The veterinarian costume is a more original slant then dressing up as a doctor or a nurse for Halloween, though the costumes are very similar. However, as a veterinarian is known for caring for animals instead of people, you will need to add a number of different accessories or variations to make this costume really make sense. Fortunately this costume is not very complicated to put together and is an easy one for someone who needs a good costume at the last minute.
Rent, buy or borrow a lab coat that fits, as most veterinarians wear lab coats while they are working. Wear slacks or khaki trousers, as these are more formal and go with how people envision a veterinarian to be dressed. Rent or buy a stethoscope from a costume or props store. Wear this around your neck.
Put a leash and collar on a stuffed animal and drag it behind you throughout the party (though it may get stepped on and destroyed). Alternatively, bring a pet carrier and put your stuffed animal inside of it.
Wear medical gloves and wrap gauze around your pet stuffed animal's body. Have pill bottles with candy in them that you can take and give out to people as a fun Halloween joke.
The more accessories you have and the more realistic your costume looks, the better it will be at the costume party.
If you bring a live pet with you, make sure you can properly care for it throughout the party. If something bad happens to the pet or it becomes scared and you have to take the pet home, it could ruin your night.