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A pup's stomach will often appear a little bloated and hard especially after they eat. In addition, puppies this age frequently have parasites like worms which can also cause a bloated and hard abdomen. I'd suggest you at least get him dewormed. For additional information about worms, see this site
Common dewormers are Panacur, which is a prescription product so you need to obtain it from your Vet and it works on roundworms and whipworms. Wormers labeled as Pyrantel Pamoate are the best over the counter medication for roundworms. Drontal plus is also a prescription product and is used for the treatment of Tapeworms, though dewormers with praziquantel work well against tapeworms. Many heartworm preventatives also help control whipworms and roundworms. Another reason to keep your dog on Heartworm medication.
He will need to be dewormed at least twice, preferably 2 weeks apart to kill all adult worms and then any hatching worms before they can reproduce.
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