The guinea pig has been a favorite pet in many western cultures since the late 1700’s. Guinea pigs originated in the Andes Mountains of South America and are particularly suited as household pets because of their gentle demeanor, easy of care and friendliness towards humans. Guineas are a particularly fertile animal, related to the Caviidae family of rodents but are neither pigs nor from Guinea. Guineas are still popular today in many South American countries as a food source because they require very little resources to maintain and breed extremely quickly.
Guinea pig breeding has evolved beyond food production needs and is now considered a popular past time for those keeping guineas as pets. Guinea pigs come in a variety of shapes colors and sizes from long to short hair and everything in between.
Similar to many rodent species guineas are able to breed year round, though typically have the largest litters during spring pregnancies. Guinea pig breeding is controllable if your take precautions. Guinea litters can contain 1-8 pups but are normally 3-4 pups in size. Guineas are born nearly fully matured with hair, claws and a full range of senses including sight. Shortly after birth they are able to move about freely and eat solid foods. Males reach sexual maturity 3-5 weeks after birth while females typically sexually mature 4-6 weeks after birth. They reaches adult maturity around 8-12 months of age and can live up to 11 years though the average life span is 3-6 years.
Since females are able to become pregnant within a month after being born guineas can and do breed and have litters several times per year. Even more amazing is the fact that a female can become pregnant after about 4 hours of giving birth (so it is extremely important to separate adult males and breeding females after birth if you do not wish to produce more litters!). Guineas breeding out of control sometimes happens if you do not watch your piggies. Gestation last between 60-70 days as pig pups are born at a late stage near full maturity. They normally do not require any assistance during birth all though a guinea pig that has not had at least one litter by the age of six months may have problems with pregnancy later on as the hip bones of females with fuse together without birth experience. If a females hipbones do fuse together giving birth after the fact can normally only be done by cesarean section, as natural birth is no longer an option.
Male and female pigs are nearly indistinguishable from one another by outward appearance and normally can only be told apart by an examination of the pubic areas. Guineas are extremely social animals so much that when co-habitation mothers have litters together they will share and nurse each others young if lactating. When raising and breeding them, it is important to handle and pet the young, shortly after birth to ensure bonding. Unlike some animals a human’s touch will not cause rejection by the mother in pigs. In fact the sooner and more often a newly born guinea pup is introduced to humans the better, as guineas imprint social bonds from an early age. If they are touched, handled and petted shortly after birth they will become far gentler and people friendly pets. Raising guinea pigs can be a fun and rewarding hobby if responsibility is taken to ensure mothers and pups are cared for properly.

Author: Lee Martin
Resource Site : http://www.Guinea-Pig-Lovers.com
Come to the site and look around. Lots of good information.
Also a Free Mini-Course, for anyone wanting more
knowledge about guinea pigs.