Except for hay, dry food should never replace fresh food in a diet for guinea pigs. It may only be an addition in case the guinea pigs are ill and need to gain weight and to receive more vitamins and minerals.
The most important dry food for guinea pigs is hay. Since hay is crucial for their digestion, guinea pigs must be supplied with enough hay all day long. Their digestion needs food non-stop and hay is the only food that may be eaten in such a huge amount. Hay also containts a lot of vital minerals and vitamins and is important for maintaining guinea pigs’ teeth. The molars in particular wear down 2mm / 0.079 inches every week only by chewing hay. Pet shops sell hay with a lot of different herbs in it but it doesn’t really matter which herbs are enclosed. The hay should always be stored in a dark, dry place to avoid mould.
Apart from hay, every other dry food as well as pellets should be regarded as concentrate feed. Most sorts of dry food sold in pet shops contain way too much sugar and fat and thus healthy guinea pigs should never get this kind of dry food. Feeding guinea pigs fresh food combined with hay is perfectly fine and giving them too much dry food will even make them obese quickly.
Guinea pigs love old bread and rusk. Nevertheless, it should not be fed to them too often, as it makes the guinea pigs feel full too quickly, causing them to eat less hay, therefore harming their teeth and digestion.
Various salt licks and mineral licks are available in pet shops but guinea pigs receive sufficient salt and minerals through fresh food and especially through hay. Therefore these licks are not required and can even damage the guinea pigs’ health if they get too much salt or minerals.
Giving the guinea pigs additional vitamins is also unnecessary, as a well fed guinea pig gets enough vitamins from its fresh food.