The ass being tighter than a pussy gives very direct and much more intense feelings. Also, the cum emptying into you gives you a sense of fullness, sort of like a mini enema.
Our sexual organ is the pussy so its obvious that cocks sawing in there gives us raw sexual pleasure. That doesn't mean that anal sex is not pleasurable. Yes, maybe for some it isn't though.
I have been taking objects and human cocks up my ass since a pretty long time before my first ever dog cock there so I guess I was better prepared, atleast mentally.
Preparing, not just for the knot but also the fuck itself is advisable. Be it an enema, buttplug dilatation, lubrication... all are important. Its best if you have a partner to help.
Frankly, if you get enjoyment from vaginal sex, you really don't need to do it back there. It doesn't matter to our breeders. For them it doesn't matter which hole they pound. Till such time as we spread our legs for them, they are happy to oblige us.
If you really want to go for it, please do. You need to be ready for the ride. Take it like a bitch and yes... grit your teeth.
DS