I will tell you how I get my cat in the carrier. Like many other cats he dislikes the carrier because he associates it with bad things like going to the vet. Therefore, it is difficult to get him into it. My technique is simple but effective.
Type of carrier
I have one of those cage carriers with the top that opens and the handle is on the top. There’s lots of space to put him in. The whole of the top is open. I don’t have to ‘stuff’ him them through a small, horizontal opening. Many carriers are too small with small side openings. I would recommend my sort of carrier. It is the one at the top of the montage below. Note: if you travel with your cat on aircraft in the passenger cabin, the carrier I have is unsuitable. You might therefore have a ‘vet carrier’ and an ‘aircraft carrier’!
The ambush method
I place the carrier just inside the hallway of my home. It could be another room as the technique is the same. I open the carrier and I then close the door that has access to the hallway or room. The carrier is about two yards inside the door.
I try and make an appointment with my veterinarian at a time which for my cat is the middle of the night. This is the middle of the day for me. He’s a night owl which is typical of domestic cats. This means that he is sleeping or snoozing when the time comes to put him into the carrier.
When that time arrives, I pick him up and walk a few paces only (it should be a short distance) towards the door which has access to the hall. I open the door or push the door open because it might be easier to leave it closed but not on the latch. Right in front of me is the open cat carrier. He sees it but doesn’t have time to resist. I put him in the carrier feet first because, as mentioned, it is a vertical loading cat carrier.
He may put his paws out to the sides of the carrier to resist because he immediately becomes switched on but by then it is too late. He is halfway into the carrier and the deed is done. I close the lid and lock it.
The basis of the success of the system is the ‘ambush’. The whole process of picking him up and placing him in the carrier should be about 5 seconds! He doesn’t have time to recognise the carrier and take evasive action. It all happens too quickly. The fact that he’s sleepy obviously helps because he’s barely awake by the time he’s inside. That’s my technique.
Turning an unpleasant place into something acceptable
Another technique which is recommended by many people is to make the cat carrier a positive or neutral place for your cat rather than a place that has negative connotations.
You can try associating unpleasant objects with positives. You can always leave the carrier open and inside it there should be comfortable bedding and perhaps even a few food treats. You might be lucky and he might go into it as a place to hide or retreat to when he needs some peace and quiet or if he’s a timid cat to hide from an aggressor or some other environmental stress.
The concept behind the second technique is to turn, as mentioned, a negative object into either a neutral one or a positive one. It’s unlikely that he will think it is a positive place but you can neutralise the unpleasantness of it.
My preference is my technique but it does rely, I think, on the type of carrier that you use. My top loading device with the entirety of one side removed provides lots of access and you simply have to drop your cat into it. It always works.
P.S. Obviously, you have to make sure that your cat is around in the home when he is due to go to the vet. And the proximity of his sleeping place to the door behind which is the carrier is pretty important too.