It will show some value but it isn't going to be better than leadership in a club, or a great LOR from a current employer. The main reason is that med schools want to be certain that you are certain you know what you are getting into. And being that all your ECs are vet related, and vets make less than doctors, you gotta prove you aren't doing it for money. Or because there are far fewer vet schools, it can be argued that it isn't competitive so maybe you can't make it in. There are plenty of reasons, and most of them are stupid. Use your vet stuff to show you have good character and are a dependable person, but get enough ECs to show you know exactly what being a doctor is all about.