Chapter 79 Advances in Giraffe Nutrition
In the last decade, numerous publications have been written with regard to the nutrition of giraffe and other ruminant browsers maintained in zoological institutions, inspired by several health problems suspected to have a nutritional origin. Thus, reports of rumen acidosis, chronic wasting, peracute mortality syndrome, energy malnutrition, hoof disease, inverse serum calcium and phosphorus levels, mortality caused by cold stress, overall poor body condition, urolithiasis, serous fat atrophy, chronic energy deficiency, dental disease, and pancreatic disease, among others, have been linked to nutritional imbalances in the giraffe diet.4,7,11,26,29 Traditional giraffe zoo diets in North America consist mainly of low-fiber pellets (ADF-16) and alfalfa hay, with the original pellets designed based on the domestic ruminant.20 Some zoos will occasionally add browse and some produce. This diet is high in soluble carbohydrates (sugars and starch) and low in total fiber. During the 1970s, and to cope with the peracute mortality syndrome reported in the giraffe, it was recommended to feed giraffes a diet containing low fiber and high protein (15% to 18% for adult nonlactating animals and 18% to 20% for calves and lactating cows). The idea of feeding zoo browsers, including giraffe, a low-fiber, high-protein pellet might be partly justified based on earlier studies that reported high levels of nitrogen in the rumen of free-ranging browsers when compared with grazers.
The claim that giraffes should have protein levels of 18% dry matter (DM) in their diet is not supported by any direct studies.7 Traditional zoo commercial browser pelleted feeds such as ADF-16 are composed mainly of alfalfa meal, yellow corn grain, wheat middlings, and molasses. These pellets have the potential to supply high levels of readily fermentable carbohydrates (starch), increasing the availability of free glucose and stimulating the growth of certain ruminal bacteria, thereby increasing the production of volatile fatty acids and decreasing ruminal pH and cellulitic bacteria. Studies with domestic sheep fed ADF-16 pellets, similar to the pellets used in giraffe diets, have shown sheep with a ruminal pH below 6 being maintained for more than 6 hours.19 Starch is negligible in the natural diets of wild browsers. Research has shown that giraffe fed a diet of low- and high-fiber pellets, plus alfalfa hay, will selectively ingest the pellets and alfalfa hay with higher levels of neutral detergent fiber (NDF) and acid detergent fiber (ADF) and lower levels of gross energy, contrary to the idea that giraffe as browsers (concentrate selectors), will select a low-fiber easily digestible diet.1 In 1973, for the first time, it was suggested that browsers such as the giraffe should be fed a diet higher in fiber and lower in protein.11 It took over 30 years for the zoo community to develop similar recommendations.26
A thorough review of the giraffe natural diet has been given by Kearney.14 The giraffe is classified as a concentrate selector (browser) that in the wild consumes mainly foliage, including leaves and twigs of trees and shrubs, herbs and forb, but these will vary with season and geographic location. The diet also includes wild fruits, flowers, bark, thorns, and seed pods.13 Giraffe in their natural environment will strip leaves from terminal shoots with their tongues or bite off the new nonlignified shoot ends, but in the dry season they may consume a significant proportion of lignified material. In the Serengeti, giraffe consume 50% to 80% of the available shoots of favored Acacia species, exerting a major impact on Acacia regeneration. Reports have indicated that giraffe will spend 53% of the daylight hours searching for and consuming food, mainly woody plants. Acacia spp. seem to be consumed the most, but as many as 66 different plant species may be consumed by giraffe in a year.16 Giraffe in their natural environment will consume little or no grass. Certainly, all the stimuli found in their natural habitat in the selection of browse and food are changed in zoo giraffe diets.
The giraffe, being classified as a concentrate selector (browser),3,13 will have different dietary and possibly nutritional requirements than wild grazers. The giraffe, like kudu, moose, gerenuk, and okapi, are considered tree and bush foliage selectors. Browsers, considered early evolved ruminants, had to deal with an inefficient fiber digestion in the rumen because of short retention times. Browsers, in general, focus on cell contents, whereas grazers focus on cell wall constituents.1 As noted, giraffes in zoos have been offered diets high in soluble carbohydrates, low in fiber, and relatively high in protein. These diets originated from the time when wild herbivores were classified as grazers (grass and roughage eaters), concentrate selectors (browsers), and intermediate feeders. The latter might wrongly imply that browsers such as the giraffe are adapted to a diet high in soluble carbohydrates, with potential problems of producing rumen acidosis, as widely reported in domestic ruminants.4 Although the giraffe had been classified as a concentrate selector (browser), there have been studies suggesting that giraffes are not truly concentrate selectors. Giraffes have more omasal laminae, whereas most browsers have few and thick omasal laminae, with the omasum serving as a filter between the reticulum and abomasum for coarse particulate matter, plus having an absorptive surface function. Giraffes, like grazers, have rumens well connected to the abdominal wall and an advanced compartmentalization of the rumen, in contrast with other browsers.16 Furthermore, large ruminants require less energy per unit of volume of gastrointestinal tract, needing less energy-dense feeds than smaller ruminant-browsers. Thus, the giraffe as a large ruminant might not fit the classification of a true concentrate selector, but rather an intermediate feeder or a facultative concentrate selector.
There are not many studies comparing zoo and free-ranging giraffe but, in one study, serum parameters were compared between zoo and free-ranging giraffes.28 The results showed multiple differences in serum nutritional parameters between the two groups of giraffe. A total of 32 free-ranging giraffes and 20 zoo giraffes were used for the comparisons. Serum amino acid levels were higher in free-ranging animals, possible reflecting enhanced activity of the animals. Striking differences were found in the serum concentration of fatty acids. Free-ranging giraffes had higher concentrations of total omega-3 fatty acids because of elevations in α-linolenic, eicosatrienoic, eicosapentaenoic, and docosapentaenoic acids. Zoo animals, on the other hand, showed high levels of total omega-6 fatty acids, particularly linoleic and arachidonic acids due to their high levels in grains. The omega-3–to–omega-6 ratios were 0.48 ± 0.05 and 0.27 ± 0.07 for free-ranging and zoo giraffes, respectively, alerting the authors to recommend supplementation of omega-3 in the diet of zoo giraffes. In a more recent study, the addition of flax seed as a source of linolenic acid increased the serum omega-6 and omega-3 fatty acid levels, improving the omega-3–to–omega-6 ratios.15 Serum cholesterol and saturated fatty acid levels have been seen to be higher in zoo giraffes, probably reflecting the composition of the dietary fatty acids. Serum retinol concentrations were significantly higher in zoo giraffes (89.3 µg/dL) when compared with free-ranging animals (24.1 µg/dL), although results reported in other studies showed less of a difference for retinol among these groups.25 Serum α-tocopherol values in zoo giraffes were low (4.43 µg/dL) when compared with free-ranging animals (41.89 µg/dL),28 although much higher levels of α-tocopherol (109 µg/dL)23 have been reported in zoo giraffes.
Inverse serum calcium-phosphorus ratios were found in 62% of giraffes in a study that measured mineral values in 24 animals at two institutions from samples collected over 9 years.23 Based on ISIS (International Species Information System) reports, captive adult giraffes in general show inverse calcium-phosphorus ratios. Mean serum calcium and phosphorus concentrations were 8.0 ± 0.8 mg/dL (n = 142) and 10.5 ± 2.9 mg/dL (n = 135), respectively.31 In a more recent publication,29 giraffes (n = 10) from five zoological institutions had higher serum calcium levels (8.6 to 10.6 mg/dL), lower serum phosphorus levels (3.1 to 6.2 mg/dL), and normal serum calcium-phosphorus (Ca : P) ratios, ranging from 1.4 to 2.9. The serum phosphorus concentrations were much lower than those reported by ISIS.31 Two recent dietary studies of giraffes have shown positive effects on changing the serum calcium-phosphorus ratio after switching animals from a high-starch, low-fiber pellet (ADF-16) to a low-starch, high-fiber commercial pellet.15,18 In both studies, the serum calcium level was not affected by diet, but the serum phosphorus level was reduced by diet. Calcium homeostasis in vertebrates is precisely regulated, unlike phosphorus and magnesium. The serum phosphorus level was significantly reduced in one of the studies15 when changing from a high-starch, low-fiber to a low-starch, high-fiber diet that also reduced the level of phosphorus in the diet.