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Provide extruded pelleted feed. Provide clean water at all times. Provide quality hay. Offer fresh vegetables every day. Ensure you’re providing enough vitamins and minerals. Increase the amount of fruit you provide in the last 4weeks of pregnancy.
In a pellet feed, each chunk of kibble is identical. Choosing pellets over muesli (where you can identify individual peas, corn, wheat etc.) prevents selective feeding. Do not over-feed pellets as too much can cause the guinea pig to become overweight. Read the packet for how much, but it should be no more than a few teaspoons or a dessert spoon a day.  Selective feeding is where the guinea pig chooses the tastier bits of food over less tasty – but often more nutritious – foods. This causes mineral deficiency. If you are changing the feed, make a gradual change providing a bit of both to start with as otherwise she may not eat the feed at all. All guinea pigs should always have access to clean water, but this is even more important when they are pregnant. Empty the water bottle and re-fill daily, to ensure the water is clean.  If the water bottle is usually placed high-up, provide a second water bottle lower down so that the sow does not have to stretch if she does not want to. Clean the water bottle weekly to prevent the build-up of algae and bacteria. Wash out the water bottle with a gentle dish soap every few days. Provide grass hay (timothy or orchard) with a green tinge. Supplement this with a daily dose of alfalfa hay which is higher in protein and calcium. Make sure hay is freely available at all times, and provide in a large ball the guinea pig can burrow in. Alfalfa hay is great for pregnant, nursing and young guinea pigs but the calcium content is too high for normal guinea pigs as a build-up of calcium can cause bladder stones. All guinea pigs should be given at least one cup of fresh vegetables a day, but as the pregnant sow begins to eat more you can increase this to 1½ to 2 cups a day. For which vegetables are suitable, see Care for Guinea Pigs. Never offer the same vegetable two days running. This prevents an excess of one particular mineral that might be contained in that vegetable. For example, carrots contain lots of oxalate. If your pet has too much of this, it can build up in urine and cause bladder stones. Pregnant guinea pigs are vulnerable to vitamin C deficiency and calcium deficiency. Ensure you are providing enough of these by using a supplement such as Oxbow Natural Science Vitamin C or a similar product.  Never provide a multi-vitamin. Excess vitamin C is passed in the urine so can’t be over-dosed, but other vitamins can build up and create problems. Do not rely on foods that list added Vitamin C as an ingredient. Vitamin C is highly unstable and breaks down within 8 weeks of the manufacturing date. If the food has been stored for a while at the retail outlet, the chances are the vitamin C content is already negligible by the time you open the bag. Never use a water-soluble tablet. They become ineffective quickly and may put the sow off the water, leading to dehydration which could be fatal during pregnancy. Give a small cube of fruit such as apple, strawberry or seedless grape every 3 days. Fruits should usually be given sparingly to guinea pigs because the acid can give them mouth ulcers. However, toxemia is in part a lack of sugar, so keeping sugar levels high is important.