The Animal Trustees of Austin operate a wellness clinic and one for getting your pet spayed or neutered. While they don't deal with "sick" pets, they do offer a host of services like routine and preventitive care, including vaccinations. The staff is friendly and the vet and vet assistants I dealt with seemed very knowledgeable and had good recommendations. The wait can be long though, so call ahead to find out when they're least busy times are. They accept walk-ins, and I don't think they even take appointments. Still, it's worth it for the quality and service they provide.
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