As usual, I must come to the rescue.
There is indeed a donkey show in Nuevo Laredo, or was a few years ago, the last time I was there. And yes, they will delay the show for a ridiculously long time, so they only have to do it once per night, unless a big crowd demands it sooner... usually not the case.
The show took place in a bar called Martha's. You can go to the obvious forum - Nuevo Laredo - and see Cool Beans map of Boy's Town in a well-marked thread. It even says "Martha's Club, Donkey Show".
The lights will be turned down very low, and the sex is more often sleight of hand - mostly simulated - disguised by the dim ambience.
However, if the current girl is nasty and willing, she will suck the shit out of the donkey's dick, and fuck him if his penis becomes erect.
I haven't seen a donkey with a really good boner, since a human female most likely does not offer the aroma that would trigger that in a donkey (perhaps they could use the piss of a mare in heat)...
But on the other hand, I have seen video in which a shetland pony was fucking the shit out of a woman, very erect and excited, and blows a quart of cum inside her. Which of course falls out of her when horsey withdraws, and plops to the floor. Of course, the woman had to be somewhat of an animal herself to take such a pounding.
You could hear the camera man encouraging her along, telling her to relax so the pony could "find her", in other words locate her vaginal entrance with the head of his cock and shove it in.
I have also seen a woman suck off a horse to orgasm, once in person, a little horse, and several times on video with normal size horses.
On the same topic, I have accidentally run across "dog" videos on the internet, and as a young Navy man visiting Korea, saw a Korean street girl suck a dog's dick for a couple of dollars that a sailor paid her.
I don't recommend for anyone to watch this sort of thing, especially if you're sensitive... you will never get the disgusting images out of your head.
On a related note, if you really like unusual visual spectacles, you can go across the street, just west of the donkey show bar, and pay a couple of transsexuals to let you watch while they suck each other off... at least they're human.
Or, you can just remain an ordinary, innocent, filthy monger of prostitutes, which practically qualifies you for a halo by comparison.
BTW, as far as I know the donkey show in TJ was always a scam. Apparently they take you and show you a piece of shit reel of Mex porn, and when you complain they tell you, "The man in the film is the donkey"... fucking typical Mex bullshit. I heard a lot of San Diego sailors tell that tale, back in the day.