Kids & Pets
July 5, 2020
link to facebook link to twitter

One plus one equals twenty, rats that is

By: Mickey Zeldes
January 31, 2020

When does 1 + 1 = 20?  When a pair of rats purchased from a pet store are mis-sexed!  Which is the story we got when a family surrendered a mom rat and her 20 offspring.  It can be difficult to accurately sex some small animals, rats, mice, hamsters and even rabbits, when they are young and not fully developed.  But if you wait until they are developed, you have waited too long to separate the males from the females!  And that is when the math becomes tricky – the number of offspring grows exponentially meaning that in just three months you can be housing over 500 rats!  You can see how this can get you in trouble in no time!  Remember the story of the rat man in Petaluma several years ago that was found with over 1,000 rats in his home?  Didn’t take all that long for that to happen!

The hard part is female rats are fertile as soon as they give birth.  So, if you wake up one morning and find that your pair of (what you thought were sisters) rats have presented you with a surprise litter and you then pull out the male, you’re too late!  The mom may already be pregnant again!  Which is exactly what happened with the rats we received.  The 20 offspring were clearly of two separate litters since some were bigger and older looking than the younger babies.

Rats and other small rodents can start breeding quite young.  They need to be sexed and separated by four weeks old.  Crazy huh?  They are still tiny babies and yet by 4-5 weeks old they can start breeding themselves!  I guess when your lifespan is only a couple years you have to get busy early!  Their gestation is only 21-23 days too so they can have many litters in a year, although that is not healthy for the mom.  

We also got in three baby guinea pigs on the same day.  Although guinea pigs are considered rodents their babies are born precocial – fully furred and mobile, similar to horses.  Because of that, their gestation period is triple that of rats – the average being 63-68 days.  There is nothing cuter than a newborn guinea pig – they come out with their eyes open and ready to go!  They look just like mini adult piggies!!

The story for the guinea pigs, though, was the same as the rats.  A pair purchased from a pet store had been mis-sexed.  It’s important that you compare their genitalia carefully to make sure you are getting two that look identical!  If you have doubts we are happy to give a second opinion.  But know that animal shelters often have little pets available as well as dogs and cats and we encourage you to check there before buying from a pet store.  In my opinion they shouldn’t be selling animals in the first place and should just be a supply store.  We have partnered with a couple of the PetSmarts locally to house and help adopt out our rabbits.  This is a win-win for both the store, as they get to send home an animal with supplies purchased at the store, and the shelter that gets another venue to have their animals seen.

We certainly are well stocked with guinea pigs and rats at the moment!  If you, or someone you know, are thinking of getting a pair as pets (both are social animals so need to go out in at least pairs), please come by and take a look at our selection!  They grow up quick so better be quick to get them as babies.


Upcoming Events

Bark After Dark – a dinner and auction to help the animals!  Saturday, Feb. 22, 6:30-10 p.m.  Tickets now available at www. or at the RP Animal Shelter.  Come enjoy a fun evening and support the Animal Shelter League!!


Fix-it Clinics – Free spay and neuters for cats; and $100 dog surgeries (up to 80 lbs.) for low-income Rohnert Park and Cotati residents.  Call 588-3531 for an appointment. 


Mickey Zeldes is the supervisor at the Rohnert Park Animal Shelter. She can be contacted at