The debate is simple : can the supernatural ability Entrancement be used in order to control a beast/animal ?
I personaly would say no because the core rulebook speaks about "a person" (which may not be a wild animal) and "mind" (arguably inducing the target must qualify for Mentem spells).
ArM5 p.65 Entrancement also requires verbal communication to command the person.
So I would allow to entrance intelligent animals understanding a language (like familiars or Bjornaer in heartbeast form), but not the average horse: it is not a person, though it might understand a few commands.
Rival Magic p95 mentions "Entrancement can be used against animals if the character also has the Animal Ken Virtue."