Nutrition

Elephants are the largest extant herbivores on earth. One of the most prominent features of the elephant is the trunk, which aids them in reaching high branches in search of food. Although these trunks are capable of taking down entire trees, they can also be gentle enough to delicately pick a single blade of grass (Ullrey et al., 1997).  However, not much is known regarding the nutrient needs of elephants, with the exception of energy requirements for basal metabolic functions and for maintenance Ullrey et al., 1997). Nutrition has mainly been theorized from field studies of the horse Ullrey et al., 1997).

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The metabolic rate-body size relationship suggests that the African elephant should be the least selective in terms of their diet. In terms of the study done by Owen-Smith and Jonas (2012), selective feeding amongst mammalian herbivores is expressed as the amount of plant parts consumed, rather than the diversity of the plant species that makes up the diet. In order to learn about the nutritional distribution within elephants, Owen-Smith and Jonas (2012) investigated the variation in selected species ingested by the elephants. The authors hypothesized that the elephants would select for a greater proportion of stem tissue in their diets due to the higher amounts of dietary contribution (Owen-Smith and Jonas, 2012). 

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During the wet season, more than 60% of  the the estimated nutritional contribution came from the woody plants B. massaiensis and B. petersiana while only B. massaiensis made up 40% of the diet during the hot dry season and other species made up about 10% of total ingestion (Owen-Smith and Jonas, 2012). A total of 6 woody species made up more than 90% of the estimated diet during the wet season and 8 species during the hot dry season (Owen-Smith and Jonas, 2012). In terms of plant part contribution, leaves contributed 45% while shoots had an intake of 25% in the wet season (Owen-Smith and Jonas, 2012). The bulk of leaves came from B. massaiensis and B. petersiana while shoots were from B. petersiana along with a range of other species (Owen-Smith and Jonas, 2012). The hot dry season diet mainly consisted of stems (55%) and bark (25%) from the plant B. massaiensis and roots (14%) (Owen-Smith and Jonas, 2012). A majority of the root intake came from C. zeyheri, B. petersiana, Commiphora mossambicensis, and T. sericea (Owen-Smith and Jonas, 2012).

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Based on the data collection, about 40-70% of food consumption came from woody plants with a handful of shrub species (Owen-Smith and Jonas, 2012). Restrictions on the range of woody plants ingested suggests the presence of plant secondary metabolites functioning as toxins or digestion inhibitors (Owen-Smith and Jonas, 2012). Nevertheless, larger herbivores are able to accommodate the diluting effect of secondary chemical contents on nutritional value because of their hindgut fermentators (Owen-Smith and Jonas, 2012). The hindgut fermentators allows large herbivores to process toxic chemicals found in vegetation (Owen-Smith and Jonas, 2012).

 

A study conducted by Ullrey et al. (1997) analyzed plant parts eaten by African elephants in order to determine the usual nutrient intake in wild species (Ullrey et al., 1997). Graze species consumed by the elephants had crude protein concentrations ranging from 8-24% while grass had  a concentration of  3-6% (Ullrey et al., 1997). Woody plants are known to have their highest concentration in crude protein after their first growth which usually goes from September to October while grass species concentrations are highest in late November to December (Ullrey et al., 1997). When the percentage of crude protein is low, the bacteria responsible for digestion cannot sustain adequate levels to process forage. A male elephant was released into Tsavo National Park, Kenya, and the scientists observed a total of 64 plant species eaten. Out of all the plants, crude protein concentrations ranged from 6-23% (Ullrey et al., 1997).

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Crude fiber, another source of nutrition, can either be indigestible or digested but only through symbiotic microorganisms that live in the digestive tract such as the rumen and reticulum (Ullrey et al., 1997). Fiber is known to be a negative component of animal food because of the association of crude fiber with lowered digestibility. On the contrary, the physiochemical characteristics of dietary fiber play an important role in the gastrointestinal function of animals that have evolved as herbivores (Ullrey et al., 1997).The amount of fermentation is directly affected by the amount of digest reaching the lower gut (Ullrey et al., 1997). With low fiber concentrations and high concentrations of fermented materials, fermentation rates increase and gut motility is worsened resulting in abdominal pain (Ullrey et al., 1997). Crude fiber concentrations ranged from 13-62% and were mainly found in grasses, grass bases, stems, and leaves (Ullrey et al., 1997).

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