- one for "closed herd" horses; horses that never leave the farm and never or rarely come into contact with other horses. (4-way, rabies, West Nile)
- one for horses that travel locally and have light exposure to other local horses. Mine fit in to this category now - I have friends haul over to ride with me; and I haul out to ride a variety of places - county wildlife refuge, etc. and my daughter's pony goes to camp with her in the summer. (4-way, rabies, WNV, coggins test, rhino, PHF - I live close enough to the Potomac that it's recommended.)
- one for horses that travel extensively and have contact with horses from outside the locality, ie, any horse with a heavy competition schedule. (These are the horses that get rhino and flu 1 - 4X per year; I'm out of touch of what else is currently recommended for horses with high exposure)
So which category of contact/exposure that you fall into is one of the things you need to take into consideration when you talk to your vet and plan your vaccinations.