***Please Note: It's always safest, and kindest NOT to breed your girl if you don't have any reason to. Non-breeding guinea pigs will live long, happy lives if cared for properly - they certainly don't 'need' to be mated. In fact, after taking into consideration the risks faced by a pregnant guinea pig, even in the hands of someone with experience, non-breeding girls will probably live longer on average ***
This is just a run down on some of the most important information you'll need to know if you plan to breed your pet guinea pigs, or if you find yourself with a pregnant sow. My advice is to learn AS MUCH as you can now - before the 'big day' arrives, or before you make the move to house male and female guinea pigs together. It can be as straightforward as 'finding some new babies in the cage one morning', or it can be as devastating as loosing the bubs and/or mum for a variety of reasons...
1. Guinea pigs DO NOT change sex. They are born male or female. The 'changing sex' myth has only come about through many mistaken gender incidents!
2.It is possible to determine gender at birth if you are practised. Girl's have a more 'sectioned' and flatter look with a 'Y' shape, boys have a line with a penis bud at the top - kind of like an 'i' shape. You will also be able to feel the ridge of the penis just along the top of the genitals if you run your finger over the area gently. In older males, gentle pressure above the genitals will protrude the penis - pretty hard proof that you have a boy on your hands! Cavy Spirit have an excellent page on determining gender as well - lots of very clear photos. If you are still ever unsure, please get your guinea pig checked by an experienced vet or a breeder. I am also more than happy to sex guinea pigs of any age.
3. Male and female guinea pigs can become fertile between 4-10weeks of age. This is why it is so important to have gender correct from the beginning.
4. Females are safest not bred before 4 months (or before they reach 600g). Assess your sow and retire her before she gets too elderly/frail. We tend to retire our girls at between 2-3yrs of age. This way they will have delivered 3-4 litters over the course of those years, we've been able to keep the best offspring for continuing the lines, but don't need to tax her body any further.
5. But, pregnancy can be fatal for a female who is allowed to get pregnant for the first time after the age of 12months (the ligaments surrounding the pelvic bone can become rigid, meaning that the babies have no way to be born. In this situation she will need a c-section, which has a very poor survival rate for her and her babies). Please note that NOT all older females will have trouble, but there is an increased risk simply due to the physiology of getting older. Some girls have been known to have their first litter at 3yrs old, and do fine - you would have to have a long think about knowingly putting an older sow at risk like this though. I have personally had to watch one of my 16month old females (born at our caviary - but returned from her previous home pregnant), try to deliver her first litter with a 'fused' pelvis. She was rushed to the vet where she underwent a C-section. All 4 babies were dead, and she too passed about 2hrs post op. It often ends up being a costly, and traumatic exercise.
6. A female who has just delivered a litter is fertile again immediately following birth, so should not be left anywhere a male could get access to her. Back to back litters are incredibly stressful on their little bodies. It is best to allow at least 3-4 months rest between birth and re-introduction to a male if you wish to breed your female again. This will allow the female time to re-gain some condition. This will also give you approx two litters per year. More than enough for one little guinea pig! If your guinea pig has not handled pregnancy, birth or nursing very well then it is best not to breed her again. Next time you may not get such a good result.
7. It is possible to have a healthy litter of babies, only to loose the mum due to blood loss, infection, toxaemia, or a variety of other complications. If you can, try and time deliveries so that you have two females due together. If something happens to one mum, the other may be able to foster the orphans. If a mother dies within the first 24-48hrs,there are no other recently delivered mothers available to foster, and the babies are very small, you will need to supplement their diet with a suitable small mammal milk formula (Divetalact). Most vets should be able to point you in the right direction, or even sell you a suitable mix. In the past I have successfully used a kangaroo milk formula (this does not have the right balance of proteins/fats etc, but did keep the baby alive until he was old enough to survive on solids). I have also had good results using breast milk, though this will be hard for most people to come by! Now a days there is actually a guinea pig specific milk formula you can purchase, though it may be a bit hard to source. You will also need to mimic the mother's cleaning of the baby's bottom by gently wiping the bottom with a wet cotton ball to encourage the baby to defecate. This routine will need to continue until the baby is strong enough to survive on solids alone - usually at about 1 week old. I did have a litter of four sisters loose their mother suddenly at 4 days old though, and they thrived despite her absence. Guinea pigs are very resilient little creatures!
7. Something about the smell/hormones from a birthing guinea pig can prematurely bring on the labour of other pregnant guinea pigs if they are housed in close proximity to the birth-in-progress. This is not so much of a problem if you have mothers due very close together, but can be devastating if the other mum's are not near their due date. For the reason, I remove my pregnant females from the main group before I expect delivery.
8. A guinea pig's pelvic bone (just above her genitals) will open to approx 2-fingers width when she is about to have her babies. For most guinea pigs, this full dilation will occur about a day before birth. The pelvic bone will usually start to slowly open from 1-2weeks before full dilation.
7. Guinea pigs can miscarry their babies in some stressful situations or cases of poor mother/foetal health. In this instance, it is not uncommon for the mum to eat all/part of the foetus. This is a controversial topic in the guinea pig world with many denying it happens, but I have witnessed it first hand. Quite a few times. It is gruesome, but also an evolutionary behaviour, and occurs for similar reasons to the eating of the placenta after normal delivery. The guinea pig is trying to keep the area as clean and odour-free as possible so as not to alert predators that she has just given birth.
8. Guinea pigs can also accidentally injure their young when giving birth. If the baby gets stuck they use their teeth to help pull it out. If they panic or grab an ear/limb/body, they can seriously harm their baby. It is always worth while being present for a birth if possible.
9. Many perfectly healthy babies can die because a mother is inexperienced or distracted when cleaning her babies following delivery, and doesn't remove the membrane from the baby's face quickly enough. If you are present for a birth, and the mother hasn't made an attempt to break the sack then you will need to intervene. Give her space to do it herself first, but if you feel it has been too long, or she has chosen to continue to clean an older baby - gently pick the new baby up, break the membrane with your finger nail or rub it away with a clean towel. Pay attention to the face/nose. Gently rub the little body to help encourage the first breath. Once the baby is breathing, return it to it's mother so she can finish cleaning it and recognise it as one of her litter.
10. Be VERY careful about pairing up male and female guinea pigs with any roan hair in their coat. If you suspect roan colouring, my best advice is do not breed the animal unless you are certain their partner is roan-genetics-free. Roan x roan matings frequently produce genetically deformed pink-eyed white offspring called 'lethals'. If they are not born dead, or die shortly after birth then they are usually sentenced to a short, difficult existence. Information and knowledge is the key to stopping the unnecessary/accidental breeding of these poor creatures.
(Please note this is not my image - just one found on google. A search for 'roan guinea pig images' will give you an idea of all the different ways this gene can manifest in a coat)
In general, guinea pig pregnancy and birth come with some significant risks. Birth for mammals is a dangerous, but necessary event. None more so than for guinea pigs, who carry their young until they are very developed and exceptionally large (comparable to the average woman giving birth to a 3-yr old!). Breeding guinea pigs can be an incredibly magical experience, but more often than not it can also be heartbreakingly tragic. Please don't knowingly place a male and female together unless you feel competent to handle any of the very common pregnancy/birth/newborn complications, have a responsible plan for the resulting offspring and are able to do so with the utmost respect for your animals:
- Allow your female to get to an appropriate age.
- Keep her well fed, with lots of extra good quality food and vitamin c.
- Separate her from any males well before birth.
- Separate her from other pregnant females.
- Try and be present, but unobtrusive for the birth.
- Get any resulting babies sexed correctly as soon as you can.
- Separate baby boys from 3-4 weeks, depending on how quickly they start practising their 'horny dance'!
- Allow her a decent break (3-4months) before further litters, if any more at all.
If you have ANY questions at all about anything I've written on this page, don't hesitate to email me (firstname.lastname@example.org). This information has been compiled from my own experience and research over many many years! Also, if you think there is something I've have left out - please let me know! It's hard to choose what is the most important information!