I believe that a foal that has been imprinted will trust you much quicker that one that has not. The imprinting should be done as soon as the colt is born. If you don't imprint within the first few hours, then you efforts may be in vain. I have raised several colts that have been extremely easy to handle and break that were imprinted at birth.
We handle all of our babies from the first couple of hours they are born. I have had great success with starting them. They have been smart, easy to turn and stop, and usually ride right off with out any bucking or rearing. I beleive it is ok to imprint as long as you dont spoil them at the same time!
We've done both. I definitely prefer those that have not been imprinted. The worst horse to train, we ever had, was imprinted at birth. It was a great pet, but very difficult to train. She thought she was a family member, and responded terribly to training. We finally gave up on her and used her as a herd catcher for years. A few years ago we sold her to a petting zoo. She is now 39 years young and gives kids bareback rides in the petting zoo. As long as she can go where she wants she is great, just don't try and redirect her.
I believe in imprinting at birth,I did it with my now 2 year old and he could've cared less when I got on him, the first time. I think alot has to do with the horses disposition also...some are just more easy going than other's. I handled Gun everyday and desensitized him to everything I could think of,he's doing well and seems to have a sensible mind. He trust me so much and is willing to do what I ask of him,he'll be a keeper!!! I have bought and raised babies from 6 months old and handled them alot ...so far I haven't had one buck when I first got on!!! I prefer getting them young and making what I want out of them, and I know everything that has ever been done to them and how they will handle things!!! This is just my opinion for whatever it's worth!!!lol
I have not personally been involved in raising babies, except for a couple of miniatures, so I don't really have any hands-on experience. However, we have friends who have foals every year and definitely believe in imprinting and their babies are always very easy to handle and be around.