Hello & welcome, Liz. I am Dr. B, a licensed veterinarian and I would like to help you with your wee one today.
Based on your history, it does sound like Bertie has a few different issues afoot. Now I can certainly address the supplements for his coat and advise you on some supplements that could help with his very likely arthritis. Still I would note that we need to keep a close eye on this weight loss. If his bloods were all normal, then we'd have to be a wee bit concerned that the weight loss could be due to decreased food intake (secondary to bad teeth) but could also be due to other underlying health issues. And while I hate to even mention it, weight loss where all systemic/metabolic/organ issues has been ruled out does raise concerns about possible tumors (since they often steal nutrition with little other sign of issue). So, this needs to be considered with his weight loss and if he is still actively losing weight, then this could have a knock on effect with his coat (since the body will be re-routing what nutrition it is getting to more critical organs).
Now in regards ***** ***** and coat health, when it lapses we often need to consider essential fatty acid (EFA) supplementation with him. EFA’s are the fats that are part of skin cells composition and play a role in their health and coat growth. They are often used therapeutically in the management of a number of feline skin disorders.
A general recommendation for dietary supplementation with essential fatty acids is based on supplying 1.5-2.5 ml fish oil for a 4kg cat. Alternatively, you can offer a small volume of fresh salmon weekly. Alternatively, if he isn't keen on fish, then there are alternatives that you can get OTC from a vet or even order online. Examples of oral EFA supplements include Viacutin (LINK) or Yumega (LINK).
Turning out attentions to his elderly joints, there are also long term supportive treatments that can be helpful with arthritis in cats. First, since its always grand to hit two issues at the same time, we actually find that fish oil (omega 3 or 6; EPA/DHA) can help joints just as much as the skin. Furthermore, it can act as a light hair ball treatment for te upper GI to help reduce that for him as well. In regards ***** ***** oil, these can be helpful for joints as they do have anti-inflammatory properties. In regards ***** ***** we tend to give this at a rate of 20mg per pound of their body weight. And this could just help soothe any joint inflammation and be a long term management option with his arthritis.
Furthermore, you can use glucosamine/chondroitin with your wee one. These are a nutrient supplement that is available at your vets, pet shops, and health food stores (as as capsules, liquids, and even treats). They work to aid 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 mild signs and this could just take some of the discomfort away from him. Normally we give kitties 50mg glucosamine + 15mg chondroitin a day per 10 pounds of body weight. So, these would be worth consideration here as well.
Overall, Bertie does sound to have a few lurking issues. We can address the coat and help his joints with the above. Your metal comb is fine to use as it will cause no harm. That all said, I would again note that we do need to monitor his weight and his appetite (as you are). If he is struggling to eat, consider pate style kitten food (which is easier to eat and has more nutrition per bite) or supplementing with a calorically dense diet like
Hill's A/D (LINK), Royal Canin Recovery (LINK), or Clinicare Canine/Feline Liquid Diet (LINK) to keep the weight on. But if he is eating well and continuing to lose, then we do have that concern for his health. And in that case, it will be a situation where you could test or just plan to keep him as comfortable as possible for as long as possible.
I hope this information is helpful.
If you need any additional information, do not hesitate to ask!
All the best,