once uve graduated, u can go and be a large animal vet and work with horses, so technically u are specialising in equine veterinary medicine. But it depends what u mean by specialising, do u want to specialise in a certain equine area, like surgery or cardio etc.
If u want to do something like that then i think u will have to do extra training, this could be a 1 year course, u may be able to train while workin in a practice (like an aprentiship) or u may need to the a specialist equine degree. it all depends on exactly what u want to do.
for instance, i, at the moment am planing on specialising in small animal surgery once i graduate. to do this i want to go work in the queen mother hospital, where i will first do a one year internship (working and learning) in small animal medicine and surgery, i will then do a three year residency in small animal surgery, then if i decide on a particular area of that, cardiovascular for example, i will specialise in that.
so really there is no real set route, thats why being a vet is such a good career, you have soooooo many options upon graduating. dont worry bout it tho, you have plenty time to decide, u dont have to do anything specific until uve finished uni to specialise. you may well change ur mind when u get to uni, u might find something else which u really really love.
hope this helps a bit,
cya