The amount and type of experience you need is going to depend somewhat by school. Some schools focus a little more on grades/GRE and some focus a little more on experience, but all of them want you to have a good solid amount of experience. For example, Penn is more of a GPA/GRE school and they want a minimum of 500 hours of veterinary experience. Schools really want to know that A) you are committed to the field and B) you know what you're getting yourself into and you can deal with what it entails.
In general there are two types of experience you'll want: veterinary or animal. Veterinary exerience is done under the supervision of a health professional (generally a veterinarian, although you could also include a licensed wildlife rehabber or a PhD conducting animal research). This could involve anything from shadowing as a passive observer to actually being employed by a clinic or lab. The second type of experience is animal experience, which is not done under a health professional's supervision. Examples could be walking dogs at a shelter, working with/for a farmer, working with a rescue group, working in a pet store, and so on. Taking care of your own animals does not count! There was a thread on here a while ago about the various merits of vet and animal experience, which would have more detail, but you probably want to get some of both.
Schools are also looking for breadth of experience, meaning not just one type of experience. You don't need experience with every type of animal ever, but it should be more than just one or two. For example, I had experience interning under a shelter vet, interning at a wildlife clinic, volunteering with shelter rabbits, and horseback riding (and I was pretty light on experience compared to many on here).
So getting experience is very important, and it can take a while to get your foot in the door so it is good to get started early. Obviously it is a necessary step to getting into vet school, but more importantly it is something that you need to experience to confirm that vet med is for you. There is nothing like coming home covered in blood, iodine, fur, poop, and anal gland secretions and having just had the greatest day ever and wanting to go back for more. I think having that experience is a crucial part of entering vet med and that you should look at it as more of an awesome opportunity to experience your chosen field than a task to be completed. Not trying to put words in your mouth - it's hard to determine tone on the internet - but your post sounded a little like you just wanted to get the minimum in. Anyway there are a lot of good threads on here about how to approach veterinarians asking to shadow and how to start getting experience, so take a look through those too; they have some good advice.
