As a personal opinion, I think that imprinting newborn foals is helpful if done in a moderate amount, not full imprinting such as Dr. Robert M. Miller, DVM – who developed the technique – instructs. I have done imprinting on foals myself, and have seen the effects on them. Granted, they are great when you are halter breaking them, but they are entirely too interactive. They can act like big lap dogs. A little respect of humans would be good. I think there can be a happy medium met between imprinting and plain old every day training and interaction with the foal to socialize them properly. It is up to you to decide what degree to implement the training.
If you don’t know much about imprinting, it is a very simple and logical process. By giving stimuli to all parts of the foal’s body, until they relax (or get used to it), you eliminate the fear to be touched there. This way, you can do whatever you need to in that area later on in their life. For example, by putting your finger into their nostrils to moving it around inside, it trains the foal not to be so resistant to invasive procedures such as passing a tube if necessary.
The important thing in imprinting is to not let up if the foal is resisting. If you do, that teaches them that by struggling, they can get away, or get what they want. You want them to learn to submit to you, the human. You need to provide the stimuli until the foal is completely relaxed and just lets you do it. This may get very frustrating when working with a strong willed foal, but you need to be stronger willed.
Another good application is to train them not to spook so easily to certain items such as a plastic bag blowing by. To do this by imprinting, you will rub the foal all over with plastic. You are stimulating various senses – sight, sound, and touch – by rubbing the plastic all over the foal. Using the same application with clippers is a big plus.
Overall, I think that Dr. Miller’s book or video, “Imprint Training” is a great thing to read or see to get a good idea how it is done. You can choose to follow his instructions step by step, or combine parts of it with other training. Any way you use it, I think it is definitely worth some consideration.