Need Help with 8mo Male seems very lethargic after my absence

[nstukan]

Dont know if I am over reacting, but my normally active 88 lb 8.5 mo old GSD pup, "Rocky" seems very lethargic since my business trip. He always loves to play fetch and chase his smaller older Shihtuz housemate. Now he seems to be very mellow and when I just recently played fetch, he would not run as fast as normal, in fact the first time I threw the ball he only jogged and seemed as he was very stiff. He loosend up a little after a few throws, but was not at his normal "active self".
Not sure if my absence and a Change to a different flavor dog food could cause this.

BACKGROUND
I recently returned (on Thursday) from an overseas business trip that lasted two weeks. My wife told me that Rocky seemed depressed and very mellow since my absence. Rocky is my 15 y/o sons dog and sleeps in my sons room every night, so I am surprised about his change of behavior. Rocky is a camping and hiking companion for my son and self. He normally gets regular excersise daily, however since my trip he has done less and less.

Since my return (2 days ago) I've noticed that he is lethargic and only eats once a day. He normally eats 3 cups 2 x a day.
He seems to be slightly taller at the middle of his back and hind quarters than his front quarters. Not sure if this is a growth spurt and could be what is keeping him from wanting to run much.

Three days before my trip I started to feed him the Costco brand Lamb & Rice kibble instead of the costco Chicken & Rice. I read that the Lamb is better than Chicken for the GSD development. He would eat the Lamb, but I had to add a little beef broth to the dry kibble for him to eat it all. He would eat 3 cups 2 x per day before my trip. Since my return he doesn't want to eat it even with the beef broth. I looked online and spoke to my local pet food store and they suggested that it could be the food change and my traveling that could have caused his behavior change. I was also recommended to try a grain free kibble and see if it helps. So I decided to change his food to something better, I bought Call of the Wild Salmon grain free food. I was told that my local police department feeds their GSD's this brand and type with great results for their multiple GSD's.
Rocky ate 3 cups this afternoon, but I needed to hand feed him the 3 cups (I grabbed a hand full of the kibble and he would eat it out of my hand), did not want to eat it from the bowl.

Am I over reacting? Has anyone experienced anything like this with their Pup??

[Jax08]

I would take him to a vet. He could have pano and being very stoic, or he could have something wrong like a tick disease. I doubt it's the dog food unless there is something wrong with it and if it were related to your business trip, he would have brightened back up when you got home.

[nstukan]

Thanks Michelle,
I will take him to the vet later today. He is just such a great pup, I hate seeing him like this.

Nick

[Nigel]

Being lethargic and loss of appetite would be worrying. Perhaps as Michelle said the lethargy could be pano. Also at 8 months, some dogs appetites will start to drop off. I don't if thats what's happening, I would go for a vet visit.

[huntergreen]

is he drinking enough h2o ?