A zoosexual/zoophile/bestialist thats sole sexual outlet and attraction is directed toward equine (ie: donky, horse, zebra)
The term 'Exsclusive' can also be added to the description. Meaning that the animal in question is their sole sexual outlet, with no human sexual interaction whatsoever.
Morals are often brought into the argument when comparing these terms and their definitions, but the fact remains that there are people who have done it and people who will do it. A definition exists because the act exists, your choice wether or not you accept it.
"Good freind of mine is an exsclusive equiphile, lives on a ranch with hundreds of horses... Thats got to be one happy camper."