In Sacco Dry Matter Degradability and In Vitro Gas Production Characteristics of Some Ghanaian Feeds
A K Tuah, D B Okai(1), E R Ørskov(1), D Kyle(1), Wshand(1), J F D
Greenhalgh(2), F Y Obese and P K Karikari
Department of Animal Science, UST, Kumasi, Ghana
(1) Rowett Research Institute, Aberdeen, Scotland, UK
(2) Gilfach, Rowen, Conwy, Gwynedd, Wales. U.K.
Abstract
The feeds comprised cocoa pod husk, coffee pulp, oil palm fruit bracts, untreated
and NaOH-treated maize cobs (Group 1) and whole stover, stem, tassels, leaves and husk of
two varieties of maize (Group 2). The nutritive index values of these feeds were also
calculated. The relationship between the in sacco dry matter degradability and in vitro
gas production values of the feeds in each group at 24, 48, 72 and 96h incubation periods
was determined using linear regression analysis. The nutritive index values of the feeds
in Group 1 ranged from 28 to 50 and for feeds in Group 2 from 25 to 43. The relationship
between the in sacco dry matter degradability and the in vitro gas production values at
the various incubation periods for the feeds in Groups 1 and 2 was high, positive, and
significant (r = 0.58 to 0.95).
Key words: In sacco dry matter degradation, in vitro gas production, Ghanaian feeds.
Introduction
In recent years there has been a considerable interest in the use of
agro-industrial by-products and crop residues for feeding small ruminants in Ghana (Tuah
1990). However, little is known about the nutritive value of such feedstuffs in Ghana and
other West African countries.
The nylon bag technique described by Ørskov et al (1980) for the determination of the
degradation of feedstuffs in the rumen at various incubation periods can be used to screen
feeds at the initial stages of assessing their nutritive values. Applying the equation of
McDonald (1981), p= a + b (1- e-ct), to describe the course of degradation of the feeds,
the constants, a, b, and c obtained can also be used to predict feed intake and growth
rate (Ørskov et al 1988). Blummel and Ørskov (1993) reported that the in vitro
gas production technique developed by Menke et al (1979) could also be used to determine
gas production at various incubation periods and these values could be used to describe
the course of fermentation of the feeds, by applying the equation of McDonald (1981).
These workers reported high positive correlation between the in vitro gas production and
the dry matter degradability values of the feeds at the various incubation periods
(Blummel et al 1993) (r = 0.95 to 0.97).
As part of a continuing study to characterise some Ghanaian agro-industrial by-products
and crop residues, the in vitro gas production and the nylon bag techniques were used in
the present study to assess the nutritive values of cocoa pod husk, coffee pulp, oil palm
fruit bracts, untreated and NaOH-treated maize cobs, and husks, stovers and botanical
fractions of stovers of two varieties of maize. In Ghana, cocoa and coffee are important
export crops and large quantities of their residues and by-products are produced. About
300,000 metric tons of dried cocoa beans are produced annually (Food and Agriculture
Organization of the UN 1990). Adomako (1975) estimated that for every 100kg of dried cocoa
beans produced, about 25kg of dried cocoa pod husk is produced and therefore about 75,000
metric tons of dried cocoa pod husk are produced annually. The production of palm oil in
Ghana is on the increase. In 1979, 21,000 t of palm oil were produced whilst in 1987
production had increased to about 72,500 t (Food and Agriculture Organization of the UN
1990). This increase is also associated with an increase in the production of crop
residues and by-products of oil palm. Maize is the major cereal crop grown in Ghana and
about 750,000 t of maize grains are produced annually (Food and Agriculture Organization
of the UN 1990). For every kg of maize grain 3 kg of fibrous by-products are produced
(Kossila 1984) indicating the production of about 2.25 million t of fibrous by-products
annually.
Because large quantities of these crop residues and by-products are present in the
country, there is need to study their nutritive values and also to determine the effects
of varieties of the various crops on the nutritive values of the residues.
Materials and methods
Feeds:
Stover (ie: stem and leaf after harvest) from two varieties of maize and its
botanical fractions, dried cocoa pod husk, coffee pulp, oil palm fruit bracts and
untreated and 5% NaOH-treated maize cobs were studied.
The stovers of the two maize varieties were obtained from the farm of the Department of
Animal Science, University of Science and Technology, Kumasi. One variety (variety 1) is
early-maturing (90 days) and is short. The other variety (Variety 2) is late-maturing (120
days) and is taller than the first variety. The local names for these varieties are
"Aburotia" and "Okomasa" respectively. They were grown on plots which
had been grazed by cattle for about 10 years. No fertilizers were applied during
cultivation of the maize. The dried cocoa pod husk (from mixed varieties of cocoa) was
supplied by the Cocoa Research Institute of Ghana, based in Tafo, and the coffee pulp
(variety, Robusta) was obtained from a coffee processing plant near Kumasi. The oil palm
fruit bracts (mixed varieties) were collected from a palm oil processing factory near
Atonsu, a suburb of Kumasi. The bracts were sun-dried. The maize cobs (mixed varieties)
were obtained from the Ghana Seed Company, Kumasi. The cobs were ground through a 3mm
sieve; some were treated with NaOH (50g NaOH/kg cobs dissolved in 2 kg water), the rest
were treated with water but not NaOH to serve as a control (untreated cobs). The two
fractions were dried in an oven at about 60oC for 48h.
Nylon-bag studies:
The feeds were ground through a 3-mm sieve and three replicate samples of each,
weighing about 3g, were put into nylon bags and incubated in the rumens of 3 fistulated
sheep (mean body weight 58 kg) to determine the degradability of the dry matter. The
incubation periods were 8, 16, 24, 48, 72, and 96h. The type of bag and incubation
procedures used were those described by Tuah et al (1986). The sheep were fed on a diet
(900g/head/daily at 0900 and 1600h) containing (per kg) 500g hay, 300g barley, 100g
molasses, 91g fishmeal, 5g dicalcium phosphate, 3g sodium chloride and 1g mineral and
vitamin premix. The premix contained (per kg) 185g Ca, 104g Mg, 2.25g Co, 44g Mn, 36.4g
Zn, 1.3g, I, 0.1g Se, 10,000, 000 i.u. retinol, 2,000,000 i.u., vitamin D3 and 40,000 i.u.
alpha-tocopherol. Washing losses were determined in triplicate by weighing about 3g of
each feed sample into nylon bags, soaking them in warm water (39o) for an hour and
subsequently washing the bags in a washing machine as was done for those incubated in the
rumen and finally drying the samples in an oven (60oC) for 48h. The course of degradation
of the feeds was described by using the equation of McDonald (1981), p -a + b (1 - e-ct).
The nutritive index value (NIV) of each feed was calculated using the formula of Ørskov
and Ryle (1990), NIV = a1 + 0.4b1 + 200c, where a1 is the actual washing loss and b1
= (a+b) - a1.
In-vitro Gas Production Studies:
The feeds were ground through a 1-mm sieve. Three replicate samples of each feed
(each weighing about 200mg) were then put into 100ml calibrated syringes together with a
rumen fluid plus buffer solution (about 30ml) and incubated in a water bath maintained at
39oC. A perspex lid with holes held the syringes upright in the water bath. The buffer
solutions used have previously been described by Menke et al. (1979). During any
incubation, there were also three blanks (rumen fluid + buffer solution) and three
replicates of a hay standard (about 200mg in each syringe). The rumen fluid was obtained
from the same sheep (fed on the same diet) used for the nylon bag studies and the fluid
was collected 1hr after the morning feeding. The fluid was strained through two layers of
cheese-cloth. The gas volume was recorded after 3,6,12, 24, 48, 72 and 96hr of incubation.
The initial volume of material in each syringe was also recorded before the commencement
of the incubation of the samples.
The following equation was used to estimate the volume of gas produced at any
incubation period:
GPt = [(SVt - SVo) - (BVt - BVo) x 0.200g]/ACW
where GPt = volume of gas produced at time "t". SVt = syringe reading for the
sample at time "t". SVo = syringe reading for the sample at the beginning of
incubation. BVo = mean of three replicates of blank readings at the beginning of the
incubation. BVt = mean of three replicates of blank readings at time t. ACW = actual
weight of the sample incubated on dry matter basis.
The equation of McDonald (1981) was used to describe the course of gas production.
Washing losses were not measured and were assumed to be zero.
Chemical Analysis:
The dry matter contents of all the feeds and the fat content of the oil palm fruit
bracts were determined according to the methods of the Association of Official Analytical
Chemists (AOAC 1980).
Statistical Analysis:
For the maize stovers and their botanical fractions, the values obtained at the
various incubation periods for both the in sacco dry matter degradability (DMD) and the in
vitro gas production were subjected to statistical analysis using Genstat 5 (Lawes
Agricultural Trust 1990). The differences between means were compared using Tukey's
Honestly significant test (Steel and Torrie 1980). The correlations between the in sacco
DMD and in vitro gas production values at 24, 48, 72 and 96hr for the maize stovers and
their botanical fractions and husks (Group 2) and cocoa pod husk, coffee pulp, oil palm
fruit bracts, untreated and NaOH-treated cobs (Group 1) were determined using Genstat 5
(Lawes Agricultural Trust 1990).
Results and discussion
Cocoa pod husk, coffee pulp, oil palm fruit bracts, untreated maize cobs and
NaOH-treated maize cobs (group 1)
* - Washing loss
| Table 2: Equation terms for group 1
feeds incubated in sacco, including residual standar deviations (rsd) and nutritive index
values (n/v) |
 |
|
a |
b |
c |
Lag Time (hr) |
RSD |
NIV |
|
| Cocoa pod husk |
20.5 |
38.0 |
0.02 |
4.0 |
1.7 |
42.9 |
| Maize cob (NaOH treated) |
16.3 |
72.2 |
0.02 |
5.9 |
1.8 |
50.1 |
| Maize cob (untreated) |
-6.0 |
63.9 |
0.0 |
8.0 |
1.8 |
30.6 |
| Coffee pulp |
12.7 |
29.4 |
0.0 |
3.6 |
0.6 |
34.7 |
| Oil palm fruit bracts |
11.7 |
20.3 |
0.0 |
6.0 |
1.0 |
27.6 |
|
The washing losses and the in sacco dry matter degradability and in vitro gas
production values of the feeds are shown in Tables 1, 2, 3 and 4, respectively. While
cocoa pod husk had the highest degradability values at 8 and 16hr incubation periods, the
treated maize cobs had the highest degradability values at the 24, 48, 72 and 96hr
incubation periods. Cocoa pod husk had the highest in vitro gas production values at the
3, 6 and 12hr incubation periods; after those incubation periods treated maize cobs had
the highest in vitro gas production values. Untreated maize cobs also had higher in vitro
gas production values than cocoa pod husk at the 48, 72 and 96hr incubation periods. Cocoa
pod husk is degraded to a greater extent than all the other feeds in the early hours of
incubation perhaps because it has greater amounts of readily degradable cell contents than
the others. Tuah and Ørskov (1989) reported that cocoa pod husk had greater amounts of
cell contents than maize cobs (406 and 60 g/kg DM, respectively).
Although the untreated maize cob may be degraded to the same or greater extent as cocoa
pod husk after 24hr incubation, if it is given to animals the in vivo apparent
digestibility coefficient of dry matter may be low, unless the particles remain in the
rumen for a period longer than 24hr. Coffee pulp had degradability values greater than
those of untreated maize cobs at the 8, 16, 24 and 48hr incubation periods. However, the
in vitro gas production values exceeded those of untreated maize cob only at 3 and 6hr
incubation periods. Oil palm fruit bracts also had higher degradability values than
untreated maize cobs at 8, 16, and 24hr incubation periods. The in vitro gas production
values of oil palm fruit bracts were, however, greater than those of untreated maize cob
at only 3 and 6hr incubation periods. It is likely that the oil palm fruit bracts and
coffee pulp may contain some anti-microbial factors which could affect the in vitro gas
production values but did not affect the degradability values. There was a build-up of
these factors with time in the syringes while in the case of the in sacco dry matter
degradability technique, these factors were washed out from the bags into the rumen
content and their effects would not be felt. The suspected anti-microbial factors are
tannins in the coffee pulp and high lipid content in the oil palm fruit bracts (99g oil/kg
DM.
| Table 4: Equation terms for gas
production from group 1 feeds |
|
| Feeds |
a |
b |
c |
Lag time (h) |
RSD |
|
| Cocoa pod husk |
2.5 |
29.6 |
0.0 |
0.0 |
0.21 |
| Maize cob (NaOH treated) |
-7.4 |
66.5 |
0.0 |
2.5 |
1.62 |
| Maize cob (untreated) |
-5.7 |
54.0 |
0.0 |
3.6 |
1.46 |
| Coffee pulp |
-1.2 |
21.7 |
0.0 |
0.9 |
0.23 |
| Oil palm fruit bracts |
1.1 |
13.7 |
0.0 |
0.0 |
0.71 |
|
| Table 5: Relationship for group 1 feeds
between gas production (x ml/200 mg dm) and dry matter degradability in sacco (y, %) for
various incubation periods |
|
| Time (hr) |
Equation |
SE |
r |
Significance |
|
| 24 |
y = 20.7+0.4x |
0.1 |
0.58 |
* |
| 48 |
y = 21.5+0.7x |
0.15 |
0.80 |
** |
| 72 |
y = 21.0+0.8x |
0.1 |
0.89 |
** |
| 96 |
y = 20.8+0.9x |
0.1 |
0.91 |
** |
|
* Significant at P<0.05
** Significant at P<0.01
The nutritive index values for these feeds, except for treated maize cobs, were
generally low and comparable to the values reported for straws by rskov and Ryle (1990).
The correlation between the in sacco dry matter degradability and in vitro gas production
values was high, positive and statistically significant (P<0.05 and P<0.01; Table
5). It is therefore suggested that with these feeds, except coffee pulp and oil palm fruit
bracts, either of the two methods could be used to assess their degradation
characteristics. These feeds were not pulverized with grinding and this probably accounted
for the good relationship existing between in sacco dry matter degradability and in vitro
gas production values.
* - Washing loss.
SE Standard error of difference.
ab Means in the same column bearing different superscripts are significantly (P<0.05)
different.
Maize stover, maize stover botanical fractions and husks (group 2):
The washing losses and the in sacco dry matter degradability and in vitro gas
production values of the whole stover, botanical fractions of the stovers and husk of the
two varieties of maize are shown in Tables 6, 7, 8 and 9.
| Table 7: Equation terms for group 2
feeds incubated in sacco, including residual standard deviations (RSD) and nutritive index
values (NIV) |
|
Maize - Part
Variety |
a |
b |
c |
Lag time (h) |
RSD |
NIV |
|
| 1 Whole stover |
5.4 |
48.8 |
0.0330 |
2.9 |
0.91 |
34.4 |
| 1 Stem |
11.1 |
35.6 |
0.0198 |
5.2 |
1.48 |
31.3 |
| 1 Leaves |
-4.9 |
69.5 |
0.0381 |
7.0 |
1.68 |
40.3 |
| 1 Husk |
-0.2 |
81.8 |
0.0206 |
3.8 |
2.31 |
40.2 |
| 2 Whole stover |
0.8 |
51.1 |
0.0367 |
4.1 |
1.85 |
32.9 |
| 2 Stem |
5.2 |
34.2 |
0.0219 |
3.5 |
0.93 |
24.8 |
| 2 Leaves |
-3.8 |
70.0 |
0.0288 |
7.4 |
2.27 |
38.0 |
| 2 Husk |
-5.2 |
92.3 |
0.0243 |
5.4 |
1.71 |
43.3 |
| 1 Tassels |
|
|
|
|
|
|
| 2 Tassels |
|
|
|
|
|
|
|
There was no significant difference (P>0.05) between the whole stover of the two
varieties at any of the incubation periods, for both the in sacco dry matter degradation
and the in vitro gas production determinations. The values of the washing losses were also
not significantly different.
The degradability values of the stem of variety I (Aburotia) were generally higher than
values for variety 2 (Okomasa) at all the incubation periods but the values were only
significantly different at the 24hr incubation period. The in vitro gas production values
were also significantly greater for the stem of variety 1 than the stem of variety 2 at
the 24, 48, 72 and 96hr incubation periods.
As mentioned earlier, Variety 1 is short and the stem is relatively big and it is
possible that it has more pith than the stem of variety 2 which is tall and slender. The
pith is more degradable than the rind. It is also possible that the stem of variety 2 was
more lignified than the stem of variety 1 for support to prevent lodging and this could
also adversely affect its degradation. The leaves of variety 1 also generally had higher
degradability values than the leaves of variety 2. The differences were however, not
significant at any of the incubation periods. The washing losses were also not
significantly different. With respect to the in vitro gas production, the leaves of
variety 1 had generally but not significantly higher values than the leaves of variety 2
except during the 3, 6 and 12h incubation periods. It is surprising that the in sacco
degradability and in vitro gas production values were not significantly different at the
different incubation periods for the whole stover of the two varieties since generally
variety 1 had higher values for stem and leaves than variety 2.
a-e Means in the same column bearing different superscripts are significantly
(P<0.05) different.
The in vitro gas production values for the tassels of the two varieties were not
significantly different at any of the incubation periods. The degradability values also
for the tassels of the two varieties were not significantly different at the 24 and 48hr
incubation periods for which there were enough samples for the determinations.
There was no significant varietal effect on the in sacco dry matter degradability and
the in vitro gas production values for the husks. The husks generally had similar or
higher values for the in sacco dry matter degradability and in vitro gas production
measurements than the leaves, especially at the 24, 48, 72 and 96hr incubation periods. If
the husk can be retained in the rumen for more than 24hr, it may have higher in vivo dry
matter degradability than the leaves. The leaf fraction also generally had higher
degradability and in vitro gas production values than the stem or whole stover in the two
varieties. The tassels had the lowest degradability and in vitro gas production values.
This fraction, however, forms only a small proportion of the maize stover.
| Table 9: Equation terms for gas
production from group 2 feeds |
|
Maize -
Part Variety |
a |
b |
c |
Lag time (hr) |
RSD |
|
| 1 Whole stover |
-2.9 |
48.0 |
0.0246 |
2.5 |
1.16 |
| 1 Stem |
-0.6 |
39.8 |
0.0253 |
0.6 |
0.54 |
| 1 Leaves |
-6.5 |
58.8 |
0.0363 |
3.2 |
1.77 |
| 1 Husk |
-8.8 |
72.2 |
0.0322 |
4.1 |
2.39 |
| 1 Tassels |
|
57.5 |
0.0079 |
2.0 |
0.53 |
| 2 Whole stover |
-3.7 |
44.6 |
0.0280 |
3.2 |
1.24 |
| 2 Stem |
-1.4 |
39.2 |
0.0179 |
2.1 |
0.76 |
| 2 Leaves |
-5.5 |
55.4 |
0.0333 |
3.1 |
1.76 |
| 2 Husk |
-7.7 |
72.0 |
0.0311 |
3.7 |
2.04 |
| 2 Tassels |
-1.7 |
52.5 |
0.0089 |
3.7 |
0.67 |
|
Generally, the nutritive index values, except for stem of variety 2, were similar to
the values reported for straws by Ørskov and Ryle (1990). The values for the husks and
leaves were higher than the value of 35 which these authors suggested as the minimum value
to satisfy maintenance energy requirements.
The correlation between the in sacco dry matter degradability and in vitro gas
production values at 24, 48, 72 and 96hr incubation periods was highly significant
(P<0.01; Table 10) and positive, indicating that either of the two methods could be
used to study the degradation characteristics of the stover and its botanical fractions.
Grinding the feeds through a 3 mm seive did not reduce them to the consistency which may
lead to considerable loss of particulate matter through the pores of the rumen bags.
| Table 10: The relationship for group 2
feeds between gas production (x ml/200 mg dm) and dry matter degradability in sacco (y, %)
for various incubation periods |
|
| Time (hr) |
Equation |
SE |
r |
Significance |
|
| 24 |
Y = 9.9+0.8x |
0.10 |
0.86 |
** |
| 48 |
Y = 13.5+0.9x |
0.08 |
0.90 |
** |
| 72 |
Y = 6.2+1.0x |
0.11 |
0.95 |
** |
| 96 |
Y = 2.5+1.3x |
0.10 |
0.9 |
** |
|
Conclusion
The studies indicated that oil palm fruit bracts and coffee pulp are poor quality
feeds while cocoa pod husk and untreated corn cob are only slightly better. The stovers of
the two varieties of maize have similar nutritive values. With these feeds, either the in
sacco dry matter degradability or the in vitro gas production method could be used to
assess nutritive value, since there was a very good positive relationship between the two
methods.
Acknowledgement
The authors are grateful to the European Community for funding the research. Mrs M
Ankoma and Ms Cecilia Araba Turkson are thanked for typing the script.
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