The most common pet rat (Rattus norvegicus) and the mouse (Mus musculus) are both rodents of the family Muridi. These two species are the ones most likely to be kept as pets and they are often also kept to show standards and exhibited. They have been kept and bred for exhibition purposes for at least one hundred years. There are numerous different classifications of mice.

Rats and mice can be very suitable pets for both adults and children alike. Rats in particular make extremely good pets as they rarely bite, especially if well socialised from an early age, and they display far more individual personality than mice and can be trained.

Rats tend to be rather more nocturnal than mice and will often spend most of their day asleep, thus they make good pets for those of us who are out at work all day. Mice, however, tend to be far more active and can move faster than rats. They may leap out of a small child's hands, so be careful! They cannot be trained in the same way that rats can. However, the more enrichment and time you spend with them, the more their personalities will come accross.

As a rough rule the males tend to be more docile than the females. Males do tend to smell rather more than females, however neutering will reduce the smell to some extent. Many female rats will develop mammary tumours (breast cancer) later in life. Both rats and mice do benefit from being housed with a companion of the same species, and they will then demonstrate a wide range of behaviours when group housed. A pair of rats or mice from the same litter will often live together for the whole of their lifetime without fighting, however introducing adult males to each other is not recommended. It is easier to introduce older females of both species.

Life expectancy of a mouse is between 1.5 - 2.5 years, whilst a rat is that of 2.5 - 3.5 years. A rat becomes sexually mature at between 6 and 8 weeks of age. Pregnancy lasts between 20 - 22 days and they then have a litter of 6 - 16 babies. A mouse reaches sexual maturity between 6 and 7 weeks of age. The pregnancy lasts for between 19 - 21 days and they produce between 6 - 12 babies with an average of 8.

Determining the sex of your rat or mouse is performed by comparing the shorter distance between the anus and the vulva in the female and the longer distance between the anus and the penis in the male. Rats are easier to sex than mice as the testicles are even visible in a baby, and generally, both newborn rats and mice are much harder to sex than adults. Where more than one sex is available, comparison does enable distinction to be made more easily.

HOUSING:

Rats and mice like to chew and so a cage made of wire with a solid plastic bottom, or an aquarium with a mesh roof is recommended. The former is preferable as this has better ventiation. Frequency of cage cleaning should be balanced against the stress that it causes by the removal of scent marking that the mouse or rat will have made to determine its territory. The cage should be sufficiently big enough for the occupants to exercise and allow them to have a degree of environmental enrichment. It should provide them with a shelter, a bolt-hole and a place to sleep. The cage floor should be covered with an abosorbent substrate such as sawdust or woodshavings, with nesting material, e.g. shredded newspaper or even commercial bedding. Some of the diet should be scattered in the sawdust to allow forraging and there should be provision of other environmental enrichment including empty carboard boxes, sheets of paper to chew up, drain pipes suspended from a lid and even an exercise wheel. Exercise wheels should have a solid back to prevent their long tails being caught in the side supports as the wheel turns. It is important, where possible, to give the pet 'out of cage' time, allowing them the run of the room or even the house, to improve bonding between the rodent and the owner.

DIET:

Rats and mice are both omnivorous and herbivorous. Ideally feed them on a commercial rodent diet that can then be supplemented with a wide variety of fresh fruit and vegetables in moderation. However, excessive supplementation can result in dietary imbalances, obesity and tummy upsets. It is important to make sure that the food bowl is heavy enough to avoid being tipped over. Water should always be made available.

COMMON DISEASES:

As they spend a considerably large portion of their time grooming, which keeps their coat well kempt, clean and shiny, signs of ill health are frequently reflected in their external appearance, where the coat can become ruffled and staring. When ill they will also eat and drink less, and lose weight. Their activity will decrease and they may display a characteristic clinical picture of a hunched rodent with an unkempt coat, often isolated from their cage mates, and disinterested in their surroundings.

Most common diseases include dental disease. In contrast to the molar teeth, the incisor teeth at the front are open rooted and so can over-grow. This particularly occurs where the upper and lower incisors are not meeting (malocclusion). This may be an inherited condition, or can be due to trauma. One of the more common causes is gnawing on the cage bars, causing a loosening of the tooth root. Treatment is by regular trimming, often every 4 - 5 weeks. Clipping with nail clippers may shatter the teeth, so ideally burring them with a dental burr is best.