Ruminants

Ruminants are herbivorous animals that store their food in the first chamber of the stomach, called the rumen, when it is first swallowed, then after some digestion has taken place, regurgitate it as “cud,” which is chewed again and reswallowed into another chamber of the stomach for further digestion. This maximizes the amount of nutrition the animal can derive from hard-to-digest plant food. Wild ruminants tend to eat very quickly, getting as much food mass into their rumens as possible, then retiring to places of safety where they can digest at their leisure. There are over two hundred species of ruminants, including sheep, cows, camels, pronghorns, deer, goats, and antelope. They eat lichens, grass, leaves, and twigs.

Ruminants belong to the suborder Ruminantia in the order Artiodactyla. Families include Tragulidae, which is the only group in the infraorder Tragulina. These animals include ten mouse-deer species in three orders. The other families, Giraffidae, Antilocapridae, Cervidae, Moschidae, and Bovidae, belong to the infraorder Pecora. Tylopods have three-chambered stomachs. Examples are camels and llamas. Pecora are sheep, goats, antelope, deer, and cattle. Most pecorids have horns or antlers. These true ruminants have four-chambered stomachs, whose compartments are called the rumen, reticulum, psalterium, and abomasum. The abomasum is most similar to the stomachs of nonruminant mammals, while the other three compartments are developments peculiar to ruminants.

Ruminants chew or grind food between their lower molars and a hard pad in the gums of the upper jaw. The rumen collects partly chewed food when it is first swallowed. The food undergoes digestion in the rumen and passes into the reticulum. There, it is softened by further digestion into cud. Then, the reticulum returns the cud to the mouth for rechewing, which is mixed with more saliva. Swallowing the chewed cud next sends food to the third compartment, the psalterium, for more digestion. The psalterium empties into the abomasum, where food mixes with gastric juices, and digestion continues. Finally, the food enters the intestine, which absorbs nutrients that are then carried through the body by means of blood.

The stomachs of ruminants also contain numerous microorganisms. These help break down the cellulose in plants and protect the ruminant from the effects of any toxins used as defense mechanisms by the plants.

Domesticated Ruminants

Cattle, sheep, goats, and reindeer are all domesticated ruminants, although there are still wild species of each. The world population of these ruminants is slightly less than four billion. Ruminants are useful food sources for humans because they are large mammals, providing a lot of meat, as well as milk, wool, hide, and fuel. Because they eat plants, they are low on the food chain. Since 90 percent of the energy from any food source is lost in digestion, domesticated ruminants are relatively efficient transmitters of food energy from plants to humans. The large size of these ruminants, however, means that their metabolisms are relatively slow, and thus, they can afford the time it takes to digest grasses, leaves, and twigs through rumination, whereas smaller herbivores with higher metabolisms, such as rodents, must digest food more quickly and thus eat more nutrient-rich plant food, such as seeds.

Some Wild Ruminant Species

Wild ruminants are important to food chains because they eat plants, preventing overgrowth. They also are eaten by carnivores and omnivores. Bactrian camels, with three-chambered tylopod stomachs, inhabit the steppes and mountains of the Gobi Desert. These two-humped camels are domesticated as food and draft animals in Afghanistan, Iran, and China. Bactrian camels subsist on a diet of grass, leaves, herbs, twigs, and other plant parts. Their humps contain stored fat. Given the extreme aridity of their native environment, ruminant digestion allows them to derive the maximum nutrition from scarce food supplies.

Chamois goats live in the mountains of Europe and southwestern Asia. Their diet consists of grass and lichens in the summer, while in winter, they eat pine needles and bark. Pronghorns live in the open plains and semideserts of the North American West. They are the only living Antilocapridae, relatives of antelope. These true ruminants eat herbs, sagebrush, and grasses in the summer and dig under the snow for grass and twigs in the winter. The large reindeer of northern Europe and Asia inhabit forests, grasslands, and mountains. Reindeer eat grass, moss, leaves, twigs, and lichens. Sable antelope live in southeastern African woodlands and grasslands, where they eat grass, shrub leaves, and twigs.

Principal Terms

• Artiodactyl: a herbivore that walks on two toes, which have evolved into hoofs
• Carnivore: an animal that eats only animal flesh
• Esophagus: the tube through which food passes from mouth to stomach
• Gestation: the term of pregnancy
• Herbivore: an animal that eats only plants
• Nutrient: a nourishing food ingredient
• Omnivore: an animal that eats both plants and animals

Bibliography

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Constantinescu, Gheorghe M., Brian M. Frappier, and Germain Nappert. Guide to Regional Ruminant Anatomy Based on the Dissection of the Goat. University of Iowa Press, 2001.

Cronje, P. B., E. A. Boomker, and P. H. Henning, eds. Ruminant Physiology: Digestion, Metabolism, Growth, and Reproduction. Oxford University Press, 2000.

Fails, Anna Dee, et al. Anatomy and Physiology of Farm Animals. 8th ed. John Wiley & Sons, Inc., 2018.

Hackmann, T., and J. Spain. “Invited Review: Ruminant Ecology and Evolution: Perspectives Useful to Ruminant livestock Research and Production. Journal of Dairy Science, vol. 93, no. 4, 2010, pp. 1320-34. doi:10.3168/jds.2009-2071

“133 Examples of Ruminants (A to Z List with Pictures).” Fauna Facts, 21 Nov. 2021, faunafacts.com/animals/examples-of-ruminants. Accessed 1 Oct. 2024.

"Ruminants." Merck Animal Health, www.merck-animal-health.com/products/ruminants. Accessed 1 Oct. 2024.

Wilson, R. T. Ecophysiology of the Camelidae and Desert Ruminants. Springer Verlag, 1990.