My dog went after a chick this morning.

[TrystInn]

We have three dogs who share the yard with our free range chickens. Its never been a problem because the dogs were trained in basic obedience before they were introduced to the birds. We started out with chicks in the brooder in the house, teaching the dogs to leave it, rubbing the chicks on the dogs' faces and heads. Sitting around the house with the dogs and chicks on our laps, etc. And so we had a lot of wonderful moments when the dogs got to be walking brooders, like this:




That''s Flash and he still grooms the chickens! Quite a sight when he grooms our gigantic Cochin rooster, lemme tell you.

Fwiw we have three dogs, all rescues - two basset hounds and a border collie. The bassets are excellent field dogs, we've used them to hunt down racoons and chase varmints off friends' properties. They do not chase our chickens. Or chicks. Or ducks. Or our rabbits. Or our cats. Friends not food.

The border collie is marvelous. She learned to herd with our ducks, now she herds the chickens. Its a bit bizarre but she's wonderful at it. When there's a problem, she lets us know ASAP. She's marvelous with the chicks, very protective especially of the broody mothers. We always know before the eggs hatch, be they under a hen or in the incubator, because Gracie KNOWS and lets us know. She's very bonded to her chickens, it begins early.



Three years and counting, the only bird we've lost was to a Bald Eagle!

 

[nzpouter]

same as all our dogs, all lived free range with all our other animals... and they are fed raw.

 

[dainerra]

training. training. more training. Just like cleaning the coop and scooping poop and all the other jobs that come with having a pet. The only thing more necessary to a dog than training is food!

You already know that he is excited with the chicks. Find the closest distance that the dog first notices the birds in the brooder. This might be in another room if he is one to constantly glance at the door. Put your dog on leash and get some extra special treats that he only gets for this work - bacon, grilled chicken (no spices!), hot dog chunks, etc. When the dog glances toward the birds, say his name and "leave it" If he looks at you, give him a treat - if he doesn't, give a light pop on the leash (think tap on the shoulder). When he looks at you reward him.
You can also teach him "watch me" the same way. You can practice this at random times though out the day. If you have a couple extra minutes while you're watching TV or whatever, just say his name, pause, "watch me" When he makes eye contact, then reward him. You can also (if you get in the habit of keeping a small treat in your pockets) catch him looking towards you say "watch me" and then reward. Or just praise him verbally.

Once the dog is reliably paying attention to you and the birds at a distance, move a little bit closer. If he absolutely blows you off, you're too close. Just back up a bit and begin again. Eventually you will be right amongst the birds. You can then start at a distance or with a long line (20' leash or so) and work from there. I never ever leave my dogs/chickens loose unattended together.
I don't even trust Rayden
I don't mean I constantly hover over the dogs when they are out with the birds, but I am in the area and aware of what they are doing. Think of it as a small child. Even though you've taught them not to play with matches, would you leave them alone in the house with matches scattered all over the floor?

The most important part of the training is to set the dog up to succeed. Don't give him a chance to chase the birds. Don't give him a chance to disobey.

ETA: The best thing about teaching "leave it" is that it works for everything. Drop something on the floor and don't want the dogs to touch it? "leave it" See dog running toward a snake? "leave it" Lots of training and work, but it pays off!
Of course, some dogs just can't be trusted off-leash. Period. They are just too focused on the birds. In that case, just confine the dog when the birds are out.