Why Are My Hamsters Balls So Big? Explained

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As a veterinarian, funnily enough I am quite often faced with the following question from concerned (or curious) pet owners: “Why are my hamster’s balls so big?!”

This article will discuss the normal and abnormal reasons why this might be the case.

Firstly, as a quick overview, the most common hamster species kept as pets are the Syrian or Golden hamster (Mesocricetus auratus), the Chinese hamster (Cricetulus griseus), and the Roborovski dwarf hamster (Phodopus roborovskii). This article can be assumed to apply to all three of these species.

So – let’s talk about hamster testicles and the three most likely reasons why your hamster’s balls might be so big.

It’s Often Normal In Sexually Mature Males

The surprising truth of the matter is that male hamsters have notoriously large testicles (as a proportion of their total body size) in comparison to the majority of other mammals…so, if you’ve noticed your hamster has large balls, there’s a good chance that this is normal.

The testicles of a male hamster grow dramatically once they reach sexual maturity.

This occurs at 8-10 weeks of age for Syrian hamsters, and for Chinese hamsters, it happens at around 8 weeks of age. The Roborovski dwarf hamster wins the award for speed in this instance however, reaching sexual maturity as early as five weeks of age.

Once maturity has been reached, you should expect your hamster’s balls to increase in size as a perfectly normal part of “growing up”!

Hamster eating — Photo by Sharon Snider on Pexels.com

2. Seasonal Changes

Whilst hamsters who are kept as pets may be able to breed year round, in the wild these same species of hamster are seasonal breeders by default. As such, seasonal factors play a large part in telling your hamster’s body whether or not peak sperm production is needed.

Day length (specifically, the number of hours of sunlight or artificial light your hamster is exposed to per day) is an especially important factor in determining how much sperm your hamster will be producing, and (resultantly) how large their balls appear! Ambient temperature is also an important factor.

For example, studies have shown that when Syrian hamsters are exposed to more than 12.5 hours of light per day, their body will assume that it is breeding season, and increased sperm production (and testicular size) will result!

On the flip side of the coin, if your hamster is kept in a dark room for much of the day, their body will assume it is not breeding season and their testicles will be comparatively small and inactive.

3. Testicular Tumors

Unfortunately, testicular tumors are also a possible reason for a hamster’s testicles to appear enlarged. You should be particularly suspicious of a tumor if one testicle is noticeably larger than the other, or if one or both testicles feel firm and/or “knobbly” to the touch.

Testicular tumors in hamsters can be either benign or malignant. Benign tumors do not tend to spread to other organs of the body, but may still cause problems by becoming large or ulcerated.

Malignant tumors are those which have the potential to spread (via the blood or lymphatic systems) to other organs in your hamster’s body, causing a more widespread cancer.

It goes without saying, of course, that if you believe there is a chance your hamster might have a testicular tumor, you should get them checked out by a vet without delay.

Important Key Points

Sexually mature male hamsters can have really big balls compared to their body size; often, this is completely normal in terms of their anatomy and physiology!
Seasonal factors such as day length and temperature can significantly affect testicular size in adult male hamsters.
Male hamsters can develop testicular tumors; if in doubt, take your hamster to a veterinarian with experience working with small exotic pets.

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