Zsuzsa, the blood and mucus is a sign of inflammation in the large intestine (colon), Levi has colitis
. The reason why he strains is because the inflammation gives the sensation as if he has to go. There are lots of many conditions that would cause colitis, it will be difficult for me to determine the exact underlying cause without a hands on examination. But, common causes are: Intestinal parasites, diet, infections, dietary indiscretion, ingestion of a foreign body, or even part of a systemic disease to name a few causes. This is what you can do:
1- Do not give things like Pepto Bismol or imodium.
2- Change diet to rice (50%) and boiled boneless chicken
or ground beef (50%) until the stool is back to normal then wean back into a grain free diet. A diet free of corn, soy, barley, wheat, gluten, casein (dairy), etc. You can check with your local pet store for a grain free diet.
3- Supplement with a probiotic (fortiflora), these are friendly bacterias that help with regularity and inflammation. You can buy this over the counter in any pet store.
4- Consider getting him dewormed, you can buy Panacur (fenbendazole) in some pet stores, online (amazon.com) or vet's office. Give it once a day at label dose for 3 days, repeat after 3 weeks.
5- If after doing the above you do not see improvement within 24-48 hours, have him checked by your family veterinarian. My goal is to provide you with excellent service – if you feel you have gotten anything less, please reply back. I am happy to address follow-up questions. Thank you for your business and I hope to work with you again soon!