Thanks for the additional information. It is helpful.
Dogs use their mouths to explore their environment. Therefore everything goes in their mouths. Once they are a bit older, they use their mouths to initiate play with their littermates. They nip or pull or even shake the other puppy as part of play. They tend to do the same thing with their humans and if they have never been taught bite inhibition, it can hurt. In addition, dogs interpret high pitched noises as signs to play and lower toned noises as reprimands saying it is not acceptable. When humans are hurt we frequently give a high pitched noise rather than a low pitched noise. So the first thing to do is adjust your cry when bit to a low toned cry.
Every time he bites, stop all play and if you are not playing, give a NO and a command for something else he can do such as sit. If he hasn't had any obedience training, you need to do that. The following site is helpful in helping owners train their dog. Be sure and click on the link to the page on obedience at the bottom. and links on subsequent pages leading to detailed instructions.
Training works best if you train at least 30 minutes a day (two 15 minute sessions). I would start making your dog work via the Nothing in life is free program (NILF). It is outlined below.
It is often helpful to give the low pitched cry, stop all play and give the dog something appropriate to bite on such as a rubber kong filled with peanut butter that does not contain xylitol or with yogurt. Freeze it first so it will keep the dog occupied for a period of time. Since he seems to do this when he is excited or wants your attention, supply him with regularly scheduled play times. Try to have them at the same time so he knows when to expect his play time. You can play fetch, or tug of war (though I find that can encourage biting like behavior) or kick a larger ball around for the dog to chase after. Any activity to keep him busy and not jumping at your hands to nip.
Along with the play time and obedience training, teach your dog an alternative way to get your attention when he is excited. Some owners teach their dogs a specific treat such as laying down in front of them, or sitting on their rump with their front paws off the ground or other trick. Mine will just sit in front of me to get my attention since their normal posture would be to lay down. If they sit, then I ask them what they want and we go from their depending on the time of day. It might be dinner time or training time or they just want some affection. You should also remember that dogs do not think of obedience training as training or a chore. To them they are getting your undivided attention and they are happy. Many consider it play and will strive to do their best as a result.
Now there are some dogs that just don't seem to get the message. Dogs that are taken away from their mothers too early are deprived of the time with their siblings and other dogs which helps them learn that biting can hurt so they need to be careful. Now there is a method for stubborn biters but it should be used as a last resort. You can stop mouthing and biting hard by going the opposite direction. Instead of taking your hand out of her mouth, put it further in the mouth. DO NOT do this meanly (not that you would). Do not do it quickly or shove it in too far, just move it further in enough that it makes her uncomfortable so that she pulls her mouth away from your hand. SHe will learn that putting her mouth on your hand results in the hand going further in and possibly triggering a gag reflex which she will not find pleasant. I'v found that this methods works on the most stubborn puppies.
These suggestions should take care of your problem.
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