with rats. Rat pups are relatively immature at birth, are blind and hairless. They grow rapidly and can be weaned at three weeks.

With most pet rats, a population explosion can be a problem. To avoid excessive production of young, ideally single sex groups should be kept, preferably females. Since rats are social animals, they should be maintained at least in groups of two or more. If a breeding pair is kept, it is important to separate the male and female before the young are born, otherwise the parents are likely to mate within hours of parturition, leading to overproduction of young.

Malcolm Cleveland B.Vet.Med MRCVS. Walton Lodge Veterinary Group, Broadstone & Parkstone

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