We've had guinea pigs all my life, I worked with rescues, and I get my information from the most comprehensive medical site connected to the most experienced vets working with guinea pigs. guinealynx.info warning- not a forum to set foot on if you're a breeder since it is maintained by rescues... ok so I will admit they are obsessed with guinea pig health and safety to the point of acting like a psychotic cult and that's why I don't even set foot on their forums anymore
but that's the reason they have the best info you will find anywhere. They are obsessed with guinea pigs and have found accomplished vets and researchers that are also obsessed with guinea pigs as well as digging up any past research done on guinea pigs. I will agree with anyone who thinks they are insane but I have to say they are rarely wrong and have the facts to back everything up.
The males actually mature sooner than the females but they don't always mate that early particularly if there are few adults around to scent and copy. Males can more often physically breed at 3weeks but may not try it for months if not given good reason. Females are more likely to take until 5-6 weeks but since coming into heat attracts a male to mate are more likely to get pregnant as soon as physically possible. Yes it is less common and dangerous for it to happen that young. A few months old is more common but I have seen obviously pregnant 3 month old females more times than I'd like and I've seen stunted young females give birth to singletons practically their own size because they got pregnant so young. Pet stores are bad for that. Even when
petsmart decided to make a male and female pen I often scooped one up to find it was in the wrong pen. I would say the average litter size is a bit higher than 1-3 if a female survives the first litter but those first litters drag the average down. Generally only first litters have 1 pup and I've never actually had it happen beyond the first litter. Singleton pups tend to have issues and result in more dead mothers or still births so basic evolution leans toward 2-3 in the first litter. Subsequent litters closer to 3 and the females we bred for many years and litters tended more towards an average of 5 with occasionally 7 and one litter of 9 with one runt that died. Since we tended to breed a couple females until they were too old or had complications before choosing new ones we had litters of 5 more often than litters of 3 or less but the official recorded average seems to be 3.
Guinea pig pups can absolutely, most definitely, without question survive without mother's milk. When it comes to breeding guinea pigs this is one of the biggest arguments the medical site and knowledgeable rescues have with breeders and other rescues as well as between exotics vets and vets that are not experienced with guinea pigs. Orphan guinea pig pups suffer more health problems and losses when given milk replacers than when just fed softened pellets, fresh foods, and hay. I have pics on photobucket of 3 one day olds with non lactating young females inhaling fresh picked alfalfa, grass, and lettuce as well as one of them eating whole unsoftened pellets a day later. They can do far more than nibble and will survive just fine without milk. Lots of pups have been raised with no milk and it's the standard by guinea pig rescues. 100s if not 1000s have been raised that way with no losses except to birth defects, accidents, and contagious illness passed from adult pigs. The nutritional content of guinea pig milk has been tested the same as every other milk (including domestic and cottontail rabbits) and is extremely weak. Finding the exact numbers again is difficult. They aren't as published as rabbit milk but it is bordering on useless since it has less fat and protein than even skim milk. Pups can be weaned within days and would suffer no physical effects if it weren't for the need of an adult to teach them things. Breeders using milk replacers for guinea pig pups are in my opinion idiots. All research and plenty of others experiences have shown that milk is unnecessary and quite possibly harmful to the pups.
Guinea pigs are extremely efficient eaters. It's actually one of the reasons they easily get fat on pelleted diets. They need more fiber than even rabbits and will be less efficient and have more health problems on a pelleted diet along with gaining excessive weight from the extra fat and protein that they don't need. They will be much more efficient, healthier, and reach a proper adult weight faster on a diet of fresh vegetables and forage. The next best thing is a mostly hay diet with daily fresh foods to provide things like vitamin c and a small amount of pellets (no more than 1/8th-1/4th cup per day per pig) to make sure they get everything they need. I fed mine for a while on entirely fresh foods during warm months and hay plus purchased vegetables in winter months. That was a pain though since I was weighing everything, looking it up in the USDA nutrient database or forage reports for livestock and then calculating all the ratios to make sure they had what they needed. Now I wouldn't have the time for it and would have to rely more on hay and pellets. Despite the fact they get fed whatever leftovers are in the kitchen like potato peels and have to hunt down bits of forage left in the area it could be argued that guinea pigs in peru have a better diet than majority here in the US. Particularly those on cheap pellets.
Part of what makes guinea pigs so efficient is that they don't need much protein or fat. Poultry feed requires a lot of protein and fat, quail even more than chickens. It's why we can't free range without feeding some type of poultry feed or the laying quality and growth of meat birds goes down. Guinea pigs like other grazing livestock can survive on only plant matter and should only have plant matter. Much cheaper and easier to graze an animal than feed it meat sources. Then when compared to other herbivorous livestock guinea pigs take less food per pound of meat and even if they reproduce slower than other small animals they reproduce much faster than cows or sheep. Rabbits are about the only thing that can compare.
