Donkey Nutrition

New research confirms that donkeys have different
dietary needs that horses & ponies.

By Eduardo Valdes, PhD

The Adaptable Donkey
Feral donkeys are highly adaptable herbivores that consume a variety of grasses by browsing and foraging to obtain their required nutrients. The modern donkey is believed to be a descendant of the Nubian and Somali wild ass from northeastern Africa and evolved in a hot semi-arid environment. As such, donkeys are users of low quality, high fiber food and are able to withstand heat and dehydration. Their unique morphological and physiological adaptations allow them to utilize foods that related species (such as the horse) cannot. In addition they are able to survive harsh environments with very low food abundance or quality. Similar to the horse, the digestive system of the donkey is adapted for both grazing and browsing. The relatively narrow muzzle of the donkey as compared to the horse indicates a more selective feeding strategy. However, depending on the quality of the feed, donkeys will use different feeding strategies. They will use a selective feeding strategy targeting high quality bites when foraging over a mixed pasture, but will maximize intake when fed homogeneous hay. In addition to different feeding strategies, research has shown that superior forage utilization in donkeys can be attributed to lower daily water requirements and more efficient recycling of blood urea. Certainly the nutritional needs of donkeys will depend on many factors including breed, genetics, physiologic stage (growth, pregnancy, lactation, work), illness, environmental conditions (temperature), size and others.

Dry Matter Intake
Researchers have found that when donkeys and ponies are fed moderate or poor quality forage diets, donkeys consumed less dry matter per day and showed higher digestibility coefficients of the organic matter, acid detergent fiber and neutral detergent fiber. However, differences in dry matter intake between donkeys and ponies appear to depend on the quality of the forage fed. Reports on voluntary dry matter intake in donkeys range between 0.83 to 3% of body weight (BW). In Mediterranean miniature donkeys fed at 1.5% of BW using diets high in grass hay (98 % Coastal Bermuda grass) and low in pelleted feed (2%) normal health status was maintained. Mules (cross between a jack and a mare), unlike the horse can be self-fed with safety. If mules are offered free choice forage, concentrate and water, animals will not over eat or over drink whereas horses typically will over eat or over drink with the potential medical consequences (colic).

Mineral blocks should be provided at all times to donkeys and other equines.

Nutrient Digestibility
Studies have shown that digestibility coefficients of the main dietary components of forages measured in donkeys were higher than those measured when the same feeds were fed to ponies and horses. This difference is even greater for low quality forages. It has been suggested that because of the differences in the ways in which donkeys and ponies consume and digest feeds, the donkey cannot be regarded as a small horse when considering its nutrition. Donkeys have more similarities to cattle than ponies with regards to forage. Moreover, efficiency and forage digestibility in the donkey approaches that of the Bedouin goat.

It has been reported however, that mean retention time of alfalfa and straw type diets is shorter in donkeys than in Bedouin goats, consistent with a capacity to compensate for lower quality diet by increased intake rate compared to other equids, however, many authors have found that donkeys show slower rates of passage for a variety of diets. Reports indicate that a more effective microbial digestion in the hindgut of the donkey compared to the pony may account for the higher digestibility coefficients. Higher volatile fatty acids production in the hindgut and higher cellulolytic activity in the cecum of donkeys have been reported.

Energy
Indicated by studies, the donkey’s resting metabolism is 20% lower than that of a horse. Furthermore, it has been suggested that the energy requirements of donkeys are in the order of 75% of those published for horses. In terms of digestible energy (DE) requirements for donkeys fed a hay/straw mixed diet, donkeys required considerably less DE intake than ponies to satisfy their maintenance requirements. When equations developed for horses have been applied to estimate DE requirements of donkeys, these equations in general have overestimated (34 -51%) their DE requirements. For miniature donkeys with an approximate body weight of 110 kg, an NRC modified equation has been suggested to calculate their maintenance DE requirements (DE Mcal/day = 0.61+ 00.3 x BW, where BW = body weight in kg).The donkey seems to have a lower energy cost of walking and work per unit live weight, compared to other animals commonly used for work (horse, ox and buffalo). Thus, reports indicated that energy cost of walking donkeys and ponies was 54 % and 50 % lower, respectively than in cattle. Unlike donkeys in the USA, donkeys in the Mediterranean region and Africa are numerous and play an important role in the regions’ rural domestic economy. Despite its small frame-size when compared with cattle, the donkey is considered the most efficient power unit in agriculture and is the reason why donkeys are traditionally used for transport and lighter tillage operations in some parts of the world. Some researchers have demonstrated that calculations based on the metabolic live weight, work output of donkeys pulling a load is higher than that of cattle doing similar work.

Protein
Early work indicated that donkeys can utilize protein very efficiently. Donkeys can re-absorb up to 80% of the urea filtered by the kidneys when fed a wheat straw diet. The efficient utilization of dietary protein, a high true nitrogen digestibility, and the high capacity to retain and recycle urea creates the ability for the donkey to subsist in low-protein forage areas. Researchers have suggested that crude protein (CP) requirements of donkeys are low, falling between 3 – 8 % of the diet. Miniature donkeys can be maintained on diets containing 8% crude protein or approximately 1.2 g CP/kg BW (130 g protein/day). The equation developed for horses can be applied with caution to determine the maintenance crude protein requirements in donkeys (BW x 1.26 g/kg BW/day).

Water Intake
Donkeys have lower water requirements per unit of body weight than other domesticated animals (horse included) with the exception of camels. They can conserve body water and avoid thirst by reducing sweating for thermoregulation and reduced fecal water loss. The amount of water consumed is influenced by the environmental temperature and humidity, the type of feed being consumed, the physiological status of the animal and the amount of work. Studies indicate that donkeys can drink up to 9% of BW per day under high ambient temperature compared to 4-5 % of BW/day in temperate regions, independent of the amount of feed offered. Donkeys can withstand up to 25 % weight loss due to dehydration and recover the loss when water is available. Donkeys normally will not over drink water after being dehydrated, unlike ponies that when offered water under a similar situation can over compensate for a water deficit previously incurred.

In North America, from spring to early fall, in a normal year (e.g. precipitation), pasture can provide enough nutrients to meet the donkey’s needs. In the fall when pastures are depleted and during the winter months, the diet may consist of good quality grass hay supplemented with a pelleted feed. The pelleted feeds or concentrates will ideally have low levels of total soluble carbohydrates (non-structural carbohydrates, NSC), including low starch levels with a protein level of 10 – 12 percent and should be fed according to the donkey’s body condition. However, concentrate feeds such as grains are seldom needed by donkeys, although whole oats, rolled oats and rolled barley are common feeds fed to donkeys in North America. Legume hay (alfalfa) is not recommended for donkeys because of its high protein and digestible energy levels, although mixed legume-grass hays might be used in donkey feeding programs. For example, a 50: 50 percent Timothy : alfalfa hay is suitable for donkeys that are growing, pregnant, lactating Jennets or in some geographical locations where winters are harsh. If pelleted feed is included in the feeding program, a general guideline to feed donkeys is to offer a total weight of hay and pelleted feed of 1 kg (approximately 2 lb) per 50 kg (100 lb) of body weight daily to satisfy their maintenance requirements. Miniature donkeys can satisfy their nutritional maintenance requirements using less total food at a level of 1.5 % of body weight (0.75 kg hay plus pelleted feed) per 50 kg of body weight. Forage should constitute the majority and up to 95-98% of the total diet. Certainly in animals subjected to work the total amount of feed offered will increase slightly and the ratio of forage to pelleted feed will change as well. The changes will ultimately depend on the body condition of the animals and how much the donkeys are required to work. For example a 200 kg donkey at rest can be offered between 0 - 450.g of a pelleted feed (low NSC, high acid detergent fiber, > 25%) plus 3.2-3.6 kg of grass hay. The same 200 kg donkey at work might be offered 1 to 2 lb (450 g – 900 g) of pelleted feed plus approximately 10 lb (4.5 kg) of grass hay. In summary, at rest the total food offered represents approximately 2% of BW and at work can increase to 2.7 % of BW.

Body Condition
Body condition scoring systems (BCS) for donkeys have been developed throughout the world and are useful to assess if the animals are receiving the proper amount of feed. One BCS described in the NRC 2007 was developed for working donkeys in Africa. This BCS is based on scores given for the donkey’s back and flank on a scale of 1 to 4 (1-emaciated, 2-thin, 3-average, 4-good). Obesity can be a problem with some non-working donkeys in North America and other developed countries and a different BCS should be used to represent this reality. Donkeys tend to accumulate fat on the neck, on either side of the chest wall giving a saddlebag appearance and around the buttocks. A thick roll of fat along the crest of the neck indicates obesity in donkeys. This roll of fat is difficult to reduce with diet after it has formed. Obese donkeys should undergo gradual weight loss, no more than 2 – 4 kg (4.4-8.8 lb) per month equating to approximately 1-2 cm of heart girth. The loss of more than the recommended weight per month can cause metabolic disorders such as hyperlipidaemia. This condition could be also the result of another illness where the appetite is reduced such as colic, flu, laminitis, pneumonia, etc. The mortality rate for hyperlipidaemia in donkeys is high and epidemiological studies indicate that females and obese animals are more sensitive to this medical condition.

Mineral & Vitamin Requirements
Little is known of the specific requirements of minerals and other nutrients for donkeys. Salt requirements of donkeys vary according to their level of physical activity and animals should have free access to a salt block Mineral Blocks should be offered if animals are kept on pastures, particularly if the soils are deficient in certain micro-minerals. Copper and zinc deficiencies (measured in blood plasma) have been reported in working donkeys in Africa and associated with skin lesions. In North America, there have been unconfirmed reports on acute selenium deficiencies in miniature donkeys. With regards to nutrient requirements, we can assume that in the meantime the horse can still be used as a model for the donkey and until specific research on donkeys is performed. However, we should be cautious as donkeys are adapted to live in harsher environments and are able to subsist on a higher forage diet than horses and ponies. As indicated above, it has been reported that the nutrient and energy requirements for donkeys are in the order of 75% of those published for horses. This is a good starting point. Certainly research is needed to understand the nutrient needs of this particular equid.