zootech, I probably should have been more clear. People on these frums aren't down on breeders because of the purebred issue (which doesn't really affect guinea pigs since there's no temperament or breed traits other than appearances.) The beef is more with actual breeding practices.
Pregnancy is always a risk for female guinea pigs. Accidental pregnancy is one thing, but deliberately endangering female pigs is another. It does not help that for whatever reason, many breeders do not follow basic care standards, increasing the risk for health problems. As you learned, even a reputable breeder can have a parasite infestation in an infant herd. Other breeders sell stock to pet stores or cull for showing. Many breeders are ignorant of proper guinea pig care, and it does not help that they contribute to the overpopulation problem.
On the rare occasion there is a breeder who wants the best for their piggies and does take good care of them, but rescues tend to have run ins with more bad than the good. Maybe if breeders caused less problems for rescues, some people would be more open to them. But to many people, breeding deliberately is in itself an unconscionable risk to the sow.
So, it's not anti-purebred prejudice. It's more about breeding practices and how they contribute to the sick guinea pig overpopulation problem--while other guinea pigs languish in the shelter and are put down for being unwanted. And until breeders follow care standards to prevent disease transmission, it is always wise to quarentine!
She's nuts. She even got mad at me because I told her onions were bad for piggies. Apparently, she feeds it occasionally to her pigs and they "have not died from it yet!!" Not that she bothers to actually figure out what was wrong when her guineas dies...I'm sorry you had such a lousy experience, Kaylee. This person sounds particularly clueless.
Anyway, from an article in "Veterinary Technician" - http://www.aspcapro.org/animal-poison-control/documents/x-vettech_0801.pdf :
Of large animals, cattle are the most susceptible to onion toxicity. Horses are not as susceptible, and sheep and goats are somewhat resistant. In areas where onions are grown commercially, sheep may be fed cull onions (deemed unfit for human consumption) free choice without experiencing toxicity; for cattle, ingestion of more than 25% of their diet as onions may be hazardous.1 While it does not explain the relative resistance of sheep and goats, the oxidative threat to cattle is greater because onions also contain S-methylcysteine sulfoxide (SMCO). SMCO is metabolized in the rumen, producing dimethyl disulfide, another oxidant. Because SMCO is absorbed in the intestine and not converted to dimethyl disulfide, it does not affect nonruminants, including hindgut fermentors (e.g., rabbits, guinea pigs, horses).1
Nonetheless, I still won't be feeding my guinea pigs leeks, chives, garlic or onions.