Hi Sophie,
The most common cause of bloat in guinea pigs is intestinal blockage a more rarer cause is gas in the gut. Is your pig off her food and looking uncomfortable?
I find this info online Palpate the stomach and if there is the slightest kind of tightness flick the index finger against the side. If there is a hollow resonance then it is indicative that the problem is air and not fluid. Be certain to differentiate between the two for the treatment for fluid is totally different and if the one is used upon the other it could be fatal. Once you have established that it is air your are dealing with take the following steps immediately. If they are taken early there is a far better chance of success.
Give one tablet Rennie Rapize, crushed and in 2.5ml of water via a syringe. Follow this with one crushed tablet of Buscopan in about 1.5ml water. Leave for about half an hour and then gently massage the sides of the guinea pig, resting it on a towel. Better still if you have access to one of those vibrating pads that are used for people with artritic or circulation problems in human beings, a good twenty minutes settled on it as in photograph should greatly improves the chance of clearing the blockage.
There are a couple of other products that can help if those I have mentioned are not available. Baby gripe water, about three mls, as an alternative to the Rennie, Dentinox collic drops, 1.5 mls instead of liquid paraffin, However, Buscopan, a gut relaxant and analgesic is a vital item in any G.P. medicine cabinet for it can be used with good effect on several other ailments.
You could also ask your vet for advice too.
Good luck!
Louise
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