Nutrient Composition of Locally Available Browses Consumed by Matschie's Tree Kangaroos (Dendrolagus matchiei) in Six North American Zoological Facilities

Abstract

Locally collected browses (n=17 spp.) consumed by Matschie’s tree kangaroos (Dendrolagus matschiei) in 6 North American zoological institutions were analyzed for comparison with native plants eaten by this species in Papua New Guinea to evaluate dietary suitability. Primary nutrients including crude protein and fat, fiber, starch, non-fiber carbohydrates, and ash were determined using standard analytical methods for forages. Macrominerals calcium (Ca), phosphorus (P), magnesium (Mg), potassium (K), sodium (Na) and sulfur (S), as well as trace elements copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo) and zinc (Zn) were quantified in leaf (n=18), flower (n=1), twig (n=9) and bark (n=6) samples. Tannin content was estimated through the bovine serum albumin methodology. On a dry matter basis (DMB) , foods averaged (± SD) moderate protein (12 ± 5%) and soluble carbohydrate (27 ± 12%) content, along with low starch (1 ± 1%) and crude fat (3 ± 2%) values, and moderate to high values in fiber fractions (neutral detergent fiber 49 ± 15%, acid detergent fiber 33 ± 13%, lignin 11 ± 5%). Macromineral concentrations (Ca 2.2 ± 1.6%, P 0.2 ± 0.1%, Mg 0.3 ± 0.2%, K 1.5 ± 0.6%, Na 0.03 ± 0.04%, S 1.2 ± 1%) and select trace minerals were within anticipated ranges (Cu 11 ± 5 mg/kg, Mo 1 ± 1 mg/kg and Zn 33 ± 18 mg/kg); exceptions Fe (122 ± 11 mg/kg) and Mn (51 ± 81 mg/kg) were considered on the high end of dietary adequacy for most herbivores. Leaves differed significantly from woody parts for all proximate nutrients, as well as K, S, Fe, and tannin content. Consumed in a 50:50 DMB ratio, locally available browses provide similar nutrient profiles as plants eaten by free-living tree kangaroos. Combined data provide information useful in establishing nutrient targets for dietary development, leading to improved health, welfare, and feeding management of tree kangaroo populations under human care.

Full text

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*Corresponding author: E-mail: edierenfeld@aol.com;
Journal of Agriculture and Ecology Research International
21(11): 10-17, 2020; Article no.JAERI.64904
ISSN: 2394-1073
Nutrient Composition of Locally Available Browses
Consumed by Matschie’s Tree Kangaroos
(Dendrolagus matchiei) in Six North American
Zoological Facilities
Ellen S. Dierenfeld
1*
, Marisa Bezjian
2
and Lisa Dabek
3
1
LLC Nutrition Consulting, 4736 Gatesbury Drive, St. Louis, MO 63128, USA.
2
Zoo Miami, 12400 SW 152
nd
Street, Miami, 33177, Florida,
USA.
3
Woodland Park Zoo, 5500 Phinney Avenue N, Seattle, 98103, Washington,
USA.
Authors’ contributions
This work was carried out in collaboration among all authors. Author ESD designed the study, wrote
the sample collection and handling protocol, performed the statistical analyses, and drafted the
manuscript. Authors MB and LD contributed with sample submission, data interpretations, funding and
literature acquisition. All authors read and approved the final manuscript.
Article Information
DOI: 10.9734/JAERI/2020/v21i1130177
Editor(s):
(1) Dr. Daniele De Wrachien, State University of Milan, Italy.
Reviewers:
(1)
N. Deepak Venkataraman, GRT Institute of Pharmaceutical Education and Research, India.
(2)
Boukeloua Ahmed, University Larbi Ben M’hidi Oum el Bouaghi, Algeria.
Complete Peer review History:
http://www.sdiarticle4.com/review-history/64904
Received 25 November 2020
Accepted 30 December 2020
Published 31 December 2020
ABSTRACT
Locally collected browses (n=17 spp.) consumed by Matschie’s tree kangaroos (Dendrolagus
matschiei) in 6 North American zoological institutions were analyzed for comparison with native
plants eaten by this species in Papua New Guinea to evaluate dietary suitability. Primary nutrients
including crude protein and fat, fiber, starch, non-fiber carbohydrates, and ash were determined
using standard analytical methods for forages. Macrominerals calcium (Ca), phosphorus (P),
magnesium (Mg), potassium (K), sodium (Na) and sulfur (S), as well as trace elements copper
(Cu), iron (Fe), manganese (Mn), molybdenum (Mo) and zinc (Zn) were quantified in leaf (n=18),
flower (n=1), twig (n=9) and bark (n=6) samples. Tannin content was estimated through the
bovine serum albumin methodology. On a dry matter basis (DMB) , foods averaged (± SD)
moderate protein (12 ± 5%) and soluble carbohydrate (27 ± 12%) content, along with low starch (1
± 1%) and crude fat (3 ± 2%) values, and moderate to high values in fiber fractions (neutral
Original Research
Article

Dierenfeld et al.; JAERI, 21(11): 10-17, 2020; Article no.JAERI.64904
11
detergent fiber 49 ± 15%, acid detergent fiber 33 ± 13%, lignin 11 ± 5%). Macromineral
concentrations (Ca 2.2 ± 1.6%, P 0.2 ± 0.1%, Mg 0.3 ± 0.2%, K 1.5 ± 0.6%, Na 0.03 ± 0.04%, S 1.2
± 1%) and select trace minerals were within anticipated ranges (Cu 11 ± 5 mg/kg, Mo 1 ± 1 mg/kg
and Zn 33 ± 18 mg/kg); exceptions Fe (122 ± 11 mg/kg) and Mn (51 ± 81 mg/kg) were considered
on the high end of dietary adequacy for most herbivores. Leaves differed significantly from woody
parts for all proximate nutrients, as well as K, S, Fe, and tannin content. Consumed in a 50:50
DMB ratio, locally available browses provide similar nutrient profiles as plants eaten by free-living
tree kangaroos. Combined data provide information useful in establishing nutrient targets for
dietary development, leading to improved health, welfare, and feeding management of tree
kangaroo populations under human care.
Keywords: Browse; herbivore; marsupial; nutrition.
1. INTRODUCTION
A recent publication documented chemical
composition of 24 spp. of foods eaten by the
endangered Matschie’s tree kangaroo
(Dendrolagus matschiei) in Papua New Guinea,
including ferns, shrubs, vines, orchids,
herbaceous plants, and tree leaves [1]. These
native forages were found to contain moderate
levels of protein and soluble carbohydrates,
moderate to high fiber levels, low crude fat and
starch content, and generally expected mineral
concentrations. Conversely, diets fed to the
arboreal tree kangaroos in zoological institutions
reportedly contain few browse plants, but rather
ingredients containing high sugar and starch,
with low fiber concentrations [2]. As a
consequence, zoo-housed individuals can weigh
up to 50% more than healthy, free-living tree
kangaroos [3,4], a condition which may
contribute to suboptimal reproduction observed
in zoo populations through demographic
assessment [5].
This study was undertaken to evaluate nutritional
parameters in locally available browses fed to
tree kangaroos in North American zoos as
suitable substitutes for native foods.
2. MATERIALS AND METHODS
Preferred locally available browse species fed in
six US zoological facilities were collected,
separated into edible fractions (i.e. leaves, twigs
and/or bark) as determined by caretaker feeding
observations, and weighed both prior to and
following air drying to determine fresh water
content. Samples were coarsely ground using a
coffee mill, and shipped to Dairy One Forage
Laboratory (Ithaca, NY, USA) where they were
further ground to 1 mm particle size prior to
analysis for crude protein, crude fat, starch, non-
fiber carbohydrates (NFC) and fiber fractions
including neutral detergent fiber (NDF), acid
detergent fiber (ADF), and lignin using standard
analytical methods for forages. Ash content was
determined via incineration of organic matter,
and macrominerals calcium (Ca), phosphorus
(P), magnesium (Mg), potassium (K), sodium
(Na) and sulfur (S), as well as trace elements
copper (Cu), iron (Fe), manganese (Mn),
molybdenum (Mo) and zinc (Zn) were quantified.
For mineral analyses, samples were digested
using a CEM Microwave Accelerated Reaction
System (MARS6) with MarsXpress Temperature
Control in 50-ml calibrated Xpress Teflon PFA
vessels with Kevlar/fiberglass insulating sleeves
(CEM, Mathews, NC, USA) and then analyzed by
ICP using a Thermo iCAP 6300 Inductively
Coupled Plasma Radial Spectrometer (Thermo
Fisher Scientific Inc., Waltham, MA USA).
Subsamples (5 to10 g dry weight) were
submitted to the W ildlife Nutrition Laboratory at
Washington State University (Pullman, WA,
USA) for tannin analysis utilizing the bovine
serum albumin (BSA) precipitation method
described by Martin and Martin [6].
3. RESULTS AND DISCUSSION
Chemical composition and tannin content from
34 samples representing 17 species of browses
and plant parts consumed by tree kangaroos in
select US zoos are found in Table 1. Mineral
concentrations are displayed in Table 2, and
mean (± SD) values in vegetative (leaves,
flowers) portions are compared with woody
segments (bark, twigs) in Table 3.

Dierenfeld et al.; JAERI, 21(11): 10-17, 2020; Article no.JAERI.64904
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Table 1. Chemical composition of locally harvested browses eaten by Matschie's tree kangaroos (Dendrolagus matschiei) in North American zoological institutions. Data (except
water) on a dry matter basis
Scientific Common Sampling Water Crude
Protein
ADF NDF Lignin NFC Starch Crude
Fat
Ash Tannin
mg BSA
Name Name Part Location/Month <------------------------------------%-----------------------------------> /mg
Acacia longifolia Golden/coast wattle Leaf San Diego CA/Sep 18.7 12.1 26.9 35.1 15.1 39.2 0.4 3.0 10.7 0.0874
Twig 19.7 5.2 52.4 70.6 12.8 18.3 0.2 1.7 4.2 0.0611
Bauhinia X blakeana Hong Kong orchid Leaf Miami FL/Dec 49.0 16.1 31.0 51.4 10.3 14.9 1.2 5.2 12.4 0
Betula spp. Birch Leaf Lincoln NE/Oct 60.9 15.6 21.3 36.9 9.5 32.2 0.4 7.7 7.6 0.0710
Buddleja spp. Butterfly bush Leaf Seattle WA 15.7 16.1 23.7 5.8 48.4 0.6 4.0 8.3 0
Flower 13.1 22.5 31.6 7.7 47.7 0.4 2.6 5.0 0
Bark 6.9 46.6 57.6 22.3 28.0 1.3 2.5 4.9 0
Bursera simaruba Gumbo limbo Leaf Miami FL/Dec 54.9 11.6 19.7 27.3 8.9 49.2 0.7 3.1 8.8 0.1340
Twig 63.0 4.9 33.0 40.9 10.6 42.0 1.7 1.8 10.4 0.0845
Bark 69.6 4.6 43.9 50.5 19.6 31.1 1.7 3.1 10.7 0.0637
Celtis occidentalis Hackberry Leaf San Antonio TX/Nov 12.7 16.1 31.9 3.6 24.8 0.3 6.9 23.9 0
Cotoneaster spp. Cotoneaster Leaf Seattle WA 13.9 28.1 39.7 8.7 35.7 1.0 3.8 7.0 0.0429
Twig 6.0 48.2 63.4 8.1 25.3 1.2 1.8 3.5 0.0527
Bark 5.3 42.1 52.8 12.7 35.5 0.1 2.1 4.3 0.0525
Ehretia anacua Anacua Leaf San Antonio TX/Nov 14.1 18.5 30.1 4.0 28.7 1.7 2.4 24.7 0
Elaegnus pungens Thorny olive Leaf Seattle WA 18.5 45.8 60.3 18.0 13.2 0.3 2.1 5.9 0
Bark 14.1 52.1 63.6 24.1 16.6 0.6 1.0 4.7 0.0299
Fagus grandifolia Beech Leaf Providence RI 50.0 17.0 24.8 46.4 8.9 28.6 1.4 2.9 5.1 0.0649
Twig 37.5 5.9 49.3 68.0 19.2 21.1 0.9 2.1 2.9 0.0247
Ficus benjamina Ficus Leaf Miami FL/Dec 65.1 9.9 37.0 49.5 14.0 6.3 1.2 5.3 29.0 0
Ficus nitida Jewel leaf ficus Leaf San Diego CA/Sep 4.0 7.9 27.5 38.9 11.3 36.6 1.1 2.3 14.3 0.0719
Twig 18.0 6.8 45.2 59.1 14.8 25.4 0.8 1.7 7.0 0.0495
Grewia occidentalis Crossberry Leaf San Diego CA/Sep 28.0 19.3 19.1 45.3 4.9 18.8 0.7 5.0 11.5 0.0427
Twig 37.0 9.5 47.4 76.3 9.0 5.9 <0.1 0.9 7.3 0
Morus spp. Mulberry Leaf Lincoln NE/Oct 66.4 22.3 14.2 23.1 3.3 30.8 0.6 4.1 19.8 0
Twig 47.3 7.6 50.5 65.7 14.7 17.2 1.3 2.2 7.3 0
Bark 49.0 7.7 41.5 50.3 10.3 28.1 5.5 4.4 9.5 0
Morus spp. Mulberry Leaf Providence RI 65.4 24.3 14.2 28.1 3.1 34.0 0.9 3.2 10.4 0
Twig 52.4 8.3 53.0 70.3 12.4 15.2 1.4 1.7 4.6 0
Phyllostachys spp. Bamboo Leaf Providence RI 51.5 18.3 26.3 63.2 3.6 9.7 0.4 3.1 5.7 0
Ulmus parvifolia Chinese elm Leaf Lincoln NE/Oct 52.9 18.7 19.7 42.1 5.6 13.7 0.7 4.6 20.9 0.0167
Twig 45.6 10.1 40.4 55.0 14.1 24.1 2.4 2.2 8.6 0
Bark 48.6 9.1 38.7 65.4 13.4 14.1 5.6 2.3 9.2 0.0215
Xylosma spp. Xylosma Leaf San Antonio TX/Nov 11.0 24.1 33.9 9.1 43.3 0.8 2.4 9.3 0
Abbreviations: ADF = acid detergent fiber; NDF = neutral detergent fiber; NFC = non-fiber carbohydrates

Dierenfeld et al.; JAERI, 21(11): 10-17, 2020; Article no.JAERI.64904
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Table 2. Mineral composition of locally harvested browses eaten by Matschie's tree kangaroos (Dendrolagus matschiei) in North American zoological institutions. Data presented on
a dry matter basis
Scientific Common Part Sampling Ca P Mg K Na S Cu Fe Mn Mo Zn
Name Name Location/Month <-------------------%--------------------> <-----------mg/kg---------->
Acacia longifolia Golden/coast wattle Leaf San Diego CA/Sep 2.97 0.27 0.33 1.09 0.11 0.37 13 52 43 0.9 27
Twig 0.87 0.19 0.16 0.97 0.085 0.1 8 66 11 3 20
Bauhinia X blakeana Hong Kong orchid Leaf Miami FL/Dec 4.33 0.16 0.35 0.75 0.003 0.24 7 56 21 0.2 30
Betula spp. Birch Leaf Lincoln NE/Oct 1.76 0.22 0.29 1.73 0.004 0.2 4 118 48 0.3 45
Buddleja spp. Butterfly bush Leaf Seattle WA 0.55 0.4 0.13 2.1 0.009 0.09 21 60 20 0.5 48
Flower 0.73 0.14 0.09 1.57 0.01 0.18 12 83 25 1.7 17
Bark 0.75 0.45 0.19 1.57 0.008 0.22 28 188 26 1.3 40
Bursera simaruba Gumbo limbo Leaf Miami FL/Dec 1.56 0.2 0.31 1.23 0.118 0.67 7 37 11 3.7 24
Twig 2.84 0.24 0.4 1.28 0.143 0.17 9 12 10 1.3 38
Bark 2.33 0.27 0.23 2.52 0.031 0.19 12 29 10 0.7 28
Celtis occidentalis Hackberry Leaf San Antonio TX/Nov 6.26 0.14 0.48 1.56 <0.001 0.21 9 110 29 0.7 17
Cotoneaster spp. Cotoneaster Leaf Seattle WA 1.85 0.2 0.23 1.32 <0.001 0.17 10 82 41 0.6 39
Twig 0.64 0.17 0.11 1.17 0.007 0.1 9 38 13 0.7 24
Bark 1.05 0.16 0.18 1.08 0.006 0.06 8 35 19 0.7 30
Ehretia anacua Anacua Leaf San Antonio TX/Nov 6.98 0.12 1.08 1.48 0.003 0.4 10 119 28 1.5 26
Elaegnus pungens Thorny olive Leaf Seattle WA 1.22 0.18 0.12 1.58 0.005 0.23 9 78 95 0.9 31
Bark 2.44 0.34 0.21 1.23 0.005 0.33 18 139 88 3.6 47
Fagus grandifolia Beech Leaf Providence RI 0.69 0.17 0.14 0.83 0.02 0.17 12 202 449 0.2 49
Twig 0.92 0.14 0.08 0.28 0.017 0.06 12 96 217 0.4 101
Ficus benjamina Ficus Leaf Miami FL/Dec 5.17 0.11 0.39 2.2 0.024 0.17 6 42 9 <0.1 33
Ficus nitida Jewel leaf ficus Leaf San Diego CA/Dec 3.53 0.13 0.35 2.21 0.036 0.17 8 277 27 1 13
Twig 1.85 0.25 0.31 1.52 0.055 0.09 14 60 15 3.3 16
Grewia occidentalis Crossberry Leaf San Diego CA/Sep 2.37 0.29 0.42 2.52 0.028 0.34 14 570 97 2.3 56
Twig 1.1 0.35 0.25 2.33 0.066 0.16 9 47 30 1.6 22
Morus spp. Mulberry Leaf Lincoln NE/Oct 3.75 0.4 0.37 2.2 0.003 0.29 10 227 59 2.4 35
Twig 1.68 0.31 0.17 1.25 0.002 0.1 9 110 24 1.2 32
Bark 2.49 0.22 0.16 0.8 0.002 0.1 13 162 18 0.7 8
Morus spp. Mulberry Leaf Providence RI 1.8 0.38 0.23 2.78 0.004 0.26 8 127 86 1.1 56
Twig 0.8 0.34 0.1 1.5 <0.001 0.1 9 61 38 0.4 42
Phyllostachys spp. Bamboo Leaf Providence RI 0.38 0.19 0.25 1.75 0.004 0.21 13 381 39 1 24
Ulmus parvifolia Chinese elm Leaf Lincoln NE/Oct 3.08 0.28 0.22 1.67 0.002 0.21 8 179 28 0.4 13
Twig 2.24 0.23 0.22 1.37 0.005 0.13 8 130 29 0.3 45
Bark 2.45 0.16 0.2 1.01 0.01 0.11 8 93 7 0.2 20
Xylosma spp. Xylosma Leaf San Antonio TX/Nov 2.68 0.15 0.27 1.49 0.017 0.21 10 66 33 0.5 18
Abbreviations: Ca = calcium, P = phosphorus, Mg = magnesium, Na = sodium, S= sulfur, Cu = copper, Fe = iron, Mn = manganese, Mo = molybedenum, Zn = zinc

Dierenfeld et al.; JAERI, 21(11): 10-17, 2020; Article no.JAERI.64904
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Table 3. Comparison of chemical composition in vegetative (leaves, flowers) compared with woody (twigs, bark) portions of locally sourced browses eaten by tree kangaroos
(Dendrolagus matschiei) in six US zoos. Data (except water) dry matter basis
Water Crude
Protein
ADF NDF Lignin NFC Starch Crude
Fat
Ash Tannins
% % % % % % % % % mg BSA/mg
Mean values in vegetative portions of local browses 47.2 15.4 23.8 38.9 8.2 29.3 0.8 3.9 12.6 0.03
SD; n=19 samples 19.9 4.2 8.0 11.5 4.3 13.5 0.4 1.6 7.4 0.04
Mean values in woody fractions of browses consumed 44.3 7.5 45.6 60.6 14.5 23.2 1.8 2.1 6.6 0.03
SD; n= 15 samples 15.8 2.5 5.7 9.5 4.8 9.2 1.7 0.8 2.6 0.02
P significance of paired samples; n=11; tannins
(n=9 leaf - twig pairs)
<.001 <.001 <.001 ** * * *** ** **
Mean values in native browses from Papua New Guinea 75.6 10.9 39.3 51.8 15.1 26.5 0.9 3.2 7.6 n/a
SD; n=26 samples from 24 spp.
1
10.1 4 10 12.9 6.1 8.4 0.9 1.9 4
Ca P K Mg Na S Cu Fe Mn Mo Zn
<-----------------------%----------------------> <-----------------mg/kg-------------------->
Mean minerals in vegetative portions of local browses 2.7 0.2 1.7 0.3 0.02 0.3 10.1 150.8 62.5 1.1 31.6
SD; n=19 samples 1.9 0.1 0.5 0.2 0.04 0.1 3.7 135.8 97.1 0.9 13.9
Mean minerals in woody fractions of browses consumed 1.6 0.3 1.3 0.2 0.02 0.1 11.6 84.4 37.0 1.3 34.2
SD; n=15 samples 0.8 0.1 0.6 0.1 0.04 0.1 5.4 52.4 53.6 1.1 21.7
P significance of paired samples; n=11 * ** *
Mean values in native browses from Papua New Guinea 1.1 0.2 1.8 0.3 0.02 n/a 11.9 47.5 268.3 n/a 33.9
SD; n=26 samples from 24 spp.
1
1.0 0.1 0.9 0.2 0.0 n/a 12.7 26.0 225.2 n/a 17.7
Abbreviations: ADF = acid detergent fiber; NDF = neutral detergent fiber; NFC = non-fiber carbohydrates; Ca = calcium, P = phosphorus, K = potassium, Mg = magnesium, S= sulfur, Cu = copper, Fe = iron, Mn = manganese, Mo = molybdenum, Zn = zinc; n/a
= not analyzed. (* P=.05; ** P=.01; *** P=.001);
1
Dierenfeld et al. 2020

Dierenfeld et al.; JAERI, 21(11): 10-17, 2020; Article no.JAERI.64904
15
Leaves (n=18) and the single flower sample
analyzed contained moderate protein levels,
varying 3-fold (8 to 24% of dry matter (DM)),
whereas woody fractions (twigs and bark)
contained about half those levels (~5 to 14% of
DM); differences were highly significant (P <
.001) in the 11 samples with paired vegetative:
woody fractions. Similarly, crude fat ranged
almost 4-fold from low to moderate (2 to 8% of
DM in leaves, and 1 to 4% in woody parts (P =
.001; n=11). All starch values in leaves,
regardless of origin, were exceptionally low at
<1.5% of DM; starch content in two bark
samples analyzed at ~5.5% starch, but in
general values were also <1.7% of DM,
nonetheless differed significantly (P = .05; n=10)
between paired portions of the same
samples/species. Plant cell wall constituents
(hemicellulose, cellulose and lignin)
concentrations within the NDF of leaves were
moderate (20 to 60% of DM) and, not
unexpectedly, higher in woody fractions (41 to
76%; P <. 001 for NDF and ADF, P =.004 for
lignin; n=11 paired samples); nonetheless,
lignification index (lignin as a proportion of NDF)
was the same between plant parts, averaging
~22% of NDF fiber. NFC (P = .03) and ash (P =
.005) values also differed significantly between
leaf and woody fractions.
Tannin results revealed that fully 65% of the
North American browse samples contained no or
very low tannin concentrations (<0.03 mg
BSA/mg forage); 30% of native browse samples
contained notable (>0.05 mg BSA/mg forage; 7
samples, 21%) or high levels (>0.075 mg
BSA/mg forage; 3 samples, 9% of samples
submitted). Although no statistical differences
were seen in tannin concentrations measured in
paired samples comparing leaves with bark from
the same species (P = .38; n=6), nor between
paired bark or twig samples from the same
species (P=.12; n=3), twigs contained
significantly less tannin (P = .008) than paired
leaf samples (n=9) from US browses.
Regarding minerals, only K (P = .05), S (P = .01)
and Fe (P = .05) concentrations differed
significantly between the vegetative and woody
fractions analyzed as paired samples (n=11),
with leafy portions always displaying higher
values.
According to reports from caretakers submitting
browse samples, animals always consume
leaves, but only sometimes eat bark or twigs
from the various browses offered. Composition of
native plants/portions eaten by tree kangaroos in
Papua New Guinea [1] appears intermediate to
values measured in leafy compared to woody
fractions of this array of shrubs and trees fed in
North American zoological institutions, with a
ratio of ~50:50 leaves to twig/bark fractions
closely matching the proximate and fiber content
of forages consumed in field habitats. Obtaining
a more accurate estimate of actual intakes and
digestibility of the various plant portions would
allow us to better calculate nutrient contributions
of browses in managed feeding programs for tree
kangaroos.
The low starch, high fiber nutritional profiles
represented by these locally available browses
may indeed provide suitable moderately
digestible forage substrates for the foregut-
fermenting tree kangaroo [2], and contribute to
optimal body condition and digestive physiology.
A low fiber lignification index, as found in these
browses, suggests substantial fermentation
potential, given a proper microbial environment
and adequate residence time in the digestive
tract [7]. The further high fiber, low fat and starch
content of browses would also tend to support,
rather than inhibit, growth of beneficial cellulolytic
gut microbes as is seen in other foregut-
fermenting herbivores [8,9]. Nonetheless,
detailed aspects of digestion, fermentation,
passage, and microbiology in response to
different diets remain to be further examined in
marsupial herbivores.
It may also prove useful to investigate aspects of
dietary tannins in native browses for comparison
with local alternatives; large salivary glands have
been reported in tree kangaroos, a morphological
feature often associated with adaptation to
tannin-containing diets [10]. Although higher
tannin levels are anticipated to possibly impact
palatability, mineral or protein bioavailability, as
well as digestibility [11], no effect has been
reported with inclusion of quebracho tannins in
diets of a browsing macropodid marsupial
(foregut fermenter) or two species of hindgut-
fermenting arboreal folivorous marsupials [12],
suggesting inherent adaptations. Nonetheless,
potential health and/or intake behavioral
implications of these observations remain to be
determined for tree kangaroos, and they clearly
do not seem to avoid concentrations measured in
this study.
Although minerals quantified in browses are
considered to be within expected ranges to meet
known maintenance mineral requirements of

Dierenfeld et al.; JAERI, 21(11): 10-17, 2020; Article no.JAERI.64904
16
domestic herbivores, elevated calcium and iron
concentrations were found in locally sourced
browses, and particularly high and variable (30 to
40-fold) levels of manganese were recorded in
both native and locally sourced browses. Neither
mineral nutrition nor status has been investigated
widely in tree kangaroos, nor have specific
mineral imbalances been reported as health
issues [2,4]. Interactions between Ca and Fe, as
well as impacts of dietary fiber on mineral
bioavailability, may be of future interest for the
species, particularly if higher fiber diets are
implemented in captive populations. Although
trace mineral status (in particular, Cu and Fe),
has been anecdotally suggested as linked with
coat quality and coloration in zoo individuals, no
supportive evidence is found in published
literature. High dietary P and interactions with
Ca can interfere with Fe uptake, and Mn directly
impacts uptake of both Cu and Fe through
competition for absorption binding sites [13], but
the significance of elevated dietary Mn levels for
tree kangaroo health, if any, is unknown at this
time.
Correlations of specific nutrients or anti-nutrients
with palatability rankings of various browses can
be further examined to optimize welfare and
enrichment opportunities for tree kangaroos, as
can regional and seasonal differences in
composition and preferences. The current study
provides initial comparison with native browses
eaten by tree kangaroos, and confirms that
locally sourced plants can provide suitable
nutrient profiles.
4. CONCLUSION
Information obtained to date on browse
composition provides useful guidelines for
lowering calorie content of managed tree
kangaroo diets, particularly through reducing
starch and fat, and increasing fiber content of
diets. Future research monitoring seasonal
selection of browses – possibly including
threshold levels of tannins that may impact intake
behaviors – and time budget allocation for
foraging on these items, may help to define
detailed annual differences in diet composition
and nutritional status of this species. Projects
studying fecal microbiome of free ranging and
captive populations may also be useful for future
diet and health assessment. Overall, the results
contribute to science-based diet
recommendations for improved feeding of tree
kangaroos.
Increased feeding of locally-available browses,
including both leafy and woody fractions, will best
duplicate nutrient profiles of native forages, and
may improve health and reproduction, as well
as lower obesity rates reported for this species in
captivity. Targeted agroforestry practices and
harvesting of suitable browses for use in
herbivore diets should be encouraged to
increase quality ingredient supplies going
forward.
ACKNOWLEDGEMENTS
We appreciate the browse sample identification,
collection and handling from animal care staff at
Lincoln Children’s Zoo, Roger Williams Park Zoo,
San Antonio Zoo, San Diego Zoo, Woodland
Park Zoo, and Zoo Miami. Funding for the study
was supplied through research grants from the
Wild Animal Health Fund (American Association
of Zoo Veterinarians) and the American Zoo and
Aquarium Association’s Tree Kangaroo Species
Survival Program.
COMPETING INTERESTS
Authors have declared that no competing
interests exist.
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