Guinea pigs make brilliant pets and so much so that breeding fanatics are passionate about reproducing great examples of the guinea pig genes. Previously, breeders have been made aware that guinea pigs should be bred before they reach a certain age, otherwise they can suffer with difficulty giving birth. It has previously been recommended that guinea pigs are bred before they reach 6 – 9 months of age, as this is when the pelvis can fuse.
When the pelvis fuses this can cause dystocia. This is where giving birth is difficult and often requires surgical intervention. However, in a study by Vieu et al. (2024) “Assessing Pubic Symphysis Evolution in Guinea Pigs”, the new research suggests that guinea pigs that are over one year old can still successfully give birth without signs of dystocia.
Let’s unravel the world of the pelvis in guinea pigs, and see what this might mean for breeders, particularly when it comes to breeding young females.
Guinea Pig Pelvic Anatomy: The Basics
The anatomy of the guinea pigs pelvis is important to understand when it comes to reproduction. Like many mammals, their pelvis consists of several bones that support the lower part of the body as well as providing a birth canal.
The pelvis of the guinea pig is made up of three bones on each side called the ilium, ischium and the pubis. When guinea pigs are born, they are substantially more developed than many mammals and are pretty much self-sufficient in looking after themselves. However, this means that they require more space in the pelvis in order to be successfully birthed due to their advanced progression in the uterus.
The pelvis also consists of a cartilaginous joint located at the midline of the pelvis. In many mammals, this joint remains flexible throughout their lives in order to help with the birthing process.
Pelvic Fusion
However, in guinea pigs, it has previously been suggested that the cartilage in the pelvis of the guinea pig fuses and turns to hard bone. This means that by a certain age, the fixing of the pelvis increases the risk of dystocia due to the pelvis not being as flexible and therefore making it difficult for pups to pass, resulting in surgical intervention.
In mammals such as rats and mice, the flexibility of the pelvis remains the same throughout their lifetime in order to birth multiple young. Guinea pigs were thought to face more substantial challenges due to the fusing process.
In a bid to avoid breeding difficulties, guinea pig breeders often aim to breed females before 6 – 9 months of age, believing that breeding them earlier may allow their pelvis to remain flexible for future pregnancies.
More recent studies, especially that as provided by Vieu et al., suggests that some female guinea pigs can still successfully give birth even after the period where the pelvis would have been believed to be fused without any signs of dystocia.
As a result of this, the theory of pelvic fusion could be discounted, as it could be suggested that fusion may happen later in life – or even not at all in some cases!
The New Study: Key Findings
In this new study, researchers investigated the pubic joint of breeding and non-breeding female guinea pigs. They examined the pelvis by using a CT scanner, with the main motive being to discover whether the pelvis fused in female guinea pigs who did not breed before they were over 12 months of age.
The study looked at 23 female guinea pigs. They were grouped into 11 pairs, with one female in each pair selected for breeding and the other kept as a non-breeding control, allowing researchers to make a direct comparison between the two groups. Each guinea pig underwent multiple CT scans between the ages of 3 and 12 months, which aimed to measure the bone density of the pelvis, along with the width of the pubic joint.
One of the main key objectives of the study was to determine whether the pubic joint of the non-breeding females would fuse, leading to a reduction of flexibility, a previously thought cause of dystocia.
Interestingly, the study found no evidence of fusion of the pubic joint in any of the female guinea pigs throughout the set period. The width of the joint did not significantly differ between the breeding and non-breeding guinea pigs, however, the width did increase after birthing a litter. This is a significant discovery, as it has directly contradicted the previous assumption that guinea pig pelvises fuse and is the causative agent of dystocia.
No significant bone density changes were observed, with the study concluding that the widening of the pelvic changes was due to pregnancy and not due to fusion. This research helps to shed light on the misconceptions of pelvic fusion in guinea pigs.
Why This Discovery Matters for Breeding Guinea Pigs
Breeding guinea pigs may change dramatically following this new study, however, some breeders may still wish to abide by the rule of age markers. However, the assumption that the pelvis fuses at a certain age could be described as unreliable.
In younger guinea pigs, it has been standard to assume that the pelvis fuses after around 9 months of age and that the guinea pig is now no longer able to be used for breeding. Breeders may have been reluctant to breed following this knowledge, however, with the findings of the study by Vieu et al. it could be safe to say that this knowledge is not as relevant as we first thought.
With the study suggesting that pelvic fusion may not occur as a sole result of age, this means that breeders should use caution when relying exclusively on pelvic fusion as a theory on dystocia in guinea pigs. It may be worth consulting with a veterinary surgeon before breeding so that a range of markers can be assessed such as age, overall health and previous breeding background.
It is advised that a more comprehensive approach to breeding is implemented, with breeders and vets working together in order to come up with a safe plan of action.
Conclusion
The study by Vieu et al. contradicts the long standing belief that a guinea pigs pelvis fuses once they reach a certain age. For years, breeders (and probably vets too!) have been advised to breed females before 6 – 9 months of age, based on the fused pelvis theory causing dystocia.
However, this new research reveals that pelvic fusion may not occur as consistently as we first thought – and in some cases, may not even occur at all!
If anything, the study has shown the importance of a full clinical assessment before deciding to breed guinea pigs, instead of relying on age as a sole factor.
With these new findings in mind, it may be time for guinea pig breeders to update their practices and work closely with vets to ensure the best possible outcome for their animals. For the veterinary industry, it is important that studies like this continue to develop and reshape our knowledge so that we are giving the best advice to owners and breeders.
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