my dog yelps for no seen reason

Maybe you should call your Vet. He could have some health problem. Maybe change him back to his other food. Maybe he is getting gas pains or not enough vitamins. Good luck with doggy.

If this has happened suddenly, and his behaviour has entirely changed, then i would rush him to the vet, it could be numerous of things. my best guess, would be a paralysis tick, but it could also be he has eaten or consumed some poison, or cleaning product. alot of poisons such as ratsack etc have an ingredient which clots blood, and stops the blood from flowing. Most animals that have had this happen to them, have to be rushed to doctors and have an injection (anticoagulant)and treatment. Some problems, could be since he is 13 years old, he could have hurt his bone, broken one, and torn a muscle, that you dont know about, Dogs are amazing at how they adapt to injuries, but just because they adapt doesnt mean they dont feel the pain, and alot of owners could be clueless about their animals injuries. Other things, could be athritis, but usually that is a more gradual problem. You may want to check his mouth and make sure he hasnt chewed on something, that has gotten stuck in his mouth. I know a dog, that went through this, and he just had tape stuck all around his teeth and down his throat, he couldnt eat or drink much and cried alot. either way the best advice is to get him to a vet. Have them check him out fully. another thing you can do, is do a crt test .. all you do is push your nail against the gum for a second and see how fast it comes back to normal color, it should not take any longer than 1 or 2 seconds. any longer than this, then there is something wrong with his circulatory system. also check the colors of the gums, if they are pale pink, then he is loosing blood somehow.. if they have a blueish tinge, then he is not getting enough oxygen, if they are yellowish tinge, then he might have liver problems, or other related problems. anyway i hope this information helps. I understand this is a very long post and i apologize. :)

It could be Arthritis my sisters 13 year old English Shepard has that, started to do the same thing. Just call the vet, if its arthritis they have a good new suppliment out there that really works. My sisters dog is up and running around again like nothing ever happened.