Hello & welcome, I am Dr. B, a licensed veterinarian and I would like to help you with your wee one today.
If Marshmallow has had diarrhea since you took her, then we do have to consider a chronic issue afoot. And while GI worms are a common issue for young kittens, they are by far not the only potential suspect here. Other agents that could give a kitten chronic soft feces or diarrhea include bacteria, viruses (coronavirus, rotavirus, panleukopenia, etc), parasites (GI worms but also the protozoa like coccidia, giardia and also cryptosporidia, tritrichomonas), nutritional sensitivities, stress, and toxins (this last one less likely in this situation).
Now I am very glad to see that you have properly wormed her even though there was a possible history of worming. This way you know it was done and can rule out GI worms at this stage. From here, the next step is to rule out dietary sensitivities and try to offset fecal losses (since diarrhea will cause fluid and nutrition losses that can lead to dehydration and stunting). In regards XXXXX XXXXX you can consider a trial on a light/easily digestible diet. Examples of this would be boiled chicken, boiled white fish, scrambled eggs (made with water and not milk), meat baby food (do avoid the ones with garlic powder in the ingredients) or there are also veterinary prescription diets that can be used in cases like Hill’s I/D (LINK) or Royal Canin Sensitivity Control (LINK). The easily digestible diets tends to be better tolerated and absorbed by the compromised gut. And even if a infectious agent is wrecking havoc on her GI, then we want to be making her ability to gain nutrients as easy as possible for the gut. Furthermore, if we can aid the gut in taking up more of the nutrients she is ingesting, we will also see less diarrhea as a side effect. So, consider offering these for the next week or so, and do so in small frequent meals, as this will again lessen GI strain and reduce diarrhea.
Further to this, I would note that you could consider supporting her compromised GI microflora (the good bacteria) with a pre/probiotic treatment. These can be very helpful in chronic diarrhea cases where the gut bacterial load is in severe imbalance. There are a number of options on the market but the one I tend to use for patients is Purina Fortiflora. Alternatively, you could consider Protexin Prokolin. This product is available OTC at the vets and contains a pre/probiotic and a small volume of a feline safe antidiarrheal agent to slow her runny feces. Now in mentioning anti-diarrheal agents, I do want to warn you to be cautious with these. I would not advise using any other product safe for the one I noted (which is very mild). The reason is because some of the bacteria (with endotoxins) and viruses that we have to suspect could actually cause her more harm if they were allowed to remain in the GI longer then they may be at the moment (where the body uses diarrhea to flush them out). So, until we knew exactly agent is presnt, we'd not want to give any other stronger anti-diarrheals (not to mention some human ones are not safe for kitties).
If worming, a bland diet, and GI microflora support don't settle her diarrhea down, then we's need to consider involving the vet to rule out those other causes for this chronic diarrhea presentation. And if you do have to go down that route, then a fresh fecal sample can be key to helping you determine the underlying cause for her diarrhea. Ideally, we'd want to have the sample sent to the lab for examination and culture. The lab will be able to rule out parasites, protozoa, test for viruses and culture the feces for pathogenic bacteria. This enables us to isolate the causative agent and use targeted treatment to clear it for her. So, this would be the next step if benign causes like worms and diet sensitivities are ruled out for Marshmallow.
Overall, in Marshmallow's case, it sounds like we have a chronic agent that has been causing diarrhea for a wee while. Therefore, we want to take a step by step approach to determine the cause and address it. You have already taken a good first step but if she hasn't responded then we do have to look past the worms. Therefore, do try her on an easily digestible diet and if she doesn't settle within a few days, then consider having your vet examine her at that stage and have them send off a fecal sample. This will allow you to pinpoint the cause of the diarrhea, and the vet will be able to cover her with the appropriate treatment to settle her diarrhea once and for all.
I hope this information is helpful.
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All the best,
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