Barley straw (the stalk of the plant after the grain has been harvested) is a great option for this and means they can happily munch for hours on end without gaining weight. a morning and evening 'bucket feed'. You should avoid feeding your donkey any cereals or grains such as oats, barley, wheat and corn (maize). These products are too high in starch and sugar and have been implicated in the development of diseases such as laminitis in donkeys, as well as a leading cause of obesity. Its hard to say specifically how much grass a pair of donkeys needs as grazing can vary so much. Grass should be considered an additional to straw, rather than making up the majority of their diets. Donkeys always need to have something to nibble on so make sure you keep an adequate supply of straw available at all times.   During the winter, when the grass is dead, or at other times of year when there's not enough grass, you can supplement your donkey's diet with meadow hay. This needs to be good quality in terms of being clean, well produced and mould-free, late-cut hay may be better as it is higher in fibre and lower in sugar. Avoid alfalfa unless you have a pregnant or nursing mare, or other special need animals. Make sure it's not old or spoiled, or your donkey could become sick. If you can afford chaff with additives that target hooves, coats, and so on, you may want to investigate the options available. Chaff tends to be suitable for older donkeys with teeth troubles, convalescing donkeys and nursing donkeys.  Be careful not to overfeed your donkey. Donkeys become ill with life-threatening diseases when they eat too much protein and other nutrient-rich food. Donkeys evolved in the arid and semi-arid areas of the Middle East and North Africa, and as a result can get all the nutrients they need from high fibre, scrubby pasture. When grass is too rich or abundant (think dairy or horse pasture), you might have to limit the area available to them to prevent them from eating too much and gaining too much weight. Rigging up a safe, movable electric fence will allow you to portion off the field and restrict the amount they can eat. Move the fence regularly to give them a little bit of fresh grazing. As stated above, donkeys put on weight easily, so be careful with the treats. Give no more than a handful of any treat at a time. Apples, carrots and bananas (skins on) are ideal. Scraps from your kitchen are not a good idea as donkeys will have trouble digesting anything from the brassica family (broccoli, cauliflower etc.), potatoes, onions and many more. Fresh or dried mint leaves make a great treat. Donkeys need a simple, healthy diet and this doesn't include things like toast, biscuits or cakes. Steer clear of highly processed, sugary human and equine snacks for donkeys.  Here are a few supplements your vet may recommend:   An equine specific salt/mineral licking-block may be helpful, but check with your vet first. Chose one that doesn't contain molasses, otherwise they will just be licking the block for the sweet sugar taste. High fibre cubes—may be fed to donkeys needing to gain a little weight, try to find one targeted specifically for donkeys (you may be out of luck here depending where you live), or a second best would be one for good-doers and ponies.     {"smallUrl":"https:\/\/www.wikihow.com\/images\/thumb\/9\/98\/65774-13.jpg\/v4-460px-65774-13.jpg","bigUrl":"\/images\/thumb\/9\/98\/65774-13.jpg\/aid65774-v4-728px-65774-13.jpg","smallWidth":460,"smallHeight":345,"bigWidth":"728","bigHeight":"546","licensing":"<div class=\"mw-parser-output\"><p>License: <a rel=\"nofollow\" class=\"external text\" href=\"https:\/\/creativecommons.org\/licenses\/by-nc-sa\/3.0\/\">Creative Commons<\/a><br>\n<\/p><p><br \/>\n<\/p><\/div>"}  Freeze-dried grass—may be a useful supplement for some ill, underweight donkeys to get them back on form, make sure it is pesticide-free, and never feed a donkey grass clippings as the type of grass may be harmful to the donkey. Be cautious feeding freeze dried grass in any quantity as the high sugar levels could be dangerous to a healthy animal and trigger the painful hoof disease called laminitis. Protein pellets/cubes—these pre-made pellets contain essential nutrients; they're useful for nursing mothers with foals or for donkeys living through very cold winters that might need a boost. Otherwise, this feed is too rich for everyday purposes. Never substitute with pellets meant for a different animal (e.g. poultry pellets); some pellets contain meat and this is poisonous to donkeys. Carrots—what ungulate (hoofed animal) doesn’t love a carrot? Set up a water trough or bucket and keep it full of fresh, unfrozen water at all times. Make sure it doesn't leak onto the floor of the donkey's shelter, since they need a completely dry floor for their hooves. Don’t forget to check in winter to see whether it has frozen over; if it has, you’ll need to clear the ice away, or equip the tank with a heater. Older donkeys will really appreciate a drink of warm water in the winter. Donkeys originated in a desert climate. They prefer warmer weather but are very hardy, provided they are given adequate accommodation. Donkeys do not like wind or rain and will seek shelter from both. Unlike horses, rain seeps into a donkey’s coat and makes life unbearable. The shelter doesn’t need to be elaborate, as long as it is adequate and provides the protection a donkey seeks. A shed, lean-to or barn with hard wooden floors is ideal. Make sure the floors are hard and dry. Donkeys have porous hooves that can become diseased when they stand in wet areas for too long.   In a temperate climate, provide a shelter which consists of a minimum of three walls, with adequate backspace to get out of the rain and wind. This might be a shed, a stable or even a small barn. Put straw on the ground for comfort and warmth, especially in the cooler months of the year. In a climate with severe winter (temperatures below freezing and featuring ice, snow and freezing gales), you must provide a donkey with barn accommodation. The barn should be snug; plug up any gaps that let draughts through to prevent the donkey from catching chills. A winter barn should also have adequate space for exercise, in case the donkey does not like being taken outside at all while snow rests on the ground.  To avoid possible contamination or worm problems, always keep a donkey’s feed area clean. Remove mud, wash food buckets daily and keep hay in a string basket attached to a wall (a hay-net), off the floor. Keep the shelter clean by mucking it out at least every other day to remove the donkey's waste and hay. Spray down the floor and walls and allow them to completely dry out before the donkey uses the shelter again.
Donkeys' main food sources should be low sugar and high fibre. Donkeys need to eat little and often (like other equines) and don't do well if fed large amounts of food in one go i.e. Donkeys are happier with plenty of space to roam around and graze, which they do for the majority of the day. A great alternative to lush pasture is having a dirt paddock, or a non-grazing area, such as a concrete yard, or a sand school. Give appropriate treats. Donkeys are vegetarian and should never be fed anything derived from meat or fish. Check with your vet about dietary supplements; these may be recommended depending on the soil type of your particular region. Provide clean, fresh water. Set up a dry shelter with hard floors. If you chose to put a rug on your donkey for the winter (seriously cold weather, or an elderly/thin donkey) then make sure you take the rug off, check for rubs and replace every day. Keep the feeding area clean.