Hi,feeding your birds all that fat sounds like a good way of stopping your birds from laying to me,they will put on a thick layer of fat around there internal organs and vent and will not be able to pass an egg.
Fat is good in the winter for little blue tits that have to work hard flapping there wings searching for food through ice and snow ,but very bad for a lazy old chicken who spend much of its time over the winter sitting in its coop sheltering from the weather with a crop full of pellets.
Graham.