Nutrition in Ungulates and Subungulates

Artiodactyla (even-toed ungulates) and Perissodactyla (horses, tapirs, and rhinoceros) are ungulates. Perissodactyla have an enlarged cecum to digest materials. Artiodactyla can be divided into browsers, intermediate feeders, and grazers. Most Artiodactyla are ruminants and have a stomach with four compartments.

Elephants and hyraxes are subungulates.

Ungulates and subungulates that are ruminants, or hindgut fermenters, have specialized digestive systems that use bacteria to break down plant carbohydrates. Ungulates and subungulates can be divided into concentrated selectors (browsers), intermediate feeders (browsers/grazers), and grass or roughage eaters (grazers). For more information, see the table Types of Ruminants From Africa, North America, Europe, and Asia.

In nature, browsers prefer highly digestible young leaves from trees and shrubs and can digest substantial amounts of lipids, proteins, and starches. In captivity, they typically consume mostly grass or grass hay. However, grass and grass hay should not be presented to browsers; instead, alfalfa (lucerne) and browse (leaves and branches) should be preferably fed. Browsers have a higher chance of rumen acidosis if they ingest too much highly digestible carbohydrate (mono- and oligosaccharides). Rumen acidosis regularly occurs from feeding inappropriate pellets or too much domestic fruit or bread. Fruit contains mostly highly digestible carbohydrates, which can have a negative effect on the digestive system if fed in huge amounts and can cause acidosis, especially in browsers. Feeding fruits and greens is not recommended, because these foods have limited nutritional value compared with browse (leaves and twigs), grass, hay, or pellets.

Plant carbohydrates can be divided into the following groups:

• Cell content: contains organic acids, mono- and oligosaccharides, starches, and fructans, which are easily digestible carbohydrates

• Cell wall: contains pectic substances (galactans and B-glucans), hemicellulose, and cellulose. Pectic substances are more digestible than hemicellulose and cellulose, which are only digestible by animals with a specialized digestive system. Hemicellulose content can be measured as the difference between the amount of analyzed ADF (acid detergent fiber) and NDF (neutral detergent fiber), and cellulose is the difference between the amount of analyzed ADL (acid detergent lignin) and ADF.

• ADL: ADL is not digestible and is mostly considered a part of the plant carbohydrates.

In general, browsers can digest limited amounts of the cellulose fraction of cell walls. Grazers are less susceptible to rumen acidosis than browsers, although it depends on the species. The chewing system of browsers is adapted to eating leaves by adjustments of their teeth as well by their enlarged saliva system, which can detoxify some but not all toxins (eg, some tannins).

Grazers in general have a highly developed digestive system, through which they can more easily digest high-fiber grasses and roughage.

The digestion of leafy materials and grass is less developed in Perissodactyla than in grazers. This group is also susceptible to acidosis caused by feeding highly digestible carbohydrates.

Knowing which species of leaves, bulbs, flowers, and stems can be fed is imperative. Some plants (or plant parts) contain compounds that can be toxic even in small amounts. Check the literature and consult experts before feeding.

There are no official nutritional requirements available for the group of ungulates and subungulates. However, suggested feeding guidelines (eg, Hay and Pellet Ratios: Considerations in Feeding Ungulates) can be found for different species on the Nutrition Advisory Group (NAG) website and the European Zoo Nutrition Group's resource website, which are set up by nutritional experts and regularly updated based on the most recent literature.

Roughage should be fed to ungulates and subungulates ad lib. The primary roughage for browsers is browse (leaves and twigs); for grazers, it is grass. However, in captivity, the natural diet is not available and is substituted by products that are more or less similar.

Browsing animals should be fed leaves as much as possible. In areas where no fresh leaves are available in winter, good-quality frozen, dried, or silage leaves can be fed. If the amount of leaves to be fed is limited, roughly one-third of the diet should consist of leaves, one-third of a good-quality alfalfa, and one-third of a browser pellet with a maximum of 40% on a dry-matter basis.

If leaves are not available, the diet should consist of two-thirds of good-quality alfalfa and one-third of a browser pellet. However, more digestive diseases can occur on this diet, which can also have a negative effect on the lifespan of the browser.

The diet of grazers should consist of good-quality grass or hay. Analyzing every batch of hay and then adjusting the amount of pellets accordingly is advised. Supplementing with a limited amount of grazer pellets (up to 20% of the whole diet) is necessary to supply vitamins and minerals and a limited amount of digestible fiber because most commercially grown grass and hay are deficient in some vitamins and minerals. Feeding too many pellets can cause GI diseases and obesity.

Intermediate feeders should have a mixture of a browsing and a grazing diet. In practice, this means these animals can be fed with both grazer and browser pellets, and hay and alfalfa/browse, or both diet types can be implemented during different seasons. Some species-specific pellets, such as for (black) rhino, elephant, and tapir diets, are commercially available.

In the common situation in which animals are fed as a group rather than as individuals, pelleted diets are preferred that are not excessively high in energy and that contain sufficient fiber to support proper rumen or colon function. This precaution decreases the possibility of untoward effects caused by overconsumption of concentrates. A pellet sized 5–10 mm is advised, depending on the body size of the species.

Not all hay has the same nutrient content. Legume hays are higher than grass hays in nitrogen and calcium and, if of good quality, are also more digestible. Hay should be leafy and green, free of mold, dirt, excess weeds, and other foreign matter, and should not be overmature (harvested late or stored for > 1 year) or stored wet. Hay analyses can be very useful to evaluate quality.

Whether overmature or subject to bad weather or growing conditions, poor hay may have a good fiber percentage, but protein quality and mineral status, especially of calcium, can be low. Low levels of calcium can cause poor bone calcification and also affect blood calcium levels, which can cause problems during delivery of offspring.

First-cut hay generally contains relatively high amounts of sugar and protein and lower amounts of fiber, depending of the length of the grass when cut and the amount of fertilizer used. Third-cut hay contains relatively low amounts of sugar and protein and higher amounts of fiber. Second-cut hay, in general, has a sugar and protein composition somewhere between first- and third-cut hay. However, the composition can vary, depending on the kind of grass and herb species harvested, soil composition, cutting length, time of year, and amount of fertilizer used.

Most good, harvested hay is palatable; however, a poor-quality or bad-quality hay may also be well consumed. Palatable hay should always be analyzed for dry matter, crude protein, crude fat, NDF, ADF, ADL, calcium (Ca), phosphorus (P), magnesium (Mg), manganese (Mn), and selenium (Se) because hay comprises the major part of ungulate and subungulate diets. Care should be taken to ensure that hay does not contain toxic chemicals, poisonous plants, traces of pests, or fungi and is stored away from excessive heat that can deplete the hay's nutrients. Precautions also should be taken if feeding silage products. If silage was improperly processed or stored or contaminated by animal or meat products, it may contain toxic fungi or Clostridium botulinum bacteria.

Browse consists of leaves, bark, and branches of edible trees and shrubs. Animals that eat browse consume mostly leaves. Browse can be cut during the growing season and then fed directly. In temperate areas, browse should be stored for winter and spring feeding. It can be stored dried, frozen, or as silage. Preservation for winter can be done on-site, although equipment and experienced staff are needed. Browse stored as silage can cause an animal's death if the silage is not preserved properly. Obtaining browse from a commercial provider is preferred.

Appropriate browse species to feed include alder (black and gray), ash, aspen, bamboo, birch, blackberry, elm (field, wych), grapevine, hazel, hornbeam, lime, maple, hawthorn, nettle, plane tree, poplar (black), rose (dog), and willow, but not sycamore, which contains a toxin in its leaves and seeds. Other browse species can also be fed; however, they may contain high amounts of tannins or other unwanted toxins that can harm some animal species. Recent literature on plants should always be checked for updated toxin information before feeding an animal a new plant species. Be aware of chemicals that may have been sprayed on leaves, and check for potential contamination with unwanted bacteria, fungi, insects, or bird feces. Flowers and seeds from browse species should not be fed unless they are known to be safe.

To minimize contamination and wastage, hay should be fed from a rack rather than off the ground for most species (elephants are an exception, because they naturally forage off the ground). Hay racks should be located at eye level for tall browsers such as giraffes and gerenuks. Pellets can be offered from a covered trough or rubber feed pans or by automatic feeding systems, so food can be provided to animals when the keepers are not around. Regularly feeding pellets in an animal’s holding area can facilitate close observation and easy capture. If possible, animals should be fed separately to ensure that each individual receives a similar amount of food. If feeding separately is not possible, at least two widely separated feeding stations may be necessary to decrease conflict and to ensure that subordinate animals obtain their share of food.

In addition to hay and pellets, sometimes assorted fruits and vegetables are fed to exotic ungulates. For most species, these items usually are not necessary except for (occasional) training purposes; fruits and vegetables should be limited to < 5% of the total diet. The exception might be for those species that regularly feed on fruits and succulents in the wild.

Ungulates and subungulates should always have a salt block available, preferably with a balanced vitamin and mineral supplement. Several salt blocks are available, depending on the species. Specific exotic salt blocks are also available that contain higher amounts of specific vitamins and micro- and macroelements. Excessive licking of salt blocks can lead to neurotic behavior and should be prevented.

Most hay or grass fed to ungulates and subungulates contains only limited amounts of Ca, P, biotin, Se, and vitamins A, D and E. Supplementing the diet with extra biotin, vitamin B complex, and unsaturated fatty acids, as well as macroelements like Mg, sodium (Na), and potassium (K) and microminerals like copper (Cu), cobalt (Co), Mn, iodine (I), iron (Fe), and zinc (Zn), is suggested. Oversupplementation should be prevented; for example, high amounts of supplemental Fe may cause hemosiderosis in some browser species.

Amounts of easily digestible carbohydrates and of ADL should be kept low as well. Browser pellets should be fed up to 35% of the total diet and grazer pellets up to 20% of the diet.

Pellets should be palatable and should contain the necessary foodstuffs for the specific group of animals. Many pellets are available for ungulates and subungulates, although no specific pellet type is recommended. Pellets should be made by a company in cooperation with nutrition experts from North American or European exotic animal nutrition groups (eg, Comparative Nutrition Society, NAG, or ENG) or with experts on ungulates and subungulates elsewhere in the world.

Elephants should be fed a grazer pellet with supplemental calcium. Because of their sensitivity to hemosiderosis, black rhinos should be fed a diet with a low level of iron (< 100 mg/kg dry matter). It is speculated that other ungulate species, especially browsing species, may also be subject to hemosiderosis.

All ungulates should be exposed to UVB from sunlight, because supplementation of vitamin D in some cases (elephant, kudu) may be insufficient.

See the table Suggested Analyses of Browser and Grazer Pellets. It is based on several compositions of proven commercial pellets, although in practice, other pellet compositions might also be used and are proven.

• Clauss M, Dierenfeld ES. The nutrition of "browsers". In: Fowler ME, Miller RE, eds. Zoo and Wild Animal Medicine: Current Therapy. Vol. 6. Elsevier; 2008:444-454.

• Clauss M, Kaiser T, Hummel J. The morphophysiological adaptations of browsing and grazing mammals. In: Gordon IJ, Prins HHT, eds. The Ecology of Browsing and Grazing. Springer; 2008:47-88.

1. Hofmann RR. Morphological classification of Sika deer within the comparative system of ruminant feeding types. Deer. 1982;5:352-353.

2. Hofmann RR. Adaptive changes of gastric and intestinal morphology in response to different fibre content in ruminant diets. In: Bell L, Wallace G, eds. Proceedings of Dietary Fibre in Human and Animal Nutrition Symposium. Royal Society of New Zealand; 1983:51-58.

3. Hofmann RR. Evolutionary steps of ecophysiological adaptation and diversification of ruminants: a comparative view of their digestive system. Oecologia. 1989;78(4):443-457. doi:10.1007/BF00378733