You can train just about any dog at any age. It all depends on the tools you use.
One training tool I will NEVER EVER use are treats to reward good behavior.
When treats are used, what happens when you don't have treats.
You can easily tell a dog that has been trained with treats when seeing them with the owner or handler.
Watch the dog, if it is always looking at the handlers hand or hands, guess where the treats were.
Praise and affection are much better of a reward for obedience and good behavior. Your never without those.
Consistency and repetitive training exercises are by far the most important tasks to master for both owner and dog.
Start with the basics. NO........SIT..........DOWN..........STAY.
You can not expect a dog understand chickens or anything else that matter are off limits if they don't obey the basic commands instantly.
I always use a choker chain to train. The chain needs to be the correct size and used properly.
It must be able to release with no tension applied for it to work. If it doesn't chances are it is on backwards
To correct a dog with a choker chain, simply snap the leash back quickly just to the point of tightening around the dogs neck and then release it.
It is the zzzzziiiiiipppppppp sound of the ring moving on the chain and the feel of the slight tightening around the dogs neck that gets the dog attention and re focuses them.
Correct your dog instantly when they make a mistake.
With practice you will be able to tell they are about loose focus or do something undesirable correct with just a word.
If chain is tight around the dogs throat and / or the dog ever chokes......it is not being used correctly.
It is miss use that caused so many people to think that a choker chain is a cruel way to correct a dogs behavior.
I have never needed to use a shock collar on any of the dozens of dogs i have trained because they know what i say is what they are to do, even when they are out of my reach.
I have a 70lb chocolate lab that i got from a rescue when she was 3. She was a holy terror when i brought her home.
She would chase anything that moved with intent to kill. I worked with her for a week before i would let her out on her own.
I kept my eye on her for the next couple of weeks with only a strong NO to correct the chase / hunt instinct that flair up every once in a while.
Since then i have had no problem with her at all. Cats will literally use her as a rubbing post. She was even adopted by a kitten.
When i got chickens this spring, I had no reservations about letting them free range with her outside unsupervised.
She has been surrounded by the chickens, had them run under her, even pecked with no action taken by the lab.
The chickens actually feel safer with her around and are more adventurous when she is near.