ive had stock birds in for a few years partly because of the rules and regulations where i stay, and recently said ,to pot with it im letting them out as i hated keeping them in, i now see a differnce in thes birds , ie condition contentment etc, but can really understand your problem , its really a lot of work cut out for you ,,and difficult to put priority to the birds that are not racing , but really think it would pay dividends if you could manage them out , if not every day, as many times that are possible , i see your also racing natural birds , would it not be possible to exercise your naturals on their own and after theve had their fly let the stockbirds out with these after a while you may even get another fly from the birds as the stock birds get fitter, but i do realize how hard it is to fit all this in ,,,but theres no doubt about it the stockbirds will keep better, breed better ybs , if you can get them out to let them for a little fly pick some natural minerals etc, but very hard work so wish you well :)