Intact male aggression toward neutered male

Question
I have three German Shepherds.  One year and a half intact male, a spayed 8 year old female, and a neutered 7.5 year old male.  The young intact male becomes aggressive at times (most of the time they get along just fine) with my neutered older male.  The younger male really doesn't become aggressive with my female.  I will be neutering my younger male ASAP, as he just bit my older male who had to have a drain and staples put in.  It was only one puncture wound, and the older male didn't even bother to bite back, but I don't want any repeats of this situation! I just find it odd that the intact male is only aggressive toward the other male even though the other male is neutered.  Is it common for intact male dogs to be aggressive towards neutered male dogs?  It appears to be a pecking order/dominance issue...but how does the intact male seem to know that the other dog is male if it is neutered?  I hope this question makes sense.  Thanks in advance for your input.

Answer
Heather,
We don't think they know the dog is neutered,but they do know it is a male. That is all they need to know. There are still hormones to some degree floating around in the body and dogs don't care if they are big or little, neutered or intact. Just as he knows the one dog is male he can smell that the other one is a female and there is no competition for another female with her. In his mind your older dog is the challenge for her and for the pecking order.

Once they decide there is going to be a challenge to the 'alpha male', which is your older dog, then the challenges might pop up now and then.

Now that doesn't mean that they will continue to fight, because neutering your younger dog will help tremendously. It takes a lot of the why out of the fighting.

So neutering will help, but it might take a few weeks. The older male didn't respond because he has no desire and he is the one challenging.

I hope my answer made sense!