Hello, this is Dr. Bruce and I would like to help you with your kitty.
There could be several causes of the blood and straining. She may be constipated. She may also have colitis (inflammation of the colon) due to infection, parasites or a reaction to eating something she shouldn't have. She may have worms.
If she is still eating, then I would put her on a bland diet for the next 2-3 days. No cat food. Give her only boiled chicken and jars of baby food for her to eat. Make sure that she is drinking enough water. A normal amount of water for a cat is about 1-2 ounces per day. She may need to have water syringed into her mouth to supplement her intake in case she is not taking enough in.
I would also go to the pet store and purchase an over the counter laxative. There are many brands available, so ask at the store. Some brand names are ***** ***** Laxatone. There are several other brands out there. Give her this daily for the next few days. Give a 1 inch strip by mouth. This will help if there is any constipation.
If she is not eating, and is not drinking, then you will need to be more aggressive with the fluid supplementation. Make sure to give her enough fluid to keep her hydrated. However, if the blood continues for more than 24 hours, then she needs to go to her vet for evaluation.
I hope this helps. If you would like to continue this chat, please reply to this post and I will get back to you as soon as possible.
You're very welcome!
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