Heya, I would suggest having a pup that isnt very protective or defensive cz all you will hear is bark bark bark bark lol. I have a jack russel and he is very vocal down the yard and always wants to run around. I know a few people that have german sheperds and say they are great to have down the yard, I also have a westie and she is really good down the yard but she is 13 now and can't keep up on rides. I hope this helps you though...
Ahh..german shepard I know chases the horses...bites pasterns and what not..i wouldn't suggest them.but I would suggest a border collie.really depends on how you train em.i think border collie would be good for you as far as weight you want.or even a umm........springer spanie.theya re pretty dogs.i have a st.bernard.
Austrailian Shepards are amazing dogs with horses! Also a smaller size good dog is Corgis! They are great. I don't know exactly how heavy they are full grown, but they are amazing. I have a corgi that is 7months old and already knows where she can and cannot be around horses.
In my opinion you can't beat a good labrador. Here is mine...name is Dexter. Don't be afraid of his size. He is an extraoridnarily big labrador. Most are the size you are looking for. Labradors are extremely loyal, very easy to train, and they are not "herders" like the shepheds or collies. Personally I will never own any type of shepherd or collie because their instinct is to chase animals like horses if not really really trained.