The question is not really that clear, are you looking for work experience to help with regards to your education i.e. hoping to go to University to be a vet or summer work experience, perhaps you dont own a horse yourself and are looking to gain experience by helping out others or is this for extra cash at the weekend?

To any of the above points, if you were looking to ride or work with horses, then it depends if you want to be paid or want to volunter, work experience at a local equine practice would not be paid, there is usually a waiting list, a riding school may offer the opportunity of working for them in return for riding, a local charity would always love willing help, the local hunt yards could be considered. I dont know what else to suggest really, look on local websites and your local tack/feed shop, you never know there may be something of interest for you. Good luck with whatever you find.