Thank you Anne,
Based on your further history, it does sound like we are facing a infectious process as opposed to benign colonic irritation. Now when we see blood and softer than normal feces, there can be a range of culprits to blame. That said, the fresh blood tells us that we need to focus on conditions of the lower bowel. Specifically, we can see this with anal gland disease (less likely here since both cats sound to be affected and you have not reported either to be painful or having a lump/wound to the side of his rectum), parasitic infection (ie whipworms) and with inflammation +/- infection of the colon (colitis).
In regards XXXXX XXXXX approach here, our first step is typically to worm them. Now I am glad to see that you have wormed them regularly but in this case I would advise double checking that you have used a product that covers whipworms. (Example products would be Panacur, Drontal or Milbemax). As well, if you haven't treated them in the last month, then it would be ideal to do so now. If it has been within the past month, then we can consider whipworms less likely. Just in case you do need to reworm at this stage, I do want to note that the above are typically available over the counter at the vets, pet stores, and some pharmacies. Of course, do make sure you have an idea of their weight before purchasing, so you make sure to get the right dose for their size.
Now if parasites are lower on our differential list, the next step is to rule out inflammatory colitis. This can be idiopathic or potentially low grade bacterial disturbances but can often be settled with a light/easily digestible diet. (Though full blown bacterial induced colitis will often require antibiotic treatment). Examples of bland diets would be boiled chicken, boiled white fish, scrambled eggs (made with water and not milk), or meat baby food (avoid those with garlic powder in the ingredients) There are also veterinary prescription diets that can be used in cases like this (ie Hill’s I/D or Royal Canin’s sensitivity). The easily digestible diet will be better tolerated and absorbed by the compromised gut. We usually will try them on the diet for a week until signs settle, and then slowly weaned back to their normal diet over a week. Further to this, if we do have a GI bacterial microflora upset, then probiotic/prebiotic support (Fast Balance, Fortiflora) can help settle the GI quicker. As well, since you are seeing soft stools, Protexin Pro-Fiber (example) is an over the counter preparation that would support the GI while normalizing the runny feces.
Finally, if you try the above but this doesn't settle in the next 24-48 hours, then you do want to follow up with the vet at that stage. (If you have any doubt that perhaps all the fecal issues are Jerry's and not Tom's; then you can consider separating them with separate litter boxes to determine if one or both is affected). Depending on who the poorly one really is, you can then take that wee lad to see his vet with a fresh fecal sample. The vet will be able to examine him to assess hydration, rule out any anal glands troubles, and get an appreciation of his overall health status. Furthermore, if bacterial colitis is suspected, the fecal sample can be sent to the lab for evaluation to identify the agent responsible and what treatment will be effective to clear it. They can also (or instead) cover him with broad spectrum antibiotics to treat against the most common bacterial agents of colitis.
Overall, we do have a few potential culprits to consider with Tom and Jerry's signs. That said, your history does suggest anal gland issues are less likely and since you have already wormed them, we can hope parasites are less likely as well. Further to this, I would suggest a trial them with an easily digestible diet. If that doesn't settle them in the next day or so, then that would be our cue to follow up with their vet to make sure there is nothing more sinister afoot like a bacterial colitis where antibiotics would be indicated to get them back on track.
I hope this information is helpful.
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All the best,
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