Critical Care is a specially formulated handfeeding food for guinea pigs who can't eat. However, while you are sourcing that, you can give him pellet mash.
Pellet mash can be made by soaking some pellets in warm water and when softened mashing them with a fork until smooth, you're looking for the consistency of toothpaste. Don't make it too runny, this can be a higher risk of aspiration, which is when some food accidentally gets in the lungs. A lot of members here have had great success mixing some canned pumpkin into the critical care, which is high in fibre and will help keep his gut moving. it is essential he eats, and regularly, to avoid GI stasis.
He needs to get 120ml of food minimum every 24 hours. He needs to be fed every three hours. Day and night.
You can use a 1CC syringe to feed him, cut the tip off to make the opening wider and file down to smooth down any rough edges. Or you can use a 30ml syringe with the narrower tip, but be careful not to press the plunger too hard, as this will come out very fast.
To feed him, you can gently wrap him in a towel to make him comfortable and keep him still, popping him in a lap or on a flat surface will make it easier for you both.
Slip the syringe down the side of his mouth, making sure you get it well behind his front teeth. You want to get it all the way to his back teeth. You will know when you've achieved this because he will start chewing. When he starts chewing, begin slowly syringing him food. Their mouth can hold between 0.3 and 0.5ml food at a time, so make sure you give him the syringe bit by bit and pause in depressing the plunger to let him chew and swallow. However, try to avoid taking the syringe out his mouth until it is empty. This will make the process easier for you both and less stressful. If he is chewing then he is swallowing.
You need to get as -much- food into him as you possibly can. I would say at least 15ml per sitting. If you cannot do this much in one go, you will need to do smaller feeds more often.
If you have never done this before, it helps to have two people do it, one to hold piggy and one to syringe.
If you find he is resistant to having the syringe put in his mouth, a very gentle thumb and forefinger over his snout with pads of thumb and forefinger resting on both cheeks will allow you to carefully maneuver his mouth open and help keep him still.
In between syringes of paste, still offer him normal food. You do want to encourage him to eat on his own. Little bits of veggie or fresh grass (providing it's clean and pesticide free).
He also needs to be syringed water. Use the same technique as the food, but do this -very- slowly. You can do this in between syringes of slurry to help hydrate him. Even better, if you can get unflavored pedialyte, make some up for him, for hydration purposes and syringe this. Most pigs like this very much and will take the syringe willingly.
I cannot stress how important it is to do this regularly. Day and night. no exceptions. You have to keep food moving through his gut. remember, it is slow, take your time. Try to remain calm as a first time syringe feeding can be daunting. But you must do this for him. If you haven't already, you need to start immediately.
