Symptoms of low iodine include “spooky” behaviour and depression, hair loss, discoloured patches on skin, and in Bluebelle’s case susceptibility to mastitis and allergies and hunched, stiff “aged” posture. This was quickly and completely reversed by kelp, which had a rejuvenating effect like watering a wilting plant. This was only diagnosed by my habit of reading the excellent Hyperlipid blog of vet Peter Dobromylskyj, who mentioned the symptoms in passing, for which I'm eternally grateful; our vet had drugs for the symptoms but didn’t recognise the cause.
Timing - Bluebelle is fed once a day, in the evening. If she's not interested in food, she's not fed until she asks for it; so every now and then she goes without. She's fed about a pound or more a day; if she asks for more, she'll get it. She might turn up if someone is eating cheese, in which case she'll always be given a bit, and any uneaten or old cheese (cheddar) is given to her.
Illness - it's probably worth giving a little cod liver oil in winter for vitamin D, Bluebelle loves this; just a teaspoon a day.
Parvovirus and distemper are lethal diseases of dogs which are similar to cholera in humans. The dog dies of dehydration, loss of fluids and electrolytes. Dogs can be kept alive till the disease passes (about a week) by force-feeding, twice a day, water and Gastrolyte, or other human "oral rehydration" formula (made up strictly as advised on the packet). I have saved two dogs suffering from parvovirus by this protocol; the dog that received the formula as soon as it became ill suffered no lasting effects, the other dog, which I treated after 3 days, was always a bit skinny afterwards. Another dog that was accidentally taken to the vet and received antibiotics, not rehydration (which a vet could give by IV drip), died there.
I don't know why this isn't widely known.
I'm sure this is a case where many readers will have dogs with unusual dietary needs, or have had experience of deficiencies, diseases and toxins that we can all learn from, so feel free to use the Comments facility. I think my own ideas are working well, but I don't consider them the last word yet.