Guinea pigs, also known as cavies, often turn out to be pregnant even if you thought you were getting two of the same sex or just one female. These little rodents become fertile very early in life, and it's hard to tell their sex when they're young. So it's not uncommon to have a fertile male and female when you wanted two females, or to unknowingly purchase a gal who's already pregnant.
Most rodents and many other mammal mothers build safe, soft, warm nests where they can feed their helpless, hairless, blind young. But most guinea pigs don't build nests for raising babies in. Part of this is because they are born with a full coat and open eyes and are on their feet soon after birth. However, this doesn't mean you shouldn't provide some sort of nesting area for your pregnant sow.
Give Her Space
Give your pregnant guinea pig a personal cage away from the male or cage mate, particularly when she gets closer to delivering. This keeps him away from her food that's been slightly altered for pregnancy and lactation. And it keeps him away from her. Your sow will become fertile again within a couple hours after giving birth, and back-to-back pregnancies would be hard on her body.
Bedding and Environment
Her nesting cage should be clean with soft bedding. Although some wood chips are ideal bedding materials for guinea pigs in general, a softer material such as recycled paper pulp can be more comfortable for her and her pups. Give her a guinea cave or other structure where she can hide and take refuge. The soft bedding and cave will give her areas to build a nest, should she choose to. Clean the cage out and promptly remove bedding where her water bottle drips and from any other damp areas.
General Pregnancy Care
Your pregnant sow is going to get big, sometimes double her normal weight. Even if you normally hold her, resist holding her during pregnancy. Her belly is greatly distended and she's already uncomfortable. She'll need more calcium in her diet, particularly later in the pregnancy and after birthing. If your cavie is older than 7 months, she quite possibly will have a difficult pregnancy because of her pelvis fusing together, so be prepared to get your veterinarian involved.
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