My kitty Chorniy got sick with a cold recently and would not eat. I had to syringe feed him for over a week to nurse him back to health. Here's the instructions I wrote up for syringe feeding a sick cat when a member of the Feline Diabetes Message Board when her diabetic cat stopped eating:
First, make sure you TALK TO YOUR Vet. Your kitty might be off food because of something very serious, and you need to know why s/he is not eating. These notes are for those who have talked to their vets and have been told to syringe feed their kitties.
Second, please note that I am not a vet or vet tech. I am a cat owner with some experience in this matter. These notes are meant as a helping hand in a "good samaritan" sense, from one who's been there to those who are going through this angst. Please take these notes TO YOUR VET or go over them on the phone with your vet, to see if the foods I've suggested are appropriate for your pet and if there are any changes to the method of feeding.
Third, you must only syringe feed a cat who is fully conscious and can swallow the food you are going to feed it. Do not syringe cats who are semi-conscious for any reason, whether they are coming out of sedation, having a diabetic low or high, or any other reason.
With that said, here's some notes to help you. Realize that you are not alone... though it might feel like it right now!
Force/syringe feeding isn't cruel. Your kitty may have lost his/her appetite because of an illness, and not eating will make things worse. For example, my cat had an URI (cold), couldn't taste food, and stopped eating. I fed him by syringe for OVER a week. He's eating on his own today, with only a little supplementation this morning. Some cats may take a couple weeks of syringe feeding to get over the hump of a cold or other illness. They might look like death warmed over, just like I do when sick. It's scary.
I've unfortunately had to get good at this. The first kitty I had to syringe feed taught me a lot, and the second went much easier. Here's my various mixes:
Filling food syringes:
Get the 5 or 10 cc syringe either at your vet or at the pharmacy. If you go to the pharmacy, ask for a few of the 5 or 10 cc syringes used for giving liquid medicine to children. They gave me two for free. They need not know it's for a cat, if you think it will make a difference... though why should they care, I buy the insulin there.
You can either take the plunger out and spoon food in the top, or you can put the syringe tip in the food and suck it up by pulling the plunger up. If you spoon food in, when you re-insert the plunger, point the tip of the syringe into a bowl or the sink; food *will* squirt out, sometimes with some force, and you don't want it on the ceiling (it has happened...).
Now you're ready to feed. I kneel with kitty in front of me, his tail between my knees. Grab his head from the top with your thumb and first finger on either side, just at the jaw hinge. Come in from the side, behind the fangs. Try to squirt about 1/2 cc or so at a time. I try to get it on top of the back half of his tongue, so he doesn't flip it back out of his mouth, or dribble it out. But be sure you don't squirt down kitty's throat or s/he might choke.
Caution: there will also be times when the plunger is hard to push. This may mean a bit of food has clogged the tip. Don't unclog it by pushing harder while it's in your kitty's mouth -- it may squirt a lot out suddenly and that will choke kitty. Unclog over the sink, into a bowl, or into a paper towel that you have handy.