First guinea pigs are not really designed to vomit, so this isn’t something we really see in this species. Furthermore, the material he is bringing up isn’t consistent with gut contents and instead sounds like he is bringing up fluid or mucus from the respiratory tract instead. In regards ***** ***** for that, we’d be most wary of lung based infections but could see this in cases of heart disease (a bigger worry without those airway signs I mentioned).
Now while those are the primary issues here, I have to note that his lack of appetite is just as significant if not more worrisome. This is because this species is not designed to be off food. As I am sure you are aware, appetite loss of can lead to gastric stasis. This is because this species have a more complicated gastrointestinal tract then other domestic pets and if you imagine these guts behave like conveyor belts. They should always be moving, which is why access to slowly digestible foods like hays are fed ad lib.
When a guinea pig starts to goes off their food, for whatever reason (for him likely this heart or lung concern), this can cause their gut to slow or stop, which can lead to gastric stasis, a situation which it is one of the few true guinea pig emergencies. So, if you think he is off food, then it would be prudent for him to be seen by his vet before this can progress any further.
Specifically, we'd want his vet to examine him to address those signs we are seeing. But as well, we'd want them to address the anorexia. Often we'd use pain relief as well as pro-motility drugs, +/- antibiotics. If his signs are severe, he may need to be hospitalized. Or if you are able to provide diligent supportive care at home, they may advise you on how to syringe feed him.
Typically, anorexic cavies need to be hand or syringe fed (usually hourly) to continue nutrition input to meet his body's requirement and keep his guts moving to prevent/address stasis. To support him , Oxbow does make a good Critical Care feed (http://www.oxbowanimalhealth.com/vets/products/critical_care) that most vets will be able to provide this to you. This is a highly nutritious herbivore feed that can be easily made into a slurry for syringe feeding. And it is much easier to use then trying to create a balanced critical care diet at home. That said, for the short term, you can crush his pellets and mix them with Pedialyte or veggie baby food to syringe feed and get more nutrition in.
In regards ***** ***** if he is not drinking or is already dehydrated then the vet might give sterile fluids under his skin. Otherwise, you can try tempting him with pedialyte (fruity flavors are best tolerated) or diluted Gatorade (50% diluted with water). These will help replenish electrolytes and get some glucose into his system. A typical dose for animals is 4.8mls per 100 grams of body weight per day (obviously divided over all day drinking). This is his maintenance rate and it is a good starting place for supporting him against dehydration.
Overall, the signs you have reported are a real worry but not our only one. Therefore, I must advise that he should see his vet as urgently as possible. They will be able to treat him for this, advise you on how to administer critical care diet, and determine the root and cause for this situation. Overall, prompt treatment and supportive care are the best things we can do to get this under control and give this little one the best chance of recovery and getting back to himself.
If you don’t already have an exotics vet, you can find one near you at http://www.aemv.org/vetlist.cfm or http://www.guinealynx.info/vetlist.html. As well, you can check the rabbit vet database too ( http://rabbit.org/vet-listings/ ) as they will also see cavies as well..
Please take care,
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