Like most I put 10 plus years. Public opinion needs to change, or rather public perception needs to change. Most people are pretty ignorant about
this sex, and think only 1 in a million do it. Plus many sincerely believe dogs are 'forced' to do it. That somehow a woman grabs a dog's penis, masturbates it, and then forces it into her vagina (the zoo porno of 20 years ago gave that impression - with dog dildo vids). Whlle female dogs get raped by sex crazy men !
I may be too optimist, but there seems to be slow change in public perception in our favour. More and more bestiality jokes in mainstream entertainment, bestiality sex scandals involving likeable and normal people, and evidence to the public opinion that zoo people treat their dogs lovingly and well, unlike many non zoo people who really treat badly their dogs.
But still in this Trumpian times, with right wing populists running wild also in Europe, such a issue is easy picked up by populists to argue how 'sick' our society is, and only their poltical party will put an end to it.