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sharing Aniphe BioLab’s achievements in scientific innovation, Professional insights
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Essential Tips | Rearing Techniques for Aged Mice (Part 1)

I’m sure many of you have been frustrated by the occasional fights among senior rats, and some newcomers to the world of senior rats may not yet be fully familiar with their needs. Today, we’re here to address your questions and shed light on everything you need to know about senior rats.

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There are many strains of aged mice, with the following being commonly available on the market: C57BL/6J mice, APP/PS1 aged mice, and SD aged mice.

As these laboratory mice age, they exhibit natural aging characteristics: their disease profiles resemble those of humans, they become irritable and prone to aggression, displays of fighting are pronounced, their fur lightens and thins, and their overall condition deteriorates.

Therefore, before housing these aged mice, it is essential to thoroughly understand their behavioral habits, age-related characteristics, and the key considerations for their care, in order to minimize unnecessary losses.

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Taking the most common C57 elderly mouse as an example:

C57 mice are naturally aggressive. ， Following sexual maturation in males, heightened territoriality intensifies intrasexual aggression; in particular, mice are more prone to fighting after retirement.

In addition, aged C57 mice exhibit several other characteristics:

1) The coat color lightens, and some white hairs appear.

2) Sparse coat

3) They enjoy grooming. Grooming is a social behavior in mice, used to assert their position within the group; lower-ranking mice, due to frequent grooming by others, may experience hair loss or bald patches—most commonly around the whiskers and on the back.

4) Due to their inbred nature, aged C57 mice develop spontaneous tumors, with the incidence increasing with age (typically beginning around 18 months of age).

5) Healthy mice can live for 18 to 24 months; however, according to caretakers’ observations, their condition begins to decline gradually after 18 months of age.

In AD model mice—namely APP/PS1 (double transgenic), APP/PS1/Tau (triple transgenic), and 5×FAD (quintuple transgenic)—age‑related changes mirror the disease state observed in humans, as evidenced by: Irritability and fighting within the group have increased.

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Given the characteristics outlined above, what should we pay attention to when raising them?

1) When caging, avoid placing mice from different cages into the same cage whenever possible.

Tip: Laboratory mice in the cage have lived together since weaning; if they are housed with unfamiliar cage mates, they will naturally fight.

2) When replacing the bedding, set aside a small amount of the original bedding and place it on top of the new bedding to preserve the familiar scent. Use the original cage or enclosure whenever possible.

Tip: If you are not using the original cage racks, be sure to thoroughly scrub and clean the removed cages, followed by complete disinfection and sterilization, to minimize residual odors that could irritate other laboratory mice.

3) Reduce stocking density: It is recommended to house 2–3 animals per cage; when aggression among animals is severe, adopt a single-animal-per-cage housing system.

4) Place the animal housing cage in a quiet environment, maintaining a certain distance between the cage and the walls to minimize excessive noise, vibration, and other disturbances.

5) Observe the experimental mice daily. If fighting is observed in the cage, select the strongest individual—free of injuries and with intact whiskers—and house it in a separate cage. At the same time, disinfect any injured animals daily with 75% ethanol or iodine tincture; typically, they will recover within 5–7 days.

6) Adding nesting materials to the bedding (such as shredded paper, cardboard tunnels, and shelters) can reduce grooming and fighting behaviors.

7) Evidence indicates that placing a wrung‑out iodophor‑impregnated cotton ball inside the mouse cage can reduce the occurrence of fighting.

8) It is recommended to conduct the experiment only after a one-week acclimatization period.

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For more tips on animal care, visit Aniphe BioLab—feel free to contact us!

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