Is my dog sick or just bad behaved?

[hypnoticarmpit]

Hi, I'm sorry if this is in the wrong forum.

We've had a German shepherd named Chester for around 8 years now and he's ten. Up until recently he was one of the best behaved dogs in the world; he was a big softy who had never tried to hurt anything. He's always accepted my stepfather as his pack leader and has always done what he was told. A month ago we got a new puppy who's very playful and Chester doesn't like it, which is understandable as he's getting old. Whenever the puppy tries to play he growls and bears his teeth bit his behaviour is steadily getting worse. He is growling at my sister"s cats as they try to eat from their own food bowls, he's barging his way into my sister's bedroom in the middle of night and now he is growling my sister and her boyfriend.

And then today! Last week we took in a two year old boxer named Alfie as he was about to be put down. At first Chester was growling and bearing his teeth but after a couple of hours he was fine and was even playing with him. Alfie is extremely timid and submissive to Chester. Today Alfie walked to the kitchen to get a drink from his own water,bowl and Chester locked on to his neck, dragged him halfway across the kitchen and tried to rip his throat out. My boyfriend, my sister and her boyfriend all tried to break up the fight but it took my boyfriend hitting Chester with a sweeping brush to make him let go. He bit alfie hard enough to draw blood and alfie wouldn't even fight back; he went to the toilet all over the floor in fright. Chester has never done anything like this before! He has been around new dogs his whole life as we used to be a foster home for rescued dogs and he has never acted like this!

Also, my sister brought him to go to the toilet the other night and said that Chester was whimpering as he urinated and she thought she seen drops of blood in his urine. Could this be related to his behaviour? (he is being taken to vet for this on Monday btw). Does Chester have a neurological problem, is he sick, or just badly behaved?! Please help, thank you!