Directory UMM :Data Elmu:jurnal:A:Animal Feed Science and Technology:Vol87.Issue3-4.Oct2000:
Animal Feed Science and Technology
87 (2000) 287±296
Short communication
Comparison of the digestive ability of crop ¯uid
from the folivorous Hoatzin (Opisthocomus hoazin)
and cow rumen ¯uid with seven tropical forages
R.J. Jonesa,*, M.A. Garcia Amadob, M.G. Dominguez-Bellob
a
CSIRO Davies Laboratory, PMB, Post Of®ce, Aitkenvale, Townsville, Qld. 4814, Australia
Centro de BiofõÂsica y BiochõÂmica, Instituto de Investigaciones Cientõ®cas (IVIC), Caracas, Venezuela
b
Received 5 October 1999; received in revised form 14 June 2000; accepted 10 August 2000
Abstract
We explored the hypothesis that the Hoatzin, a tropical bird which feeds on tree leaves and has a
crop resembling a rumen, may have a better ability to digest tanniniferous feeds than do cattle.
Comparisons were made between Hoatzin crop ¯uid (HCF) and cow rumen ¯uid (CRF) in in-vitro
digestion studies using freeze dried leaves of six tropical tanniniferous shrub legumes and the
tropical grass Panicum maximum. In-vitro dry matter digestibility (IVDMD) and in-vitro nitrogen
digestibility (IVND) were measured in the presence and absence of polyethylene glycol (PEG) to
minimise the effect of condensed tannin.
For all plant species, and in the presence or absence of PEG, the CRF gave higher IVDMD and
IVND than did HCF (P < 0:01). The interaction of PEG animal (P < 0:01) for IVDMD was due
to an absence of response with CRF (62.1 v 63.0%) and a large response with HCF (43.5 v 37.4%).
Similarly for IVND, the response to PEG with CRF was much smaller (83.4 v 75.6%) than for HCF
(51.9 v 26.5%) (P < 0:01).
PEG had no signi®cant effect on IVDMD or IVND of the CT-free Panicum maximum by HCF or
CRF (P > 0:05). However, values were much higher with CRF: 74.2 v 30.6% and 81.3 v 29.0%,
respectively.
The only legume to have reasonable levels (>55%) of IVDMD and IVND with HCF in the
absence of PEG was Gliricidia sepium, which has little or no free condensed tannins. Acacia
boliviana, Calliandra calothyrsus and Leucaena trichandra gave low values and those for L.
leucocephala and L. pallida were intermediate.
The low IVDMD and IVND with HCF, together with the large response to PEG, clearly show
that high tannin content in the diet cannot be handled by the Hoatzin. Low tannin content in the
crop contents indicates that it avoids highly tanniniferous leaves. This supports other ®ndings that
the Hoatzin is extremely selective of a high quality leafy diet.
*
Corresponding author. Tel.: 61-747538500; fax: 61-747538600.
E-mail address: raymond.jones@tag.csiro.au (R.J. Jones).
0377-8401/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 3 7 7 - 8 4 0 1 ( 0 0 ) 0 0 1 9 9 - 1
288
R.J. Jones et al. / Animal Feed Science and Technology 87 (2000) 287±296
It is concluded that the Hoatzin is an unlikely source of bacteria to improve the feeding value of
tropical tanniniferous shrub legumes for cattle. # 2000 Elsevier Science B.V. All rights reserved.
Keywords: Tanniniferous shrubs; Condensed tannins; In-vitro digestibility; Foregut fermentation; Hoatzin
1. Introduction
The Hoatzin (Opisthocomus hoazin) is a folivorous bird native to areas of South
America. It is unique in having a digestion pattern similar to that in ruminants (Grajal
et al., 1989). It feeds on the leaves of many riverine tree species. These trees belong to
plant families known to have a variety of toxic principles. Among these toxic compounds
are phenols and tannins (Dominguez-Bello et al., 1994). It has been hypothesised that
these birds may have the ability to detoxify these antinutritive compounds by its foregut
fermentation.
In this paper, we examine this hypothesis by comparing the digestion in-vitro of several
tropical tanniniferous browse species which are being evaluated for cattle production in
Australia. The aim of the work was to assess the potential of the Hoatzin for tannin or
tannin±protein degrading bacteria that could be used in cattle to improve their utilisation
of browse.
2. Materials and methods
The plant materials listed in Table 1 were grown at the CSIRO, Lansdown
Pasture Research Station, 50 km south of Townsville in tropical north Queensland.
The shrub samples consisted of the ®rst ®ve fully expanded leaves on actively growing
shoots about 1 m long. The grass leaves were plucked from young actively growing
tillers.
Table 1
The tropical forage species used and their nitrogen (N) and condensed tannin (CT) content
Species
Cultivar or CPI no.a
N (%)
Free CT vc
Free CT bc
Total CT bc
Leucaena leucocephala
Leucaena pallida
Leucaena trichandra
Calliandra calothyrsus
Gliricidia sepium
Acacia boliviana
Panicum maximum (grass)
cv. Cunningham
84581
46568
115690
110395
40175
Local
4.04
3.87
3.89
3.50
4.07
4.24
2.97
3.46
2.54
2.54
5.07
0.26
4.32
NDb
5.47
4.65
7.58
5.03
0.01
1.75
ND
6.03
6.72
9.25
5.78
4.07
1.75
ND
a
Commonwealth plant introduction number (Australia).
ND: no CT detected.
c
CT estimated by vanillin/HCl v or butanol/HCl b (Jackson et al., 1996).
b
R.J. Jones et al. / Animal Feed Science and Technology 87 (2000) 287±296
289
The leaves were collected and placed on dry ice, then freeze dried in the laboratory,
ground to pass a 1 mm sieve and stored in sealed bottles in the laboratory. Samples were
analysed for N (Kjeldahl) and condensed tannin (CT) by both the vanillin/HCl and the
butanol/HCl assays (Jackson et al., 1996).
The in-vitro digestions were conducted at the Laboratorio de Fisiologia Gastrointestinal, Centro de Bio®sica y Bioquimica, Instituto Venezolano de Investigaciones
Cienti®cas (IVIC), Caracas, Venezuela. A modi®ed Tilley and Terry (1963) procedure
was used to estimate in-vitro digestibility. In brief, the ®rst fermentation stage was
extended from 48 to 72 h, which reduces variability with tanniniferous feeds, and the
pepsin digestion stage was reduced from 48 to 24 h. In addition to dry matter digestion
((IVDMD), nitrogen digestion (IVND) was also measured by analysing the plant
materials and the residues for N. The method is described in more detail by Jones et al.
(1998).
Crop ¯uid was obtained from four mature birds collected at the Hato Pinero cattle
ranch, Cojedes State, central Venezuela. The birds were captured at night, after their
evening feeding period and brought live to IVIC the following morning. Crops were
removed and the crop contents (which were rather dry compared with rumen contents)
placed in 500 ml of McDougall buffer at 398C. Mixing was done in a blender under CO2,
and the contents were strained through four layers of cheesecloth, added to 2 l of buffer
under CO2 and maintained at 398C.
The rumen ¯uid was obtained from a Holstein cow ®stulated at the rumen. The cow
had grazed tropical pastures at the Central University of Venezuela farm at Maracay. It
was strained through four layers of cheesecloth and 500 ml added to 2 l of buffer as for
the crop ¯uid.
Samples of the forages were weighed (0.25 g) into 50 ml capacity centrifuge tubes to
which was added 1 ml of distilled water or 1 ml of polyethylene glycol 4000 (4 g/100 ml
water) (PEG). Tubes then received 25 ml of either Hoatzin crop ¯uid/buffer (HCF) or cow
rumen ¯uid/buffer (CRF). Tubes were ¯ushed with CO2 during these operations. The
capped tubes were then incubated in an anaerobic chamber for 72 h. Appropriate blank
tubes containing no forage sample were also incubated. There were seven plant
species 2 animal species 2 PEG treatments each in quadruplicate, plus 35 blanks, i.e.
147 tubes in the experiment.
Tubes were swirled three times a day. Caps were loosened to release any pressure each
day. After 3 days the tubes were centrifuged, the supernatant poured off and 25 ml of acid
pepsin solution (4 g/l of 0.1 M HCl) added. Tubes were then incubated at 398C for 24 h,
and swirled three times during this period. They were then centrifuged, the supernatant
discarded and 37.5 ml water at 608C added. Tubes were shaken vigorously and again
centrifuged to wash the samples. The supernatant was discarded and the tubes dried at
1008C for 72 h before weighing. The residues in the tubes were ground in a pestle and
mortar to reduce particle size for estimation of N by a micro-Kjeldahl technique.
Dry matter and N loss was calculated from initial and ®nal weights after correction for
the blank values. These values expressed as a percentage were referred to as IVDMD and
IVND, respectively. The analytical mean data were analysed in the general linear model
package (SPSS) as a factorial layout. The highest order interaction was used as the error
term.
290
R.J. Jones et al. / Animal Feed Science and Technology 87 (2000) 287±296
Table 2
Effect of animal and plant species on the IVDMD (%) of seven tropical foragesa
Plant species
Animal species
Hoatzin
Cow
L. leucocephala
L. pallida
L. trichandra
C. calothyrsus
G. sepium
A. boliviana
P. maximum
48.7
40.0
35.8
33.5
62.6
32.1
30.6
67.3
57.5
61.3
53.6
76.6
47.5
74.2
Mean
40.5
62.6
a
LSD for the animal plant species interaction at P < 0:05 6:08; and at P < 0:01 9:21 (Error
DF 6).
3. Results
The feeds varied in N and CT content. All species except the grass had N contents
higher than 3%. G. sepium had the lowest free CT and L. trichandra the highest as
estimated by the butanol/HCl assay with the other species intermediate. With the vanillin/
HCl assay, G. sepium had again the lowest value and C. calothyrsus the highest (Table 1).
In general, the vanillin/HCl values were lower than the butanol/HCl values but the
notable exception was A. boliviana. For this species, the vanillin/HCl values were far
higher than the butanol/HCl values (Table 1).
Samples inoculated with both CRF and HCF appeared to digest normally with active
fermentation apparent on days 1 and 2. The samples incubated with HCF stopped
digesting some 12 h earlier than did the samples incubated with CRF. The grass sample
was the ®rst to stop with HCF and the last to stop digesting with the CRF.
For IVDMD, plant species and animal species gave signi®cant effects (P < 0:01) as
did PEG (P < 0:05). In addition, the two-way interactions of animal plant species
(Table 2) and animal PEG (Table 3) were also signi®cant (P < 0:01). CRF gave higher
IVDMD than HCF for all feeds, but the response of 44% units with P. maximum was far
Table 3
The effect of animal (Hoatzin and cow) and PEG on the mean IVDMD (%) and mean IVND (%) of seven
tropical foragesa
PEG treatment
No PEG
Plus 160 mg PEG/g DM
a
IVDMD (%)
IVND (%)
Hoatzin
Cow
Hoatzin
Cow
37.4
43.5
63.0
62.1
26.5
51.9
75.6
83.4
LSD for the interaction at P < 0:01 for IVDMD 4:92 (Error DF 6) and at P < 0:05 5:86; P < 0:01
for IVND 8:88 (Error DF 6).
291
R.J. Jones et al. / Animal Feed Science and Technology 87 (2000) 287±296
greater than with the other feeds (P < 0:01) (Table 2). There was no signi®cant effect of
PEG on IVDMD with CRF but a highly signi®cant (P < 0:01) improvement with HCF
(Table 3).
Overall, the IVDMD with CRF was 22% units higher than with HCF (P < 0:01). There
was a positive response to PEG with HCF of about 6 units overall. The grass was very
well digested by CRF (74%) but very poorly digested by HCF (30%) (P < 0:01). In the
absence of PEG, the relation between IVDMD with CRF and HCF was poor (r2 0:407)
mainly because of two species (Panicum maximum and Acacia boliviana). Omitting these
values resulted in a good relation (r 2 0:867). In the presence of PEG, only one species,
P. maximum, departed from a linear relation between CRF and HCF. Omitting this species
resulted in an excellent relation between IVDMD values obtained with CRF and HCF
(r 2 0:954) (Fig. 1).
The differences between shrub species were large (P < 0:01) (Table 2). Of the shrub
legumes, G. sepium had the highest IVDMD with both inoculum sources and A. boliviana
had the lowest digestibility. Overall the ranking of the shrubs at P 0:05 was
G:sepium > L:leucocephala > P:maximum > L:pallida L:trichandra > C:calothyrsus
> A:boliviana.
For IVND, the effects of PEG (51.7 v 67.6%; P < 0:001) and animal species (79.5 v
39.2%; P < 0:001) were far greater than for IVDMD. In addition, the animal PEG
(Table 3) and the PEG plant species (Table 4) interactions were also signi®cant
(P < 0:01±0.02), but the animal plant species interaction was not signi®cant
(P > 0:05). In the absence of PEG, the HCF gave very low IVND values for all feeds
(Table 3). In the presence of PEG, IVND was almost doubled, whereas for the CRF,
IVND increased only by about 10% with PEG (Table 3). With both inoculum sources,
PEG had little effect on the IVND of Panicum maximum which contains no tannins
(Table 4). However, with HRF the mean IVND was only about 30% compared with 80%
for CRF. A. boliviana and C. calothyrsus gave IVND values
87 (2000) 287±296
Short communication
Comparison of the digestive ability of crop ¯uid
from the folivorous Hoatzin (Opisthocomus hoazin)
and cow rumen ¯uid with seven tropical forages
R.J. Jonesa,*, M.A. Garcia Amadob, M.G. Dominguez-Bellob
a
CSIRO Davies Laboratory, PMB, Post Of®ce, Aitkenvale, Townsville, Qld. 4814, Australia
Centro de BiofõÂsica y BiochõÂmica, Instituto de Investigaciones Cientõ®cas (IVIC), Caracas, Venezuela
b
Received 5 October 1999; received in revised form 14 June 2000; accepted 10 August 2000
Abstract
We explored the hypothesis that the Hoatzin, a tropical bird which feeds on tree leaves and has a
crop resembling a rumen, may have a better ability to digest tanniniferous feeds than do cattle.
Comparisons were made between Hoatzin crop ¯uid (HCF) and cow rumen ¯uid (CRF) in in-vitro
digestion studies using freeze dried leaves of six tropical tanniniferous shrub legumes and the
tropical grass Panicum maximum. In-vitro dry matter digestibility (IVDMD) and in-vitro nitrogen
digestibility (IVND) were measured in the presence and absence of polyethylene glycol (PEG) to
minimise the effect of condensed tannin.
For all plant species, and in the presence or absence of PEG, the CRF gave higher IVDMD and
IVND than did HCF (P < 0:01). The interaction of PEG animal (P < 0:01) for IVDMD was due
to an absence of response with CRF (62.1 v 63.0%) and a large response with HCF (43.5 v 37.4%).
Similarly for IVND, the response to PEG with CRF was much smaller (83.4 v 75.6%) than for HCF
(51.9 v 26.5%) (P < 0:01).
PEG had no signi®cant effect on IVDMD or IVND of the CT-free Panicum maximum by HCF or
CRF (P > 0:05). However, values were much higher with CRF: 74.2 v 30.6% and 81.3 v 29.0%,
respectively.
The only legume to have reasonable levels (>55%) of IVDMD and IVND with HCF in the
absence of PEG was Gliricidia sepium, which has little or no free condensed tannins. Acacia
boliviana, Calliandra calothyrsus and Leucaena trichandra gave low values and those for L.
leucocephala and L. pallida were intermediate.
The low IVDMD and IVND with HCF, together with the large response to PEG, clearly show
that high tannin content in the diet cannot be handled by the Hoatzin. Low tannin content in the
crop contents indicates that it avoids highly tanniniferous leaves. This supports other ®ndings that
the Hoatzin is extremely selective of a high quality leafy diet.
*
Corresponding author. Tel.: 61-747538500; fax: 61-747538600.
E-mail address: raymond.jones@tag.csiro.au (R.J. Jones).
0377-8401/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 3 7 7 - 8 4 0 1 ( 0 0 ) 0 0 1 9 9 - 1
288
R.J. Jones et al. / Animal Feed Science and Technology 87 (2000) 287±296
It is concluded that the Hoatzin is an unlikely source of bacteria to improve the feeding value of
tropical tanniniferous shrub legumes for cattle. # 2000 Elsevier Science B.V. All rights reserved.
Keywords: Tanniniferous shrubs; Condensed tannins; In-vitro digestibility; Foregut fermentation; Hoatzin
1. Introduction
The Hoatzin (Opisthocomus hoazin) is a folivorous bird native to areas of South
America. It is unique in having a digestion pattern similar to that in ruminants (Grajal
et al., 1989). It feeds on the leaves of many riverine tree species. These trees belong to
plant families known to have a variety of toxic principles. Among these toxic compounds
are phenols and tannins (Dominguez-Bello et al., 1994). It has been hypothesised that
these birds may have the ability to detoxify these antinutritive compounds by its foregut
fermentation.
In this paper, we examine this hypothesis by comparing the digestion in-vitro of several
tropical tanniniferous browse species which are being evaluated for cattle production in
Australia. The aim of the work was to assess the potential of the Hoatzin for tannin or
tannin±protein degrading bacteria that could be used in cattle to improve their utilisation
of browse.
2. Materials and methods
The plant materials listed in Table 1 were grown at the CSIRO, Lansdown
Pasture Research Station, 50 km south of Townsville in tropical north Queensland.
The shrub samples consisted of the ®rst ®ve fully expanded leaves on actively growing
shoots about 1 m long. The grass leaves were plucked from young actively growing
tillers.
Table 1
The tropical forage species used and their nitrogen (N) and condensed tannin (CT) content
Species
Cultivar or CPI no.a
N (%)
Free CT vc
Free CT bc
Total CT bc
Leucaena leucocephala
Leucaena pallida
Leucaena trichandra
Calliandra calothyrsus
Gliricidia sepium
Acacia boliviana
Panicum maximum (grass)
cv. Cunningham
84581
46568
115690
110395
40175
Local
4.04
3.87
3.89
3.50
4.07
4.24
2.97
3.46
2.54
2.54
5.07
0.26
4.32
NDb
5.47
4.65
7.58
5.03
0.01
1.75
ND
6.03
6.72
9.25
5.78
4.07
1.75
ND
a
Commonwealth plant introduction number (Australia).
ND: no CT detected.
c
CT estimated by vanillin/HCl v or butanol/HCl b (Jackson et al., 1996).
b
R.J. Jones et al. / Animal Feed Science and Technology 87 (2000) 287±296
289
The leaves were collected and placed on dry ice, then freeze dried in the laboratory,
ground to pass a 1 mm sieve and stored in sealed bottles in the laboratory. Samples were
analysed for N (Kjeldahl) and condensed tannin (CT) by both the vanillin/HCl and the
butanol/HCl assays (Jackson et al., 1996).
The in-vitro digestions were conducted at the Laboratorio de Fisiologia Gastrointestinal, Centro de Bio®sica y Bioquimica, Instituto Venezolano de Investigaciones
Cienti®cas (IVIC), Caracas, Venezuela. A modi®ed Tilley and Terry (1963) procedure
was used to estimate in-vitro digestibility. In brief, the ®rst fermentation stage was
extended from 48 to 72 h, which reduces variability with tanniniferous feeds, and the
pepsin digestion stage was reduced from 48 to 24 h. In addition to dry matter digestion
((IVDMD), nitrogen digestion (IVND) was also measured by analysing the plant
materials and the residues for N. The method is described in more detail by Jones et al.
(1998).
Crop ¯uid was obtained from four mature birds collected at the Hato Pinero cattle
ranch, Cojedes State, central Venezuela. The birds were captured at night, after their
evening feeding period and brought live to IVIC the following morning. Crops were
removed and the crop contents (which were rather dry compared with rumen contents)
placed in 500 ml of McDougall buffer at 398C. Mixing was done in a blender under CO2,
and the contents were strained through four layers of cheesecloth, added to 2 l of buffer
under CO2 and maintained at 398C.
The rumen ¯uid was obtained from a Holstein cow ®stulated at the rumen. The cow
had grazed tropical pastures at the Central University of Venezuela farm at Maracay. It
was strained through four layers of cheesecloth and 500 ml added to 2 l of buffer as for
the crop ¯uid.
Samples of the forages were weighed (0.25 g) into 50 ml capacity centrifuge tubes to
which was added 1 ml of distilled water or 1 ml of polyethylene glycol 4000 (4 g/100 ml
water) (PEG). Tubes then received 25 ml of either Hoatzin crop ¯uid/buffer (HCF) or cow
rumen ¯uid/buffer (CRF). Tubes were ¯ushed with CO2 during these operations. The
capped tubes were then incubated in an anaerobic chamber for 72 h. Appropriate blank
tubes containing no forage sample were also incubated. There were seven plant
species 2 animal species 2 PEG treatments each in quadruplicate, plus 35 blanks, i.e.
147 tubes in the experiment.
Tubes were swirled three times a day. Caps were loosened to release any pressure each
day. After 3 days the tubes were centrifuged, the supernatant poured off and 25 ml of acid
pepsin solution (4 g/l of 0.1 M HCl) added. Tubes were then incubated at 398C for 24 h,
and swirled three times during this period. They were then centrifuged, the supernatant
discarded and 37.5 ml water at 608C added. Tubes were shaken vigorously and again
centrifuged to wash the samples. The supernatant was discarded and the tubes dried at
1008C for 72 h before weighing. The residues in the tubes were ground in a pestle and
mortar to reduce particle size for estimation of N by a micro-Kjeldahl technique.
Dry matter and N loss was calculated from initial and ®nal weights after correction for
the blank values. These values expressed as a percentage were referred to as IVDMD and
IVND, respectively. The analytical mean data were analysed in the general linear model
package (SPSS) as a factorial layout. The highest order interaction was used as the error
term.
290
R.J. Jones et al. / Animal Feed Science and Technology 87 (2000) 287±296
Table 2
Effect of animal and plant species on the IVDMD (%) of seven tropical foragesa
Plant species
Animal species
Hoatzin
Cow
L. leucocephala
L. pallida
L. trichandra
C. calothyrsus
G. sepium
A. boliviana
P. maximum
48.7
40.0
35.8
33.5
62.6
32.1
30.6
67.3
57.5
61.3
53.6
76.6
47.5
74.2
Mean
40.5
62.6
a
LSD for the animal plant species interaction at P < 0:05 6:08; and at P < 0:01 9:21 (Error
DF 6).
3. Results
The feeds varied in N and CT content. All species except the grass had N contents
higher than 3%. G. sepium had the lowest free CT and L. trichandra the highest as
estimated by the butanol/HCl assay with the other species intermediate. With the vanillin/
HCl assay, G. sepium had again the lowest value and C. calothyrsus the highest (Table 1).
In general, the vanillin/HCl values were lower than the butanol/HCl values but the
notable exception was A. boliviana. For this species, the vanillin/HCl values were far
higher than the butanol/HCl values (Table 1).
Samples inoculated with both CRF and HCF appeared to digest normally with active
fermentation apparent on days 1 and 2. The samples incubated with HCF stopped
digesting some 12 h earlier than did the samples incubated with CRF. The grass sample
was the ®rst to stop with HCF and the last to stop digesting with the CRF.
For IVDMD, plant species and animal species gave signi®cant effects (P < 0:01) as
did PEG (P < 0:05). In addition, the two-way interactions of animal plant species
(Table 2) and animal PEG (Table 3) were also signi®cant (P < 0:01). CRF gave higher
IVDMD than HCF for all feeds, but the response of 44% units with P. maximum was far
Table 3
The effect of animal (Hoatzin and cow) and PEG on the mean IVDMD (%) and mean IVND (%) of seven
tropical foragesa
PEG treatment
No PEG
Plus 160 mg PEG/g DM
a
IVDMD (%)
IVND (%)
Hoatzin
Cow
Hoatzin
Cow
37.4
43.5
63.0
62.1
26.5
51.9
75.6
83.4
LSD for the interaction at P < 0:01 for IVDMD 4:92 (Error DF 6) and at P < 0:05 5:86; P < 0:01
for IVND 8:88 (Error DF 6).
291
R.J. Jones et al. / Animal Feed Science and Technology 87 (2000) 287±296
greater than with the other feeds (P < 0:01) (Table 2). There was no signi®cant effect of
PEG on IVDMD with CRF but a highly signi®cant (P < 0:01) improvement with HCF
(Table 3).
Overall, the IVDMD with CRF was 22% units higher than with HCF (P < 0:01). There
was a positive response to PEG with HCF of about 6 units overall. The grass was very
well digested by CRF (74%) but very poorly digested by HCF (30%) (P < 0:01). In the
absence of PEG, the relation between IVDMD with CRF and HCF was poor (r2 0:407)
mainly because of two species (Panicum maximum and Acacia boliviana). Omitting these
values resulted in a good relation (r 2 0:867). In the presence of PEG, only one species,
P. maximum, departed from a linear relation between CRF and HCF. Omitting this species
resulted in an excellent relation between IVDMD values obtained with CRF and HCF
(r 2 0:954) (Fig. 1).
The differences between shrub species were large (P < 0:01) (Table 2). Of the shrub
legumes, G. sepium had the highest IVDMD with both inoculum sources and A. boliviana
had the lowest digestibility. Overall the ranking of the shrubs at P 0:05 was
G:sepium > L:leucocephala > P:maximum > L:pallida L:trichandra > C:calothyrsus
> A:boliviana.
For IVND, the effects of PEG (51.7 v 67.6%; P < 0:001) and animal species (79.5 v
39.2%; P < 0:001) were far greater than for IVDMD. In addition, the animal PEG
(Table 3) and the PEG plant species (Table 4) interactions were also signi®cant
(P < 0:01±0.02), but the animal plant species interaction was not signi®cant
(P > 0:05). In the absence of PEG, the HCF gave very low IVND values for all feeds
(Table 3). In the presence of PEG, IVND was almost doubled, whereas for the CRF,
IVND increased only by about 10% with PEG (Table 3). With both inoculum sources,
PEG had little effect on the IVND of Panicum maximum which contains no tannins
(Table 4). However, with HRF the mean IVND was only about 30% compared with 80%
for CRF. A. boliviana and C. calothyrsus gave IVND values