Directory UMM :Data Elmu:jurnal:A:Animal Feed Science and Technology:Vol82.Issue1-2.Nov1999:
Animal Feed Science and Technology
82 (1999) 63±73
Nutritional uniformity of neutral detergent solubles
in some tropical browse leaf and pod diets
C.M. Shayoa,*, P. UdeÂnb
a
Zonal Research and Training Centre, Livestock Production Research Institute,
P.O. Box 202, Mpwapwa, Tanzania
b
Department of Animal Nutrition and Management, Swedish University of Agricultural Sciences,
P.O. Box 7024, S-750 07, Uppsala, Sweden
Received 7 September 1998; received in revised form 17 June 1999; accepted 20 July 1999
Abstract
An experiment was conducted to study the nutritional uniformity of neutral detergent solubles
(NDS) in tropical browse species comprising Faidherbia albida, Acacia tortilis, Delonix elata and
Mulberry (Morus alba) leaves and F. albida, A. tortilis, A. nilotica and Dichrostachys cinerea pods.
The browse supplements were fed together with maize bran to individually caged goats at
increasing levels in hay-based diets. Each diet had five levels of the browse feeds in duplicate which
were randomly allocated to the goats in five periods of 14 days each. Chemical composition of the
feeds consumed and faeces voided were determined. Nutritional uniformity (Lucas test) of NDS
was determined for individual browse by regressing the digestible amount upon its content in the
dry matter, in which the regression slope represents true digestibility and the y-intercept,
endogenous excretions.
A. nilotica pods and A. tortilis and D. elata leaves were not well accepted by the animals, due to the
high levels of phenolic compounds and mould. There was no significant (p > 0.05) relationship
between the estimated amount of digested NDS and content of phenolic compounds in the browses.
True digestibilities of NDS were significantly (p < 0.05) different between the species. The yintercepts were not significantly (p > 0.05) different from zero for all species except F. albida leaves
(ÿ7.89). The true digestibility (SD) of NDS for all the species combined in the Lucas test was 91.9
0.03% and the metabolic matter was estimated at 3.38 1.13 g/100 g of dry matter intake. The
variable true NDS digestibility among the species was an indication of non-uniformity of this fraction,
implying that the digestibility of the NDS fraction of tropical browse species may not be predicted
from its content. Further studies to include more species are necessary to determine if this is a general
phenomenon with tropical browse species. # 1999 Elsevier Science B.V. All rights reserved.
Keywords: Tropical browse; Digestibility; Neutral detergent solubles; Lucas/uniformity test
*
Corresponding author.
0377-8401/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved.
PII: S 0 3 7 7 - 8 4 0 1 ( 9 9 ) 0 0 0 9 8 - X
64
C.M. Shayo, P. UdeÂn / Animal Feed Science and Technology 82 (1999) 63±73
1. Introduction
The use of simple laboratory methods that can predict nutritive value by the content of
nutrients in the forages is of great practical and economic importance. According to
Lucas (1964), a rational system of feed analysis could be developed if feed fractions
could be found for which the indigestible or digestible amounts could be predicted from
their composition. A reliable prediction of the digestible amount will depend on the
uniform availability of the nutrient fraction in question. A feed fraction which has the
same true digestibility irrespective of level and origin is considered nutritionally uniform
(Van Soest, 1994) and may be estimated by the Lucas equation (Lucas, 1964), in which
the digestible fraction per unit of the feed is regressed upon its concentration in the feed.
The regression slope in the Lucas test represents true digestibility and the intercept,
endogenous excretions.
The neutral detergent soluble fraction of feeds is considered to be completely available
(Van Soest, 1994). However, the NDS fraction is comprised of sugars, soluble
carbohydrates, pectins, non-protein nitrogen, proteins, lipids and other solubles (Van
Soest, 1994), some of which (e.g. proteins and carbohydrates) may react with tannins
to form unavailable complexes (Nastis and Malechek, 1981; Zucker, 1983). A high
proportion of the phenolics is also soluble in neutral detergent reagent, and therefore may
not be digested by the animal. Tannins occur in many browse species (Reed et al.,
1985; Reed, 1986; Mueller-Harvey et al., 1987), and can result in non-uniformity
of the NDS fraction. To confirm this, an in vivo study was conducted with some browse
leaves and pods.
2. Materials and methods
2.1. Animals and feeds
The trial was conducted at the Livestock Production Research Institute, Mpwapwa, in
central Tanzania using 16 male goats weighing between 14 and 32 kg (mean 20.8 kg).
Prior to commencement of the experiment, all goats were sprayed against ectoparasites
and drenched against endoparasites. Initially, 14 days were allowed for the animals to
become acclimatised to the test feeds. The diets were comprised of hay and
supplements. The supplements consisted of maize bran (MB) and browse leaves or
pods. The browse leaves came from Faidherbia albida, Acacia tortilis, Delonix elata
and mulberry (Morus alba) trees, and the pods were from F. albida, A. tortilis, A. nilotica
and Dichrostachys cinerea trees. A. nilotica pods, and A. tortilis and D. elata leaves
were harvested two years before they were used in this study, whereas the other
browse supplements were harvested and stored for a period of less than six months.
The hay comprised mainly Rhodes grass (Chloris gayana), Cynodon spp and Buffel
grass (Cenchrus ciliaris). Incorporation of maize bran was necessary as the goats
would otherwise not consume some of the supplements, particularly the ground pods
if fed alone. Each diet had five levels of the browse feeds in duplicate and they
were randomly allocated to the goats in five periods. Except for Level 0, MB formed
C.M. Shayo, P. UdeÂn / Animal Feed Science and Technology 82 (1999) 63±73
65
Table 1
Daily amount of feedstuffs offered to goats
Level
Browse
Maize bran
Hay
Total
2.5
2.5
5.0
7.5
10.0
45.0
39.0
30.0
21.0
12.0
47.5
46.5
45.0
43.5
42.0
(g/kg BW)
a
0
1
2
3
4
0
5.0
10.0
15.0
20.0
a
This level was excluded from further analyses.
50% of the amount of the browse offered. Level 0 had a small amount of MB, which
should not have been included. Daily amount of the supplements (maize bran browse)
in each level was calculated based on the animal's body weight (BW), and were 7.5,
15, 22.5 and 30 g/kg of the animals' BW for levels 1, 2, 3, and 4, respectively. Hay
offered was calculated such that total feed offered (supplements hay) would make up to
40 g/kg BW per day plus an allowance of 20% of hay as refusals. The goats were
randomly allocated to the treatments in an unbalanced design and were not blocked
for weight. It was assumed that differences in goat weight would not result in a
significant variation in the digestibility of a particular feed type. Actual amounts (g/kg
BW) of hay, maize bran and browse supplements provided are shown in Table 1.
Although the diets in Level 0 were offered through out the trial, the values for these
were excluded from analyses.
2.2. Feeding and data collection
After the acclimatisation period, the goats were fitted with faecal collection bags
and caged individually. During the 14-day experimental period, the goats were
provided with hay and the supplements (treatments). In each experimental period, there
was a preliminary period of seven days, followed by seven days of data collection, and
between each experimental period the animals were removed from the cages for 10 days.
Water and mineral block were accessible to the animals throughout the experimental
period. Each morning, at 8.00 h, the animals were provided with the test diets. The pods
and the MB were fed in a mixture, whereas the leaves and the MB were fed separately,
starting with MB followed by the leaves. Hay was provided immediately after
consumption of the test feeds. However, some supplements were not completely
consumed even after 6 h. Refused supplements were removed at 14.00 h, weighed, and
the animals provided with hay. Each morning, at 7.30 h, hay refusals from the previous
day for each animal were removed and weighed. About 10% of the refusals were
sub-sampled for dry matter (DM), organic matter (OM) and neutral detergent fibre
(NDF). Faeces were collected in the bags attached to the rear of the animal. Faecal
collection bags were emptied twice a day during the data collection period, weighed and
10% deep frozen for laboratory analyses.
66
C.M. Shayo, P. UdeÂn / Animal Feed Science and Technology 82 (1999) 63±73
2.3. Laboratory analyses
DM, ash and CP contents of the feed samples and faeces were determined according to
the procedures of AOAC (1985), and NDF and acid detergent fibre (ADF) according to
Van Soest et al. (1991). The neutral detergent soluble fraction (NDS) was calculated on
OM basis and hemicellulose (Hem) was calculated as the difference between NDF and
ADF. Total phenolics were determined by the Folin±Ciocalteu method as described by
Waterman and Mole (1994). The extract was further diluted to 0.1 mg DM/ml.
Absorbance was read at 740 nm through a 1-cm cuvette.
2.4. Mathematical analyses
The true digestibilities of the NDS fraction and the metabolic contributions for
individual diets and all the diets combined were determined by regressing the digested
amount of NDS upon its percentage in the DM (Lucas, 1964).
The estimated true digestibilities were compared using a one-way analysis of variance
for differences between the species. For the species which showed significant differences,
the means were compared using Tukey's procedure at p < 0.05. To establish whether the
content of phenolic compounds had influenced NDS digestibility, the estimated true
digestibility of NDS for individual species was regressed upon the content of phenolic
compounds.
2.5. Results and discussion
The chemical compositions of the feeds used in the present study are shown in
Table 2. Except for F. albida and D. elata leaves, which had about 20% of CP, the
Table 2
Chemical composition of the feedstuffs offered to goatsa
Feedstuff
Ash
(% of DM)
CP
(% of OM)
NDF
NDS
ADF
Hem
Mulberry leaves
Acacia tortilis pods
Faidherbia albida pods
F. albida leaves
Dichrostachys cinerea pods
A. nilotica pods
Delonix elata leaves
A. tortilis leaves
Maize bran
Hay
12.8
5.9
4.4
5.5
6.3
5.8
7.5
6.4
2.7
5.7
13.2
14.1
11.8
19.2
10.4
10.7
21.6
12.8
10.1
2.8
23.5
31.8
36.2
35.4
40.4
22.2
52.9
45.6
33.4
73.5
63.7
62.3
59.4
59.1
53.3
72.0
39.6
48.0
63.9
15.4
20.4
26.6
28.8
25.3
32.5
17.2
31.1
43.1
8.7
49.4
3.1
5.2
7.4
10.1
7.9
4.6
21.8
2.5
24.7
24.1
Total soluble
phenolicsb
(740 nm)
32.8
53.8
79.3
46.8
106.8
294.8
108.7
118.2
nac
na
a
CP, crude protein; NDF, neutral detergent fibre; NDS, neutral detergent solubles; ADF, acid detergent fibre;
and Hem, hemicellulose.
b
Total soluble phenolic compounds presented as absorbance at 740 nm (units/100 mg DM/ml extract).
c
Not available.
C.M. Shayo, P. UdeÂn / Animal Feed Science and Technology 82 (1999) 63±73
67
other supplements had moderate values (10±14%). However, the CP content of the
browse species were higher than CP content in the basal diet in most grasses,
particularly during the dry season (Gupta and Pradhan, 1975). Despite the high CP
content, A. nilotica pods and A. tortilis and D. cinerea leaves were not well accepted by
the animals. In many cases, the animals could not completely consume the amounts
offered even after 6 h. Ground A. nilotica > pods formed a `gum-like' material in the
mouths of the goats which seemed to reduce intake. The other supplements were
completely consumed. Generally, ground pods took a longer time to finish as compared
with leaves.
Since the indigenous browse species have co-evolved with predator populations of
insects, bacteria, fungi and grazing animals they have developed defence mechanisms,
such as chemical defence, which can be deterrent, toxic or reduce intake and digestibility.
Tannins are known to reduce intake by various herbivores (Coley et al., 1985; Cooper and
Owen-Smith, 1985; Ahn et al., 1989). A. nilotica pods and A. tortilis and D. elata leaves
contained higher levels of phenolic compounds than the other browse species (except D.
cinerea pods) and this could have been one of the reasons for their low intakes. There
have been some studies also showing that intakes of A. nilotica pods by cattle, sheep and
goats were lower than in pods of other browse species containing lower levels of phenolic
compounds (Tanner et al., 1990; Shayo and UdeÂn, 1998). The low acceptance of A.
tortilis and D. elata leaves could also have been a result of mould developed on the leaves
during storage, as they were harvested two years before they were used in this study.
However, this was not the case in a study by Omar et al. (1998), who did not find any
reduced intake of mouldy mulberry leaves by goats, which could probably be an
indication that mould type may also be a factor.
The supplements had considerably higher NDS concentrations than the basal diet,
resulting in an increase in the NDS content of the diet with level of supplementation
(Table 3).
Relationships between the digested amount of NDS and its amount in the DM
consumed (Lucas test) for individual species and for all species combined are shown in
Table 4 and Fig. 1. However, A. nilotica pods, and A. tortilis and D. elata leaves were not
considered in this aspect due to their low and inconsistent intakes.
The slopes of the regression equations in the Lucas test, which are estimates of
the true digestibilities of NDS, were significantly (p < 0.05) different among the species.
Table 3
Mean NDS (% of DM) in the browse, maize bran and hay diets consumed by goats
Level
1
2
3
4
a
Feed
Total
hay
maize bran
browse
16.7
12.8
8.7
4.7
4.2
8.2
12.3
16.5
7.8
15.3
23.1
30.8
Mean of all the browse species.
a
28.7
36.3
44.2
52.0
68
C.M. Shayo, P. UdeÂn / Animal Feed Science and Technology 82 (1999) 63±73
Table 4
Relationship between the digestible amount of the neutral detergent solubles (NDS) and increasing amount in
the dry matter of some tropical browse species by goats on maize bran and hay based diets
Species
Faidherbia albida pods
Acacia tortilis pods
Dichrostachys cinerea pods
F. albida leaves
Mulberry leaves
All species combined
a
Slopea
0.781a
0.968c
0.860b
1.042d
0.883b
0.919
Intercept
1.76
ÿ4.76
ÿ1.71
ÿ7.89
ÿ2.33
ÿ3.38
R2 (%)
95.8
98.6
98.2
98.9
98.0
96.9
Standard deviation
intercept
slope
residual
2.91
1.98
1.87
2.09
2.15
1.13
0.073
0.047
0.048
0.050
0.051
0.027
1.68
1.18
1.02
1.22
1.32
1.49
Values in the same column followed by different letters are significantly different (p < 0.05).
Feed fractions showing variable digestibilities are regarded to be non-ideal (Van
Soest, 1994). Although the NDS fraction of feeds is regarded as being almost completely available (Van Soest, 1994), the variability of the NDS fraction in the feeds
tested could have been due to the effect of tannins, since they can react with
carbohydrates, enzymes and proteins of the feeds to form indigestible complexes
(Hagerman et al., 1992; Reed and Soller, 1987; Robbins et al., 1987). According to Reed
et al. (1990), most complexes formed are not soluble in neutral detergent. As the
complexes are recovered in the NDF fraction of the faeces, the proportion of NDS in the
faeces is reduced, and thus the true digestibility value of the NDS is overestimated.
Therefore, the presence of tannins in the diet may result in an elevated slope in the
Lucas test. Reed et al. (1990) found that nitrogen in some tropical browse species was
not nutritionally uniform due to the presence of tannins. However, the degree of
precipitation of proteins depends on molecular weight and reactivity rather than
content of the tannins (Kumar, 1983; Makkar et al., 1990; Hagerman et al., 1992).
Probably, it is in this context that there was no significant (p > 0.05) relationship between
the content of phenolic compounds in the feeds and the estimated true digestibility of
the NDS fraction.
The findings in this study are in contrast with those of Van Soest (1967), Seoane
(1982), Laforest et al. (1986) and Christen et al. (1990), who reported that NDS in some
temperate legume and grass hays and silages were nutritionally uniform. However, in
another Lucas test with some temperate grass and legume hays Aerts et al. (1978)
did not find the cell contents to be nutritionally uniform. The authors obtained
true digestibility values much greater than 100% and suggested that this might have
resulted from increasing true digestibility of cell contents with increasing percentage
of cell contents, or from a decrease of metabolic matter with increasing percentage of
cell contents, or both.
In the present study, the metabolic amounts estimated from the Lucas test for the
individual species except F. albida leaves were not significantly (p > 0.05) different from
zero. The average metabolic fraction was lower (3.4 g/100 g of DM intake) than that
reported by Van Soest (1967), Aerts et al. (1978), Laforest et al. (1986), Seoane (1982)
C.M. Shayo, P. UdeÂn / Animal Feed Science and Technology 82 (1999) 63±73
69
Fig. 1. Test of nutritional uniformity of neutral detergent soluble fraction in Faidherbia albida pods (a), Acacia
tortilis pods (b), Dichrostachys cinerea pods (c), F. albida leaves (d), mulberry leaves (e) and all the species
combined (f). SDa, standard deviation of the constant; SDb, standard deviation of the regression slope; RSD,
residual standard deviation.
and Christen et al. (1990) of 12.9, 17.0-23.8, 6.6, 12.7 and 13.3 g/100 g of DM intake,
respectively. The reason for this difference is not clear.
3. Conclusions
This study has shown that NDS in some tropical browse is not a nutritionally
uniform entity, suggesting that digestibility of the NDS fraction in tropical browse species
70
C.M. Shayo, P. UdeÂn / Animal Feed Science and Technology 82 (1999) 63±73
Fig. 1 (Continued )
may not be predicted from its content. However, to confirm this, further work with
more species is necessary to determine if this is a general phenomenon with tropical
browse species.
Acknowledgements
The financial support of the Swedish Agency for Research Cooperation with
Developing Countries (SAREC) is gratefully acknowledged. Messrs Anthony Mbeho,
C.M. Shayo, P. UdeÂn / Animal Feed Science and Technology 82 (1999) 63±73
71
Fig. 1 (Continued )
Rehema Kasiga, Helina Nhonya and Hamisi Bakari of the Livestock Production Research
Institute, Mpwapwa, Tanzania, are thanked for their assistance in maintaining the animals
and for laboratory analyses.
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82 (1999) 63±73
Nutritional uniformity of neutral detergent solubles
in some tropical browse leaf and pod diets
C.M. Shayoa,*, P. UdeÂnb
a
Zonal Research and Training Centre, Livestock Production Research Institute,
P.O. Box 202, Mpwapwa, Tanzania
b
Department of Animal Nutrition and Management, Swedish University of Agricultural Sciences,
P.O. Box 7024, S-750 07, Uppsala, Sweden
Received 7 September 1998; received in revised form 17 June 1999; accepted 20 July 1999
Abstract
An experiment was conducted to study the nutritional uniformity of neutral detergent solubles
(NDS) in tropical browse species comprising Faidherbia albida, Acacia tortilis, Delonix elata and
Mulberry (Morus alba) leaves and F. albida, A. tortilis, A. nilotica and Dichrostachys cinerea pods.
The browse supplements were fed together with maize bran to individually caged goats at
increasing levels in hay-based diets. Each diet had five levels of the browse feeds in duplicate which
were randomly allocated to the goats in five periods of 14 days each. Chemical composition of the
feeds consumed and faeces voided were determined. Nutritional uniformity (Lucas test) of NDS
was determined for individual browse by regressing the digestible amount upon its content in the
dry matter, in which the regression slope represents true digestibility and the y-intercept,
endogenous excretions.
A. nilotica pods and A. tortilis and D. elata leaves were not well accepted by the animals, due to the
high levels of phenolic compounds and mould. There was no significant (p > 0.05) relationship
between the estimated amount of digested NDS and content of phenolic compounds in the browses.
True digestibilities of NDS were significantly (p < 0.05) different between the species. The yintercepts were not significantly (p > 0.05) different from zero for all species except F. albida leaves
(ÿ7.89). The true digestibility (SD) of NDS for all the species combined in the Lucas test was 91.9
0.03% and the metabolic matter was estimated at 3.38 1.13 g/100 g of dry matter intake. The
variable true NDS digestibility among the species was an indication of non-uniformity of this fraction,
implying that the digestibility of the NDS fraction of tropical browse species may not be predicted
from its content. Further studies to include more species are necessary to determine if this is a general
phenomenon with tropical browse species. # 1999 Elsevier Science B.V. All rights reserved.
Keywords: Tropical browse; Digestibility; Neutral detergent solubles; Lucas/uniformity test
*
Corresponding author.
0377-8401/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved.
PII: S 0 3 7 7 - 8 4 0 1 ( 9 9 ) 0 0 0 9 8 - X
64
C.M. Shayo, P. UdeÂn / Animal Feed Science and Technology 82 (1999) 63±73
1. Introduction
The use of simple laboratory methods that can predict nutritive value by the content of
nutrients in the forages is of great practical and economic importance. According to
Lucas (1964), a rational system of feed analysis could be developed if feed fractions
could be found for which the indigestible or digestible amounts could be predicted from
their composition. A reliable prediction of the digestible amount will depend on the
uniform availability of the nutrient fraction in question. A feed fraction which has the
same true digestibility irrespective of level and origin is considered nutritionally uniform
(Van Soest, 1994) and may be estimated by the Lucas equation (Lucas, 1964), in which
the digestible fraction per unit of the feed is regressed upon its concentration in the feed.
The regression slope in the Lucas test represents true digestibility and the intercept,
endogenous excretions.
The neutral detergent soluble fraction of feeds is considered to be completely available
(Van Soest, 1994). However, the NDS fraction is comprised of sugars, soluble
carbohydrates, pectins, non-protein nitrogen, proteins, lipids and other solubles (Van
Soest, 1994), some of which (e.g. proteins and carbohydrates) may react with tannins
to form unavailable complexes (Nastis and Malechek, 1981; Zucker, 1983). A high
proportion of the phenolics is also soluble in neutral detergent reagent, and therefore may
not be digested by the animal. Tannins occur in many browse species (Reed et al.,
1985; Reed, 1986; Mueller-Harvey et al., 1987), and can result in non-uniformity
of the NDS fraction. To confirm this, an in vivo study was conducted with some browse
leaves and pods.
2. Materials and methods
2.1. Animals and feeds
The trial was conducted at the Livestock Production Research Institute, Mpwapwa, in
central Tanzania using 16 male goats weighing between 14 and 32 kg (mean 20.8 kg).
Prior to commencement of the experiment, all goats were sprayed against ectoparasites
and drenched against endoparasites. Initially, 14 days were allowed for the animals to
become acclimatised to the test feeds. The diets were comprised of hay and
supplements. The supplements consisted of maize bran (MB) and browse leaves or
pods. The browse leaves came from Faidherbia albida, Acacia tortilis, Delonix elata
and mulberry (Morus alba) trees, and the pods were from F. albida, A. tortilis, A. nilotica
and Dichrostachys cinerea trees. A. nilotica pods, and A. tortilis and D. elata leaves
were harvested two years before they were used in this study, whereas the other
browse supplements were harvested and stored for a period of less than six months.
The hay comprised mainly Rhodes grass (Chloris gayana), Cynodon spp and Buffel
grass (Cenchrus ciliaris). Incorporation of maize bran was necessary as the goats
would otherwise not consume some of the supplements, particularly the ground pods
if fed alone. Each diet had five levels of the browse feeds in duplicate and they
were randomly allocated to the goats in five periods. Except for Level 0, MB formed
C.M. Shayo, P. UdeÂn / Animal Feed Science and Technology 82 (1999) 63±73
65
Table 1
Daily amount of feedstuffs offered to goats
Level
Browse
Maize bran
Hay
Total
2.5
2.5
5.0
7.5
10.0
45.0
39.0
30.0
21.0
12.0
47.5
46.5
45.0
43.5
42.0
(g/kg BW)
a
0
1
2
3
4
0
5.0
10.0
15.0
20.0
a
This level was excluded from further analyses.
50% of the amount of the browse offered. Level 0 had a small amount of MB, which
should not have been included. Daily amount of the supplements (maize bran browse)
in each level was calculated based on the animal's body weight (BW), and were 7.5,
15, 22.5 and 30 g/kg of the animals' BW for levels 1, 2, 3, and 4, respectively. Hay
offered was calculated such that total feed offered (supplements hay) would make up to
40 g/kg BW per day plus an allowance of 20% of hay as refusals. The goats were
randomly allocated to the treatments in an unbalanced design and were not blocked
for weight. It was assumed that differences in goat weight would not result in a
significant variation in the digestibility of a particular feed type. Actual amounts (g/kg
BW) of hay, maize bran and browse supplements provided are shown in Table 1.
Although the diets in Level 0 were offered through out the trial, the values for these
were excluded from analyses.
2.2. Feeding and data collection
After the acclimatisation period, the goats were fitted with faecal collection bags
and caged individually. During the 14-day experimental period, the goats were
provided with hay and the supplements (treatments). In each experimental period, there
was a preliminary period of seven days, followed by seven days of data collection, and
between each experimental period the animals were removed from the cages for 10 days.
Water and mineral block were accessible to the animals throughout the experimental
period. Each morning, at 8.00 h, the animals were provided with the test diets. The pods
and the MB were fed in a mixture, whereas the leaves and the MB were fed separately,
starting with MB followed by the leaves. Hay was provided immediately after
consumption of the test feeds. However, some supplements were not completely
consumed even after 6 h. Refused supplements were removed at 14.00 h, weighed, and
the animals provided with hay. Each morning, at 7.30 h, hay refusals from the previous
day for each animal were removed and weighed. About 10% of the refusals were
sub-sampled for dry matter (DM), organic matter (OM) and neutral detergent fibre
(NDF). Faeces were collected in the bags attached to the rear of the animal. Faecal
collection bags were emptied twice a day during the data collection period, weighed and
10% deep frozen for laboratory analyses.
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C.M. Shayo, P. UdeÂn / Animal Feed Science and Technology 82 (1999) 63±73
2.3. Laboratory analyses
DM, ash and CP contents of the feed samples and faeces were determined according to
the procedures of AOAC (1985), and NDF and acid detergent fibre (ADF) according to
Van Soest et al. (1991). The neutral detergent soluble fraction (NDS) was calculated on
OM basis and hemicellulose (Hem) was calculated as the difference between NDF and
ADF. Total phenolics were determined by the Folin±Ciocalteu method as described by
Waterman and Mole (1994). The extract was further diluted to 0.1 mg DM/ml.
Absorbance was read at 740 nm through a 1-cm cuvette.
2.4. Mathematical analyses
The true digestibilities of the NDS fraction and the metabolic contributions for
individual diets and all the diets combined were determined by regressing the digested
amount of NDS upon its percentage in the DM (Lucas, 1964).
The estimated true digestibilities were compared using a one-way analysis of variance
for differences between the species. For the species which showed significant differences,
the means were compared using Tukey's procedure at p < 0.05. To establish whether the
content of phenolic compounds had influenced NDS digestibility, the estimated true
digestibility of NDS for individual species was regressed upon the content of phenolic
compounds.
2.5. Results and discussion
The chemical compositions of the feeds used in the present study are shown in
Table 2. Except for F. albida and D. elata leaves, which had about 20% of CP, the
Table 2
Chemical composition of the feedstuffs offered to goatsa
Feedstuff
Ash
(% of DM)
CP
(% of OM)
NDF
NDS
ADF
Hem
Mulberry leaves
Acacia tortilis pods
Faidherbia albida pods
F. albida leaves
Dichrostachys cinerea pods
A. nilotica pods
Delonix elata leaves
A. tortilis leaves
Maize bran
Hay
12.8
5.9
4.4
5.5
6.3
5.8
7.5
6.4
2.7
5.7
13.2
14.1
11.8
19.2
10.4
10.7
21.6
12.8
10.1
2.8
23.5
31.8
36.2
35.4
40.4
22.2
52.9
45.6
33.4
73.5
63.7
62.3
59.4
59.1
53.3
72.0
39.6
48.0
63.9
15.4
20.4
26.6
28.8
25.3
32.5
17.2
31.1
43.1
8.7
49.4
3.1
5.2
7.4
10.1
7.9
4.6
21.8
2.5
24.7
24.1
Total soluble
phenolicsb
(740 nm)
32.8
53.8
79.3
46.8
106.8
294.8
108.7
118.2
nac
na
a
CP, crude protein; NDF, neutral detergent fibre; NDS, neutral detergent solubles; ADF, acid detergent fibre;
and Hem, hemicellulose.
b
Total soluble phenolic compounds presented as absorbance at 740 nm (units/100 mg DM/ml extract).
c
Not available.
C.M. Shayo, P. UdeÂn / Animal Feed Science and Technology 82 (1999) 63±73
67
other supplements had moderate values (10±14%). However, the CP content of the
browse species were higher than CP content in the basal diet in most grasses,
particularly during the dry season (Gupta and Pradhan, 1975). Despite the high CP
content, A. nilotica pods and A. tortilis and D. cinerea leaves were not well accepted by
the animals. In many cases, the animals could not completely consume the amounts
offered even after 6 h. Ground A. nilotica > pods formed a `gum-like' material in the
mouths of the goats which seemed to reduce intake. The other supplements were
completely consumed. Generally, ground pods took a longer time to finish as compared
with leaves.
Since the indigenous browse species have co-evolved with predator populations of
insects, bacteria, fungi and grazing animals they have developed defence mechanisms,
such as chemical defence, which can be deterrent, toxic or reduce intake and digestibility.
Tannins are known to reduce intake by various herbivores (Coley et al., 1985; Cooper and
Owen-Smith, 1985; Ahn et al., 1989). A. nilotica pods and A. tortilis and D. elata leaves
contained higher levels of phenolic compounds than the other browse species (except D.
cinerea pods) and this could have been one of the reasons for their low intakes. There
have been some studies also showing that intakes of A. nilotica pods by cattle, sheep and
goats were lower than in pods of other browse species containing lower levels of phenolic
compounds (Tanner et al., 1990; Shayo and UdeÂn, 1998). The low acceptance of A.
tortilis and D. elata leaves could also have been a result of mould developed on the leaves
during storage, as they were harvested two years before they were used in this study.
However, this was not the case in a study by Omar et al. (1998), who did not find any
reduced intake of mouldy mulberry leaves by goats, which could probably be an
indication that mould type may also be a factor.
The supplements had considerably higher NDS concentrations than the basal diet,
resulting in an increase in the NDS content of the diet with level of supplementation
(Table 3).
Relationships between the digested amount of NDS and its amount in the DM
consumed (Lucas test) for individual species and for all species combined are shown in
Table 4 and Fig. 1. However, A. nilotica pods, and A. tortilis and D. elata leaves were not
considered in this aspect due to their low and inconsistent intakes.
The slopes of the regression equations in the Lucas test, which are estimates of
the true digestibilities of NDS, were significantly (p < 0.05) different among the species.
Table 3
Mean NDS (% of DM) in the browse, maize bran and hay diets consumed by goats
Level
1
2
3
4
a
Feed
Total
hay
maize bran
browse
16.7
12.8
8.7
4.7
4.2
8.2
12.3
16.5
7.8
15.3
23.1
30.8
Mean of all the browse species.
a
28.7
36.3
44.2
52.0
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C.M. Shayo, P. UdeÂn / Animal Feed Science and Technology 82 (1999) 63±73
Table 4
Relationship between the digestible amount of the neutral detergent solubles (NDS) and increasing amount in
the dry matter of some tropical browse species by goats on maize bran and hay based diets
Species
Faidherbia albida pods
Acacia tortilis pods
Dichrostachys cinerea pods
F. albida leaves
Mulberry leaves
All species combined
a
Slopea
0.781a
0.968c
0.860b
1.042d
0.883b
0.919
Intercept
1.76
ÿ4.76
ÿ1.71
ÿ7.89
ÿ2.33
ÿ3.38
R2 (%)
95.8
98.6
98.2
98.9
98.0
96.9
Standard deviation
intercept
slope
residual
2.91
1.98
1.87
2.09
2.15
1.13
0.073
0.047
0.048
0.050
0.051
0.027
1.68
1.18
1.02
1.22
1.32
1.49
Values in the same column followed by different letters are significantly different (p < 0.05).
Feed fractions showing variable digestibilities are regarded to be non-ideal (Van
Soest, 1994). Although the NDS fraction of feeds is regarded as being almost completely available (Van Soest, 1994), the variability of the NDS fraction in the feeds
tested could have been due to the effect of tannins, since they can react with
carbohydrates, enzymes and proteins of the feeds to form indigestible complexes
(Hagerman et al., 1992; Reed and Soller, 1987; Robbins et al., 1987). According to Reed
et al. (1990), most complexes formed are not soluble in neutral detergent. As the
complexes are recovered in the NDF fraction of the faeces, the proportion of NDS in the
faeces is reduced, and thus the true digestibility value of the NDS is overestimated.
Therefore, the presence of tannins in the diet may result in an elevated slope in the
Lucas test. Reed et al. (1990) found that nitrogen in some tropical browse species was
not nutritionally uniform due to the presence of tannins. However, the degree of
precipitation of proteins depends on molecular weight and reactivity rather than
content of the tannins (Kumar, 1983; Makkar et al., 1990; Hagerman et al., 1992).
Probably, it is in this context that there was no significant (p > 0.05) relationship between
the content of phenolic compounds in the feeds and the estimated true digestibility of
the NDS fraction.
The findings in this study are in contrast with those of Van Soest (1967), Seoane
(1982), Laforest et al. (1986) and Christen et al. (1990), who reported that NDS in some
temperate legume and grass hays and silages were nutritionally uniform. However, in
another Lucas test with some temperate grass and legume hays Aerts et al. (1978)
did not find the cell contents to be nutritionally uniform. The authors obtained
true digestibility values much greater than 100% and suggested that this might have
resulted from increasing true digestibility of cell contents with increasing percentage
of cell contents, or from a decrease of metabolic matter with increasing percentage of
cell contents, or both.
In the present study, the metabolic amounts estimated from the Lucas test for the
individual species except F. albida leaves were not significantly (p > 0.05) different from
zero. The average metabolic fraction was lower (3.4 g/100 g of DM intake) than that
reported by Van Soest (1967), Aerts et al. (1978), Laforest et al. (1986), Seoane (1982)
C.M. Shayo, P. UdeÂn / Animal Feed Science and Technology 82 (1999) 63±73
69
Fig. 1. Test of nutritional uniformity of neutral detergent soluble fraction in Faidherbia albida pods (a), Acacia
tortilis pods (b), Dichrostachys cinerea pods (c), F. albida leaves (d), mulberry leaves (e) and all the species
combined (f). SDa, standard deviation of the constant; SDb, standard deviation of the regression slope; RSD,
residual standard deviation.
and Christen et al. (1990) of 12.9, 17.0-23.8, 6.6, 12.7 and 13.3 g/100 g of DM intake,
respectively. The reason for this difference is not clear.
3. Conclusions
This study has shown that NDS in some tropical browse is not a nutritionally
uniform entity, suggesting that digestibility of the NDS fraction in tropical browse species
70
C.M. Shayo, P. UdeÂn / Animal Feed Science and Technology 82 (1999) 63±73
Fig. 1 (Continued )
may not be predicted from its content. However, to confirm this, further work with
more species is necessary to determine if this is a general phenomenon with tropical
browse species.
Acknowledgements
The financial support of the Swedish Agency for Research Cooperation with
Developing Countries (SAREC) is gratefully acknowledged. Messrs Anthony Mbeho,
C.M. Shayo, P. UdeÂn / Animal Feed Science and Technology 82 (1999) 63±73
71
Fig. 1 (Continued )
Rehema Kasiga, Helina Nhonya and Hamisi Bakari of the Livestock Production Research
Institute, Mpwapwa, Tanzania, are thanked for their assistance in maintaining the animals
and for laboratory analyses.
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