I'll point out that bestiality porn is illegal in the US and most other countries. If you're watching this then you either possess or are accessing illegal material. While you can find pretty much anything on the internet, you don't find bestiality porn without actively trying to look for it, meaning you've gone out of your way to find videos of people having sex with animals. That doesn't speak highly about you since you also claim to think it's wrong or at least "against nature."
As to your specific question, yes, the animals are trained to have sex with people. This would be considered animal abuse in most countries and would land you in jail. Prison inmates are notoriously intolerant of pedophiles and any other offense that's deemed sexually perverted (although not adult rape, oddly), so if you're arrested for this you can look forward to lots of violence and sexual assault directed towards you while you are incarcerated.