Breeding
A female Guinea pig could well produce five litters a year. Finding good homes for so many offspring can be a major problem, so the golden rule about breeding from pet Guinea pigs is: don't. Owners who want to breed from pure-breds would be well advised to join a good local Cavy/Guinea pig Club and acquire a thorough backround knowledge before beginning to breed from their stock.
As a general rule it is inadvisable to breed from young females of any species who may have reached puberty but who are too immature in behaiviour to deal with their own young patiently and competently. The same applies if they are too physically immature for the pelvis to have reached an adequate size to prevent pain and difficulty (dystocia) during the birth process. The case of the Guinea pig is rather different. There may be a greater risk of dystocia if the Guinea pig does not have her first litter while she is still young. Once fully grown, the pelvic bones fuse, leaving her with a rigid, perhaps under-sized pelvis, and this may cause differcult births and a shorter breeding span than normal. For this reason it is recommended that Guinea pigs should be mated at a relativly young age, maybe as early as 12 weeks. The litter will then be born before the mother reaches full maturity, and before the two halves of the pelvis fuse firmly together. However, with a sow that is slow to mature it may be advisable for her not to breed before she is six months old. A vet would have to advise on individual cases. Subsequent births should be trouble-free. Many females first mated when very young breed successfully and easily beyond the age of 18-24 months, which is usually quoted as the time to retire Guinea pigs from breeding. Even so, it is advisable, as always, to retire the older stock from breeding to make way for younger and more vigorous animals to continue a healthy line.
So it is better if the boar and sow are seperated for periods, to avoid chances of pregnancy. In particular, many owners find it advisable to house a pregnant sow alone for a week or two before her litter is due, because she needs very careful handling and quiet conditions during this time, and to leave her alone to bring up her family until weaning age. If the boar were left with the sow she would be likely to become pregnant again immediatly after giving birth.
As a general rule it is inadvisable to breed from young females of any species who may have reached puberty but who are too immature in behaiviour to deal with their own young patiently and competently. The same applies if they are too physically immature for the pelvis to have reached an adequate size to prevent pain and difficulty (dystocia) during the birth process. The case of the Guinea pig is rather different. There may be a greater risk of dystocia if the Guinea pig does not have her first litter while she is still young. Once fully grown, the pelvic bones fuse, leaving her with a rigid, perhaps under-sized pelvis, and this may cause differcult births and a shorter breeding span than normal. For this reason it is recommended that Guinea pigs should be mated at a relativly young age, maybe as early as 12 weeks. The litter will then be born before the mother reaches full maturity, and before the two halves of the pelvis fuse firmly together. However, with a sow that is slow to mature it may be advisable for her not to breed before she is six months old. A vet would have to advise on individual cases. Subsequent births should be trouble-free. Many females first mated when very young breed successfully and easily beyond the age of 18-24 months, which is usually quoted as the time to retire Guinea pigs from breeding. Even so, it is advisable, as always, to retire the older stock from breeding to make way for younger and more vigorous animals to continue a healthy line.So it is better if the boar and sow are seperated for periods, to avoid chances of pregnancy. In particular, many owners find it advisable to house a pregnant sow alone for a week or two before her litter is due, because she needs very careful handling and quiet conditions during this time, and to leave her alone to bring up her family until weaning age. If the boar were left with the sow she would be likely to become pregnant again immediatly after giving birth.
Special Considerations
Pregnant females drink thirstily and will take milk as well as water. Their diet must be increased to support the unborn or suckling young and if there are more than three in the litter they will need extra milk since she has only two mammary glands.
It has already been said that Guinea pigs are intolerant of low temperatures, and they are liable to suffer heat exhaustion. A heavily pregnant sow is particularly vulnerable in this respect. If she is kept in a hutch it must be moved to a shady position and hosed with cold water.
It has already been said that Guinea pigs are intolerant of low temperatures, and they are liable to suffer heat exhaustion. A heavily pregnant sow is particularly vulnerable in this respect. If she is kept in a hutch it must be moved to a shady position and hosed with cold water.
The Young
The delightful young of the Guinea pig are born with full coat, with their eyes open and their teeth already cut. They are able to move around by supporting 
their weight on their legs, and they attempt to take solid food within a day or two. This exceptional maturitly at birth make them the loveliest of all the usual pet rodent babies. They are born after a long gestation of about 63 days, usually in rather small litters, and single births are not uncommon. Average birth weight for the female is 85g (3 oz) and 90g (3½ oz) for the males. Single birth weights may be as much as 150g (5½ oz).
Because they are so well-developed at birth, there is very little likelihoodn of new-born guinea pigs being at risk from their parents, as is the case with mice, rats, rabbits and gerbils.
It is very tempting to show off such enchanting youngsters to your friends and family, but this should be resisted for a few days. However, you should check carefully that there are no dead or sickly young, and that they are all suckling well.
Suckling continues for about three weeks, but the young are best left with the sow until the age of four or five weeks when they weight perhaps 250g (8½ oz). There is no danger in leaving both the sow and the boar with the young to live as a small colony, although of coarse there is the risk of the sow becoming pregnant again.
their weight on their legs, and they attempt to take solid food within a day or two. This exceptional maturitly at birth make them the loveliest of all the usual pet rodent babies. They are born after a long gestation of about 63 days, usually in rather small litters, and single births are not uncommon. Average birth weight for the female is 85g (3 oz) and 90g (3½ oz) for the males. Single birth weights may be as much as 150g (5½ oz). Because they are so well-developed at birth, there is very little likelihoodn of new-born guinea pigs being at risk from their parents, as is the case with mice, rats, rabbits and gerbils.
It is very tempting to show off such enchanting youngsters to your friends and family, but this should be resisted for a few days. However, you should check carefully that there are no dead or sickly young, and that they are all suckling well.
Suckling continues for about three weeks, but the young are best left with the sow until the age of four or five weeks when they weight perhaps 250g (8½ oz). There is no danger in leaving both the sow and the boar with the young to live as a small colony, although of coarse there is the risk of the sow becoming pregnant again.