Just got around to this thread. Yup, we have a Pyrenees mix. he weighs in at scant 80 pounds. Never bothered the chicken even from day one. He was interested but never did try to mouth them or go chicken bowling. Downside to Pyrenees is that they will bark and bark a lot. Every morning, he goes to the edge of the property perimeter and barks and barks all the way around. He also likes to poop around the perimeter and scatter his poop so coyotes and other predators know not to come into his territory.
Pyrenees is not for everyone. Unless you have experience handling large breed dogs, Pyrenees is definitely NOT for you! Purebreds also have several medical conditions: knee cap problem fairly common and few others that is escaping me at the moment. Pyrenees needs room. If you have a small backyard, forget it. They also do not necessarily make good house pets because they were bred to be LGD of sheep and goats. They also do not do too well in extreme heat owing to their thick fur and undercoat.
And because of their large size, if you can't afford $50.00/month on dog food don't even think about these dogs. Vet bills is pretty expensive and these dogs only live about 10-12 years at most.
So before you decide to go full bore and get a dog bred to be LGD, think long and hard. They need space. They do not make good family pet. And you need to be experienced at handling these large breed dogs. Some will try to be the dominant member of the pack and this includes you. If you let the dog become the alpha, you are in big big trouble. Another breed you want to think twice is Maremma Sheepdog. Beautiful but extremely head strong and will challenge you. Pyrenees male will be around 100 to 120 pound. Maremma Sheepdog is comparable. I think Maremma is harder than Pyrenees to train and handle.
And Pyrenees even though are large will generally do not engage an intruder. They will bark to let you know and they will intimidate the intruder. I'm not sure about Maremma sheepdog.
I get bit peeved when people adopt/buy dogs not suited for their lifestyle and after a year or two dump'em at a shelter or give them to a rescue group. These dogs deserve better than that.
thanks for letting me rant.