animals mate so that they can procreate and that's it.

Anyone who has actually spent time around animals other than cats or dogs knows this is not true. Monkeys, horses, and dolphins all masturbate, and there are many species of animals that do have sex for reasons other than procreating.

It's possible to raise and kill an animal humanely

True, but the vast majority of food animals are not kept humanely. Surely people are outraged over this, but I rarely see a level of outrage comparable to certain posters in this thread over having sex with them.

And it's not just killing and eating them which animals do not consent to. Animals do not consent to a great number of things, such as being kept in kennels, having their ears and tails docked, or being trained for risky jobs and dying in the line of duty (bomb dogs, police dogs etc) when the animal has absolutely no comprehension of the danger they are being put into for the benefit of humans.

It's not possible to have sex with an animal humanely

Can you explain further? Male dogs and horses will willingly mount females outside of their species, and I'm not just talking about humans either. How does it harm the animal?

Furthermore I'd be interested to know if you or anyone else thinks jacking off a horse into an artificial vagina is rape? Did the horse consent to that?