Built for scarcity, not for plenty
Donkeys evolved in dry, rocky country where grazing is sparse and poor, and their digestion is tuned to squeeze nourishment out of forage a horse would starve on. A donkey extracts more energy from the same mouthful of hay, needs less of it, and stores the surplus with ruthless efficiency — in fat pads along the neck, back and rump. That is the whole answer to the second half of the question: the donkey is not a scaled-down horse but a different metabolic machine, and feeding him like a horse is the single most common cause of donkey obesity.
The everyday ration: straw, hay and restraint
For a healthy adult donkey at rest, the backbone of the diet is good clean barley or oat straw, available most of the day so his gut keeps moving and his teeth and mind stay busy. Mature, coarse hay can make up part of the ration, especially in cold weather or for old animals, but rich green haylage and young hay push calories he does not need. Grazing time is usually the thing to ration hardest: a few hours on a bare or strip-grazed paddock beats all day on lush pasture. Clean water and a plain salt lick complete the picture — skip horse mineral mixes and vitamin balancers unless a vet advises one for a specific donkey, because his needs are not a horse's needs in miniature.
Where horse habits do real harm
The kindnesses of the horse world are hazards here. A daily bucket of mix or cubes, a net of rich hay to keep him warm, carrots and apples as routine treats — each one lands on an animal designed to thrive on almost nothing. The results creep up quietly: a cresty neck, fat shoulders, then sore feet from laminitis, and in a donkey carrying too much condition, the serious risk of fat mobilising into the bloodstream when he goes off his feed during illness. Treats, if they happen at all, should be a single tiny piece of carrot or a parsnip chip, offered rarely — most donkeys are just as pleased with a scratch and a fuss.
Reading condition on a donkey
Horse condition scoring misleads with donkeys because they lay fat down in different places and can look angular at the hip while carrying dangerous pads on the neck. Learn to feel the neck crest, ribs and rump with your hands rather than judging by eye, and weigh-tape him on a schedule so drift is caught in kilos, not in a crisis. A donkey who is off his feed for a day is never a wait-and-see case: because of that efficient fat storage, an inappetent donkey should be seen by a vet promptly, before fat mobilisation becomes the bigger emergency. When a feeding question remains after those checks, put a follow-up question to KinsLe's Kimmy; she answers using the KinsLe Answers library.