And each year, the association with the box of doom that carries them to their worst nightmare gets worse and worse - to the point where some people are in fact not able to securing their cats and transporting them to the vet and have to resort to calling a vet in for a house visit.
It's a vicious cycle.
And now it is time to learn how to break it and save both of you an enormous amount of stress.
T-Minus Several Months
All right, we'll jump in with the best case scenario. Your cat has several months before that yearly check-up - provided they don't need to take any unscheduled trips. Even if they absolutely despise the carrier, there is room to try things out and do a minimal amount of effort for a maximum amount of pay-off.
First off, consider the cat carrier. How much does your cat hate it? And then ask yourself...how much do you hate it? And then I'm talking interior decoration-wise. You see, the best way of making a cat love their carrier is to turn it into something else that they love. Something that is soft, fun to be in and cozy to sleep in, preferably. So, the easiest solution is to pick a spot where the carrier can stand year round and act as a sleeping spot for your cat. For it to be as attractive as possible, choose a quiet nook that's still in the room where most of the action in the house takes place as that is what most cats will be drawn to.
If you hate the idea of that thing in your living room, consider getting a new one. The association with the new one will also still be up for grabs, instead of the negative association with the old carrier that we need to reverse. While the latter may take longer, it should still be just fine.
Place the carrier in its new spot and add a towel if you can. It will help absorb the cat's own smell, making it that much more cozy and homely to them. Meanwhile, it will act as the one familiar thing they still have when they're being dragged out of their territory, off to the vet.
Keep an eye as to how well your cat is taking to the spot and consider trying different places if you don't get a response after 2 weeks or so. If the deadline is approaching, other tricks can still be used that will be listed below.
The more traumatised your cat has been in the past by the pet carrier, the longer it will be before they actually trust it enough to sleep in - so be patient and use some additional tricks.
T-Minus Several Weeks
So, your reminder from the vet came in and your appointment is in a couple of weeks. All right, time to dust off the old pet carrier or buy a new one and monitor how they take to it within the first few days. Place a towel in the pet carrier or even your own sweater if you don't mind to make it more appealing. Alternatively, try spraying it with some Feliway.
If they don't take to it in a few days, try some of the tricks below.
T-Minus One Week
When you first put it out though, give them an hour or so while you observe how they approach and interact with the box. You know you'll have your work cut out for you when they won't even go near it. Whatever you do, do not panic and force them to take to the box - entice them. Sit down next to the pet carrier and add all the lures listed above. You could quickly pick them up and put them near it so they can check out the goodies but let them walk away if they want to. If need be, use a fishing rod toy to get them to check it out and let down their guard a bit but do NOT stress, force or cajole in any way.
T-Minus 24 Hours
This is less than practical but there are still things you can do. Add their favourite blanket or your sweater or spray the carrier with Feliway (and let it evaporate for about 30 minutes afterwards). Spend an hour or so bribing your kitty in any way you can to at least check out the carrier - and if your cat doesn't get wet food, try putting wet food inside the pet carrier, heated up for 30 seconds in the microwave to really make it enticing.
Watch them check out the box and back off - let them take it in and realise it doesn't have to be a torture box. You're going to be breaking this new built trust soon, unfortunately, but at least they get to wrap their minds about it a little before being forced into it. And after that you have another year hopefully, to make things right.
Catching and crating the cat
However hard this is, tell yourself to calm down. That means actively releasing the tension in your body that your cat is reading like a book. For that matter, eat something. It engages your parasympathetic system which is the opposite of the fight or flight system, relaxing your body and focusing it on digesting. You're not on a mission. The vet is a distant memory that you need to check off at some point. You are a loving owner who wants their kitty to feel safe around them and stop stressing. You want to pet them, reassure them that everything will be ok and pay attention to their needs.
Now communicate this with your body language. Use a high pitched voice and if your cat comes to you when you sit down in the couch, force yourself to sit down in the couch and relax for just two minutes. If they do not approach you, get up and walk towards an object or location near them. Make that your focus. Convince yourself that what you want is that object or location, not the cat. Again, the cat will read your intentions so fool yourself as much as you fool them.
Once you're there, acknowledge their presence, talk to them but do NOT stare at them as you'll give away what you're about to do. Reassure them that it won't be that bad by talking to them or doing the things you would do normally when you're relaxed and engaging them. Do not make sudden movements, however tempting it would be to snatch them. If at all possible, let them come to you. Once you can pet them, you can gently put your hand on the scruff of their neck and secure them. Do not yank, force or in any other way make any scary movements. Just a gentle tug on the scruff will do it. Depending on how jumpy and panicky your cat will be, you'll have to make it a firm but gentle grip without panicking yourself in order to keep them from escaping.
If they are truly panicked and trying to make a break for it, cradle them, if need be with a towel to keep them from scratching you and if they really do not want to go into the box due to panic and you're out of time, lower them into it by putting the carrier with the entrance up towards the ceiling. Gently put them down inside the carrier and block the entrance with your hand to keep them inside as you close the crate. Remember, try to keep your muscles as calm and relaxed as possible so you do not incite more panic which might cause them to force their way passed you.
The more calmly you can do this, the better and the less chance that they'll freak out and escape again. If they do escape, you can do the same procedure again but it will be even harder, both for you and for them as they'll be even less trusting and you'll have even less patience and find it even harder to curb your natural predatory/mission-oriented instincts. So see if you can get it right from the first time.
Once you get back from the vet, make sure that, you start their training in actually loving that pet carrier by following the instructions at the top. It'll make it a lot less fuss and it will reduce the drama when putting them in the box to go for their next trip when they already love that place as their own nest. Hopefully, with some reassuring petting, you will next time be able to just put them inside the box and at best, they might panic a little when you actually close it as that won't be something they're used to. But at that point at least, they'll be safely crated and ready for the vet, meaning the stress will be reduced to an absolute minimum for everyone involved.
And if you really want to go all out, you can even train your kitty to come to you on command, ready to walk into a pet carrier they now love. Fancy that ;)