I have only feed mackerel, never been an avid fish feeder to my dogs, yes they will eat it...but dogs are pigs, they will, or they should eat anything that is put down for them..tinned stuff is full of salt and has too many preservatives. When I have feed mackerel is was fed gut in and head off, and boiled, (I know, I shouldnt)
Vit D is the vit for the absorbsion of calcium, yes cod liver oil does have it, albeit in far less quanity than vit A, there are far better ways to give a dog vit D/D3, my premise has always been more aimed at the dangerous overvitaminisation of vit A, BUT, I may be o