American Fancy Rat & Mouse Association

This article is from the Spring 1998 AFRMA Rat & Mouse Tales news-magazine.

Beginners’ Corner

Missing Fur; Sexing Rats
Missing Fur

Leonie Baldock, Somerset, Tasmania
QI have a 6-month-old female Hooded cinnamon and white rat. She has just weaned a litter of 14 babies. After raising them all, she has lost patches of her fur. It’s been over a month now. Her fur has not grown back. I have looked in books and pet shops and no one can help me.

To me it looks like a moult. She has no sores on her at all and there are no mites. I clean her cage out twice a week and she is on her own.

AThere are two likely possible causes for your rat missing patches of fur. The first thing that springs to mind when a rat is missing patches of fur is some kind of parasite. Mites and lice can be treated with a diluted cat flea shampoo, flea powder, or better yet, Ivermectin from your vet. If parasites are the problem, most rats will do a lot of scratching and will have some sores or small scabs.

Rat with chewed patch on shoulder
This female has a patch of fur chewed off of her shoulder by another cage mate.
Pregnant rat chewed fur off belly
This pregnant female has chewed off all the fur on her belly. It grew back after the babies were born.

In this case, however, there is another likely cause. Some rats have a tendency to barber themselves. They chew off patches of their own fur, trimming it right down to the skin. This is usually seen on the front legs or underbelly.

The reason for this kind of barbering is not completely understood. In many cases it is simply boredom caused by housing that is too small or unstimulating. Essentially they chew on themselves because there is nothing better to do.

This behavior is also frequently seen in females who have recently had a litter of babies. It is suspected that it may be a hormonal problem, or caused by the stress of raising the litter. Usually the behavior simply peters out over time. Nichole Royer

Sexing Rats

Joe Beaudry
QPerhaps this is a foolish question but I must ask it: How does one go about determining the sex of a rat? I adopted a group of five from a friend’s feeder tank and took them home. I would like to pair them off according to sex so that each rat can have a roommate, but I don’t want to have to worry about them breeding. I already have two rats plus three hamsters, so I would like to keep the population level of my menagerie at a manageable level. Looking at all of them, there seems to be no difference. Nothing I can identify as male or female genitalia.

AActually your question’s not foolish at all, far too many people don’t ask this question and end up with many unexpected or unwanted litters. It’s fairly simple to differentiate male from female rats. The only time it may be difficult is when they are very young (under 6 weeks old).

Side view of a male rat.
Side view of a male rat.
Bottom view of male rat
Bottom view of a male rat.

Side view of a female rat.
Side view of a female rat.
Bottom view of female rat
Bottom view of a female rat.

Male rats have very large testicles when compared to their body size. When looking at the underside of the rat, they appear as two oblong shapes and are located at the base of the tail. In an adult male they may be as much as 2″ long, and it isn’t unusual for people to mistake them for tumors. The testicles descend into the scrotum when the males are 4–6 weeks old, so should be easily distinguishable after that age. Females naturally have nothing in comparison to the males.

Diagrams of male & female rats.

Sexing very young rats can be rather challenging, and since it’s very hard to describe, it’s better illustrated. Lorryta Bowker and Nichole Royer *

Go to Sexing 101 page.

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Updated April 2, 2019