Aloha! You're speaking with Dr. Michael SalkinSteven, at 16 weeks of age gastrointestinal parasitism is the most common cause of hematochezia - blood in the poo. The nematodes roundworms, hookworms, and whipworms, the sporozoan coccidia, and protozoan Giardia are our primary concerns. You can purchase an over the counter wormer containing fenbendazole (Panacur, generics) which will address the nematodes and the protozoan Giardia. I recommend worming daily for 5 consecutive days. You'll need Ralph's vet to prescribe ponazuril to best address coccidia.It's a good idea to have the vet perform a fecal ova and parasite exam on Ralph's poo if fenbendazole isn't helpful. We'd be looking for parasites resistant to fenbendazole or not susceptible to it at all such as coccidia. Please respond with further questions or concerns if you wish.