Animals are equipped with fat not only for energy storage, but also for regulation of body temperature and as a source of many hormones. It is reasonable that animals eat and store fat based on physiological demands.
Why do animals need fats and oils?
Animals generally either store absorbed fatty acids or oxidize them immediately as a source of energy. Particular fatty acids are needed for the production of phospholipids, which form an essential portion of cell membranes and nerve fibres, and for the synthesis of certain hormones.
Why do cows need fat in their diet?
With most animal feed, fats are released into the rumen and can cause an oil 'slick' that coats the fibre in the rumen and prevents rumen bacteria from breaking it down. Your dairy cows may require over 6% fat in dry matter to maintain their body condition and productivity.