Hello & welcome, I am Dr. B, a licensed veterinarian and I would like to help you with your wee one today.
I am sorry to hear Millie is having some trouble passing feces. We can see this be an issue for older cats for a range of reasons. If she is otherwise well and perhaps a bit "lazy," then it is possible that she is suffering with a bit of constipation due to underlying arthritis. We find that some cats with sore jointed will try to put off the strain of squatting in the litter box and by doing so can put them at risk of constipation (since the feces left in the GI becomes even harder).
In this situation, if she is only mildly affected, then your oils may be helpful. That said, both are oils that can be digested by the gut. This means they may not make it far enough down her intestinal tract to aid her passing hard feces in the lower GI and colon. Therefore, if you don't find them working, there are some other tricks you can try at home to relieve her constipation.
First, you can offer some cow milk (not cat milk since that will be lactose-free). Kitties are like little lactose intolerant people, and while the love milk it can move things down the gut a bit quicker (ie. Cause mild diarrhea in an unconstipated cat). If she is mildly constipated, this might just get things moving in the right direction.
You can also treat them with hairball medication (ie. Catalax). This is available from the vet or the pet shop. It works to lubricate the gut (and avoids GI digestion as opposed to the oils) and can facilitate the movement of hard feces out of the rectum. . Alternatively, you can administer a small volume of Miralax (1 tsp per 24 hours), lactulose (LINK) or mineral oil orally (ideally offer in food or if given via oral syringe then take care to avoid aspiration, since that would cause problems we'd best avoid) as a GI lubricant.
Furthermore, if she is eating you can mix in some canned pumpkin or a 1/4t teaspoon of unflavored Metamucil. Just like people, these can restore fecal output regularity. I would offer these with wet food to ease her eating of it, while making sure we are getting water into her (as canned food is 35% water). You also want to encourage your cat to drink as constipation can be complicated by dehydration. Make sure she has fresh water and you can even offer low sodium chicken broth if she won’t drink. If she has recurring issues, these are good steps to also keep her regular.
Otherwise, since constipation can be an early indicator of arthritis starting to bother healthy kitties, I did want to suggest that you may want to try her with glucosamine/chondroitin supplementation. This is a nutrient supplement that is available at your vets, pet shops, and health food stores (as capsules, liquids, and even treats). It works by aiding joint suppleness by helping cartilage replenish itself and blocking enzyme destruction of cartilage in the joint. Often we can find this helpful in animals with arthritis and can sometimes settle arthritis induced constipation. Normally we give kitties 50mg glucosamine + 15mg chondroitin a day per 10 pounds of body weight. So, this would be something to consider for Millie.
Overall, olive oil and fish oils can help lubricate the GI but can only get so far down the intestinal tract before they too are digested. Therefore, these won't harm her, but you may also want to try some of the above with her as well. While you are doing this, I would advise that you continue to monitor fecal output. I would advise trying the above measures, but if you aren't seeing feces in the next 12-24 hours, or she begins to vomit or worsens, then she needs to be evaluated by a vet. Severe impactions of feces are usually secondary to more serious diseases, so if she doesn't respond to our gentle colon cleaning treatments, then she may require more aggressive treatment (ie enemas under sedation).
I hope this information is helpful.
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All the best,
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