Rye,
When the bird's are put under stress, eg :- after race (no later in week than tuesday), on second feed after racing,before and after injections, 2 days before, miss a couple, 2 more day,s, breeding/stock/ moultimg, twice a week.
Natural fresh lemon juice on corn for race bird's or grapefruit juice, then add brewer's yeast.
We also use sunflower oil in the winter months, moulting and breeding.