Cat Food

Dried food is very good for their teeth compared to wet. If they are happy with dried, then I would stick to it...

Mine eats dried quite happily because that's all she's had - although Tesco dried food became a bit of a battle of wills - she refused to eat that one for DAYS and I had to give in, but other than that she'll crunch her way through anything...

Dried food is much better for their teeth, cleaner and doesn't spoil if left out all day, however, it can be boreing, most cats I have had prefer wet food, and serving dried all the time can place a strain on the cats kidneys, likewise a diet of all wet can cause gum problems which are expensive to sort out (been there, visited the vet and paid the bill!!). If you are going to mix fluid with dry food it will spoil as quickly as wet does so IMO you may as well serve canned, I wouldn't add instant gravy to dried as the salt content is ultra high. The OP may be an experienced cat owner but for the benefit of any new Christmas cat owners this is what I do:

I leave dried food out all the time and a bowl of water, I only change the water once a day as cats sense of smell is 40 times stronger than ours and they can be put off by the chemical smell of freshly drawn water and leave it to settle for a few hours. Some cats don't like cold water either and will wait until it is ambient before they drink it. A cat on a wet diet may never drink at all because they gain all the moisture they need from canned food (they are dessert creatures after all) but if you serve dried you must give them water to top up.

Twice a day (brekkie and dinner) I put out a portion of wet food, a portion is enough to eat in one sitting which is about the size of a mouse! If they leave any in the bowl I remove it immediately as I hate the smell and it will spoil within a few hours anyway. Leavings I refridgerate and serve at the next meal. As hunters, some cats will not eat chilled food but in all the years I've owned cats mine have happily tucked into it straight from the fridge.

My aged cat (20yrs) also gets treated to bit of cheese, bits of chicken and other naughties. I wouldn't normally recomend too many non cat foods (WARNING: chocolate is a poison to cats) but at 96 cat years she cannot keep weight on and her age will kill here before a fewtit bits ever will. HTH

What about adding some chopped up sardines and some of the oil they are in to the food?

My two kitties also both only eat dry and seem pretty healthy and happy. When the one had a poolie tummy I was advised to leave him chicken stock as he only wanted water but at least this had some flavour and he loved it. Might be another simple idea. As already said though obviously this should be salt free.

Does the extra oil in the food play havoc with their digestive system - I mean - what are their motions like when going to the toilet. ?

I ask this as I have an 11yr old blue persian, who in the last 10months has been going "off" his back legs, (very wobbly) he's had numerous of blood tests, x-rays etc, and he actually has a problem with the last 3 vertabrate's in his spine. Human version of Spondilosis (sorry not good at spelling this time of the morning). He eats a combined diet of Iams dried & wet food for senior's. Small amounts but on average 4 times through out the day. He is underweight also, not cause I dont feed him properly - this is something which has never been diagnosed. He has a healthy appetite - but can never gain the weight he should be at.

I was wandering if the extra oil, might help his legs/back, but wont cause diahorrea. He's long haired, and can be totally messy if he has an upset stomache

I have 2 other cats, they get fed twice daily, there not fussy eaters, (nor is the persian really) they have a bowl of dried and bowl of wet each Water is always down. Their weight & health are fine. 1 is also 11 and the other is 9.