| Livestock Research for Rural Development 33 (2) 2021 | LRRD Search | LRRD Misssion | Guide for preparation of papers | LRRD Newsletter | Citation of this paper |
This study was conducted in Gelana Rangelands, Southern Ethiopia to evaluate potential yield, chemical composition and in-vitro gas production potential of selected indigenous multipurpose browse trees. Eight browse species were selected based on their relative palatability, preference by ruminant, multiple function and availability in the dry season. The leaves of selected browse species were collected during wet and dry seasons for the determination of chemical composition and in vitro gas production test. A significant difference (P<0.05) in leaf biomass yield was observed between browse species where the value ranged from 0.77 to 3.3(kg/tree). The average Dry Matter (DM) yield was higher (P< 0.05) in the wet than the dry season. Crude protein (CP) content was higher (P< 0.05) in the wet season except for R. albersii which had a higher value in the dry season. Both the value of Neutral Detergent Fiber (NDF) and Acid Detergent Fiber (ADF) were highest (P< 0.05) in F. thonningii while the lowest values for both NDF and ADF were recorded in R. albersii. The condensed tannin (CT) value ranged from 0.2 to 11.13% (DM) in V. amygalina and D. angustifolia, respectively in the wet season while the CT values of browse trees ranged from 0.45% to 9.95% DM in the same species in the dry season, respectively. The total gas production at 24 hr incubation ranged from 13-50 ml/200 mg DM, gas production at 48 hr incubation 24-55.5 ml/200 mg DM in the wet season, and 21-51to 30-65 ml/200 mg DM in the dry season, respectively. Organic Matter Digestibility (OMD) ranged from 56.72-90.23 %, Metabolizable Energy (ME) 4.25-9.15 MJ/kg DM, and Short Chain Fatty Acid( SCFA) 0.25-1.13 mmol/L in wet season while 54.78-95.63 %, 5.13-9.27 MJ/kg DM and 0.44-1.16 mmol/L in dry season, respectively. R. albersii, V. amygalina and C. africana leaves were best in terms of gas volume, OMD, ME and SCFA production potential characteristics. Therefore, the three tree species had the best nutritive value and could be considered as potential sources of animal feed supplement during the dry season when regular feed resources are limited in quality and quantity.
Keywords: Celtis africana, Dodonea angustifolia, Ficus thonningii, Richiea albersii, Vernonia amygdalina
Browse trees and shrubs are the main feed resource for domestic livestock and wild animals in the arid and semi-arid areas of Ethiopia. Browse trees and shrubs are adapted to a low moisture environment, thus offer a reliable source of feed in the form of leaves and fruits (Dalle et al, 2006). During the dry season, when plant growth is highly suppressed, a shortage of forage availability reduces the growth of grazing animals. This also affects nutrient requirements and bioavailability of minerals in grazing animals. Furthermore, in the dry season, most ruminants reared on grass alone have problems in meeting their maintenance requirements and consequently lose weight gained during the wet season. The most significant contribution of browse tree species as animal feed is that it serves as a source of crude protein as well as its ability to be green for a longer time during the dry season (Devendra, 1993).
To alleviate the animal feed supply problem, looking for potential feed resources, particularly those which survive during the dry season, deserves due attention. In this regard, the use of browse tree species has great potential (Getachew, 2005). Some studies (Getachew, 2005; Dalle et al, 2006; Kassahun et al 2016; Abebe et al 2012) are conducted on the use and nutritive value of indigenous multipurpose browse trees as a source of feed for ruminant in different areas. However, well-documented information on potential yield, nutritive value and in-vitro gas production of indigenous multipurpose browse trees are not available in the Gelana Rangelands. This needs assessment of the type, amount, quality, seasonal performance and overall utilization of existing local browse trees in a given locality. Therefore, this study was initiated with the objectives of evaluating seasonal variations in biomass yield and nutritional qualities of selected browse species.
This study was conducted in Gelana rangelands, southern Ethiopia, located between 5o 44' 10" to 6o 40' 10" N latitude and 37o 44' 10" to 38o 19' 40" E longitude. The elevation of the area ranges from 1300 to 2100 meters above sea level. The climate condition of the study area is characterized by moderately moist and wet to hot temperature with bimodal rain and the temperature ranges from 22oC to 24oC. Two agro-ecological zones, namely Midland ( Badadaree) and lowland (Gammoojjii) are typical characteristics of the area. Generally, the soil types of the area are classified as (25%) black, (5%) red and (70%) sandy.
Group discussion with key informant and elders were held to select, identify and prioritize the indigenous multipurpose browse tree species. Accordingly, the pastoralists listed out and prioritized browse tree species by vernacular names. Scientific names were consulted from Hedberg and Edwards (1989). The common indigenous browse species identified in the area is presented in Table 1. A total of 17 browse tree species were selected, listed and prioritized. Out of which eight browse species were selected based on their availability, relative palatability and preference by ruminant, multiple function and ability to maintain greenness in the dry season. These browse tree species were reported being used as feed sources by cattle, goats and sheep. Browse species were consumed at one time or another during the year, depending upon foliage availability and preference by animal species.
Leaves sample of the 8 selected browse trees were collected during wet (September to November, 2017) and dry (January to February, 2018) seasons. The samples were air-dried in a well-ventilated room until transported to Dilla University Soil Laboratory and then oven-dried at 65oC for 24 hours. The samples were separately ground in a Willey mill to pass through 1 mm sieve. The samples were then put in plastic bags and sealed for further analysis.
Chemical analysis DM, OM, Ash, and N (Kjeldahl-N) content of samples were analyzed based on the analysis method of the AOAC (1990). Crude protein (CP) was calculated as N x 6.25. Neutral detergent fiber (NDF), acid detergent fiber (ADF) and acid detergent lignin (ADL) were analyzed by using the procedure described by (Van Soest et al 1991). Condensed tannin was analyzed according to (Makkar, 2003).
|
Table 1. Major browse tree species identified |
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|
Local Name |
Family |
Scientific Name |
Ecology |
|
|
LL |
ML |
|||
|
Mottoqomaa |
Cannabaceae |
Celtis africana |
A |
A |
|
Qalqalcha |
Capparidaceae |
Richiea albersii |
NA |
A |
|
Biiqqaa |
Sapindaceae |
Pappea capensi |
NA |
A |
|
Rukeensa |
Combretaceae |
Combretum molle |
A |
A |
|
Dhitacha |
Sapindaceae |
Dodonea angustifolia |
A |
A |
|
Ebicha |
Asteraceae |
Vernonia amygdalina |
A |
NA |
|
Dhandhallee |
Combretaceae |
Combretum collinum |
NA |
A |
|
Dambii |
Moraceae |
Ficus thonningii |
A |
NA |
|
Halloo |
Fabaceae |
Acacia bussei |
A |
A |
|
Gambeelloo |
Rubiaceae |
Gardenia ternifolia |
A |
A |
|
Dhaadhatuu |
Fabaceae |
Millettia ferruginea |
A |
NA |
|
Daboobessa |
Anacardiaceae |
Rhus valgarisnatalensis |
A |
A |
|
Waaccuu |
Fabaceae |
Acacia seyal |
A |
A |
|
Woddeesa |
Boraginaceae |
Cordial Africana |
A |
NA |
|
Hagalaa |
Celastraceae |
Mytumus addat |
+ |
+ |
|
Qilxaa |
Moraceae |
Ficus vasta |
+ |
NA |
|
Baddannee |
Balanitacea |
Balanites aegyptica |
NA |
+ |
|
A= Available; NA = not available; ML = midland; LL= lowland |
||||
The potential yield of browses is the foliage available for defoliation. Using measuring tape, the circumference measurements of trees for each selected MPT species were taken and the diameter was calculated as described by Petmak (1983) as follows:
D = 0.636C,
Where;
D=diameter
C= circumference.
The yield potential of the MPT species was estimated using the following equation as described by (Petmak, 1983).
Log W= 2.24Log DT-1.50
Where
W= leaf yield in kilograms of dry weight and
DT= trunk diameter (cm) at 130cm height for trees.
Rumen fluid was obtained from the rumen of three sheep from Dilla University farms that were housed in individual cages and fed on sample hay daily with free access to water and mineral licks. A sample of rumen content was collected using rumen tube before the morning meal in thermos flasks, taken immediately to the laboratory, strained through several layers of cheesecloth, and kept at 39ºC under a CO2 atmosphere.
About 200 mg of dry sample (milled through a 1.0 mm sieve) was incubated in vitro with rumen fluid in a calibrated glass syringe of 100 ml in triplicate. Vaseline was applied to the pistons to ease movement and prevent the escape of gas. The syringes were pre-warmed at 39°C before the addition of 30 ml of buffer mixture and rumen liquor into each syringe. The syringes were shaken gently 30 min after the start of incubation and every hour for the first 10hr of incubation. Rhodes grass was used as control and the same procedure was applied as the feed samples. Blanks with buffered rumen fluid without feed samples were also included in triplicate. All the syringes were incubated in a water bath maintained at 39°C. Gas production was recorded after 3, 6, 12, 24 and 48 hours of incubation. The gas production characteristics were estimated by fitting the mean gas volumes to the exponential equation of Ørskov and Mc Donald (1979): G = a + b (1-e-ct), where G is the gas production (ml/200mg OM) at time t, a is the intercept of the gas production curve, b is the extent of gas production, a + b is the potential gas production (ml/200 mg OM), and c is the rate constant of gas production (Blümmel and Ørskov,1993).
1. Organic matter digestibility (OMD) was calculated from the equation:
OMD (%) = OMD = 14.88 + 0.889GV+ 0.45 CP + 0.651ash (Menke, 1979).
Where:
OMD= organic matter digestibility at 24 hours.
CP=Crude protein content of feed samples
GV= Gas volume
2. Metabolizable energy (ME) was calculated from the equation:
ME (KJ/g DM) =2.20+0.136GP+0.0057CP (Menke, 1979).
Where:
GP=Gas production over 24rs of incubation
CP=Crude protein content of feed samples.
Short-chain fatty acids (SCFA) were estimated as:
3. SCFA (mmol/L) = 0.0239GV−0.0601(Getachew,2000)
Where: GV = gas volume 24rs of incubation
Data were subjected to the analysis of variance procedure of the statistical analysis system (SAS, 2008). Means were separated using Duncan News Multiple Range Test. The level of significance was determined at (P<0.05). Results were presented using descriptive statistics such as mean, percentage, standard deviation.
The estimated biomass yield of selected browse tree species is presented in Table 2. The result indicated that there was a significant difference (P<0.05) in biomass yield among the browse species compared. The biomass yield of leaves that can be defoliated for animal feeding varied (P < 0.05) among the selected MPT (Table 2). The highest yield recorded in F. thonningii followed by P. capensi and lowest in D. angustifolia. The variation among tree species in biomass yield might be associated with differences in the growth characteristics of the browse trees (Anele, 2009).
|
Table 2. Estimated leaf biomass yields (kg DM/tree) of the eight selected indigenous multipurpose browse tree species |
||||
|
Browse species |
TC(cm) |
TD (cm) |
PY (kg/tree) |
|
|
C. africana |
49.33 |
31.38 |
1.61 ± 0.87bc |
|
|
R. albersii |
52.33 |
33.28 |
1.86 ± 0.40bc |
|
|
P. capensi |
75.00 |
47.70 |
2.25 ± 0.14b |
|
|
C. molle |
40.33 |
25.65 |
1.64 ± 0.24bc |
|
|
D. angustifolia |
16.33 |
10.39 |
0.77 ± 0.90d |
|
|
V. amygdalina |
28.00 |
17.81 |
1.30 ±0 .04cd |
|
|
C. collinum |
49.00 |
31.17 |
1.74 ±0.59bc |
|
|
F. thonningii |
220.67 |
140.34 |
3.30 ± 0.17a |
|
|
abcd means in a column with different superscripts are significantly different (P < 0.05) TC= Trunk circumference, TD= Trunk Diameter, PY= Potential yield |
||||
The chemical composition of leaves of selected browse tree species is presented in (Table 3). Significant variations (P<0.05) were observed among species in chemical composition (DM, CP, NDF, ADF, ADL, ash) and condensed tannin contents both during the wet and dry seasons. Variability in species of the plants, physiological stage and season of harvesting, environmental factors and the botanical fraction of plants could be some of the factors affecting the chemical composition of the browse species (Debella and Tolera, 2013).
The average dry matter content for the current study for the wet season was 32.4%, This variation in DM content could be attributed to the season, at which plants were collected, differences in species of plants and stage of harvest. The higher DM contents of the MPT observed during the dry season may be a result of reduced photosynthetic activity due to the lower moisture levels experienced during the dry season relative to wet seasons. The high DM observed could also be attributed to the well-matured leaves which have lost some moisture during the dry season (Anele et al 2009; Debella and Tolera, 2013).
The Crude protein content was in the order of R. albersii >V. amygdalina > F. thonningii >D. angustifolia > C. africana > P. capensi > C. collinum > C. molle. Except for R. albersii (28.75%), the CP content of the browse tree species, were lower in the dry season comparing with the wet season. The CP content of the browse trees studied was generally higher. The rumen fermentation is affected if the CP level in the diet is less than 10% (Alam and Djajanigara, 1994). However, CP level in the current browse trees was higher than this threshold. Differences in CP contents between leaves of different browse trees might be due to differences in protein accumulation characteristics of the species during growth. The high CP content makes the browse tree species suitable as protein supplements to poor quality pasture and fibrous crop residues for goats, sheep and cattle which are dominant livestock species in the study area. The value observed for CP contents of these browse trees in the dry season was higher than the minimum requirement (7- 8%) necessary to provide the minimum ammonia levels required by rumen micro-organisms to support optimum rumen activity (Alam and Djajanigara 1994; Norton 2003).
The NDF content varied from 41.56% in R. albersii to 67.06% inP. capensi, while the ADF content ranged from 21.23% in R. albersii to 52.73% in F. thonningii. The lowest ADL content (11.69%) was recorded in R. albersii and the highest (28.32%) in F. thonningii. The NDF contents of browse trees in the current study (Table 3) are categorized as high quality for D. angustifolia (43.96%) and R. albersii (41.1%) and other four browse tree species C. molle, C. africana, V. amygdalina and C. collinum could be categorized as medium quality (McDonald 2002). High-quality feeds are not imposing limitations on feed intake and animal production. The ADF content ranged from 18.88% in R. albersii to 49.24% in F. thonningii. Those browse tree species with higher ADF content may have lower digestibility since the digestibility of feed and ADF content is negatively correlated (McDonald 2002).
|
Table 3. Chemical compositions of the leaves of some browse tree species during the wet and dry seasons |
||||||||
|
Season |
Species |
DM |
CP |
Ash |
NDF |
ADF |
ADL |
CT |
|
Wet |
C. africana |
33.6 ± 0.6a |
21.2 ± 0.8abcd |
21.8 ± 1.52a |
56.9 ± 19.6ab |
29.2 ±12.9cd |
14.2 ± 9.23bcd |
0.53 ± 0.26c |
|
R. albersii |
34.2 ± 4.8a |
26.2 ± 1.48a |
21.1 ± 4.76a |
41.1 ± 4.15b |
18.9 ± 2.18d |
8.5 ± 2.53d |
0.77 ±0.1c |
|
|
P. capensi |
39.5 ± 0.46a |
20.5 ± 2.47bcd |
10.1 ± 0.45c |
65.2 ± 3.07a |
43.6 ± 1.22ab |
21.6 ± 2.64ab |
5.2 ± 2.65b |
|
|
C. molle |
37.9 ± 2.26a |
18.0 ± 1.18d |
9.35 ± 1.2c |
50.2 ± 0.52ab |
28.5 ± 0.59cd |
11.5 ± 0.37cd |
2.5 ± 0.27bc |
|
|
D. angustifolia |
35.0 ± 0.2a |
22.5 ± 3.13abcd |
9.03 ± 1.33c |
43.9 ± 4.91b |
27.5 ± 2.44cd |
18.3 ± 1.83abc |
11.1 ± 0.46a |
|
|
V. amygdalina |
18.7 ± 2.26c |
25.4 ± 1.09ab |
15.51 ± 3.13b |
59.1 ± 0.81ab |
38.6 ± 0.63abc |
21.9 ± 0.9ab |
0.2 ± 0.01c |
|
|
C. collinum |
35.3 ± 3.38a |
19.8 ± 1.13cd |
9.6 ± 2.14c |
59.4 ± 3.14ab |
33.9 ± 1.31bc |
14.7 ± 1.47bcd |
11.1 ± 2.26a |
|
|
F. thonningii |
25.1 ± 1.22b |
24.5 ± 3.71abc |
20.7 ± 2.11a |
67.8 ± 1.16a |
49.2 ± 0.01a |
26.6 ± 0.5a |
0.52 ± 0.1c |
|
|
Dry |
C. africana |
43.3 ± 0.48b |
19.33±1.68bc |
21.92±2.18ab |
60.9±2.25b |
34.07±1.24e |
19.77±0.18d |
0.76±0.77b |
|
R. albersii |
45.5 ± 8b |
28.75±0.37a |
19.86±1.35b |
41.56±2.16e |
21.23±0.09f |
11.69±0.74e |
1.27±0b |
|
|
P. capensi |
98.12±0.25a |
10.05±2.3e |
13.92±0.93c |
67.06±2.24a |
47.67±1.55b |
23.08±0.89c |
5.35±1.26ab |
|
|
C. molle |
97.79±1.46a |
13.59±2.68de |
10.93±0.42de |
56.51±0.04c |
40.28±0.58d |
25.29±0.57b |
2.15±0.08b |
|
|
D. angustifolia |
45.42±1.06b |
21.35±0.27bc |
8.85±1.31e |
48.63±0.25d |
35.67±0.06e |
23.55±0.99c |
9.95±3.37a |
|
|
V. amygdalina |
31.93±1.15c |
23.4±2.06b |
13.43±0.96cd |
41.69±0.09e |
22.6±0.41f |
12.56±0.42e |
0.45±0.31b |
|
|
C. collinum |
98.34±0.55a |
17.11±2.47cd |
10.82±0.57de |
63.06±2.09b |
43.65±0.28c |
12.72±0.2e |
5.17±1.9ab |
|
|
F. thonningii |
34.99±1.53c |
22.54±1.48b |
23.92±0.65a |
53.71±1.5c |
52.73±0.29a |
28.32±0.36a |
5.64±4.21ab |
|
|
|
Main effects |
|||||||
|
Season |
**** |
*** |
*** |
*** |
* |
* |
*** |
|
|
Species |
**** |
*** |
*** |
*** |
*** |
*** |
*** |
|
|
Species x season |
**** |
* |
NS |
* |
** |
** |
* |
|
|
Column means with different superscripts are significantly different (P<0.05); CP is crude protein; NDF is neutral detergent fiber; ADF is acid detergent fiber; ADL is acid detergent lignin; *(P<0.05); ** (P<0.01); *** (P<0.001); NS (The effect is not significant) |
||||||||
The condensed tannins content in this study varied (P<0.05) , from 0.2% DM in V. amygdalina to 11.13% DM in D. angustifolia. Feeding tannin containing browse can decrease ruminal protein degradation, promote microbial crude protein (CP) synthesis and prevent excessive ruminal gas formation which can lead to bloat. However, in ruminants, dietary condensed tannins of 2 - 3% DM have been shown to have beneficial effects because they reduce the protein degradation in the rumen by the formation of a protein-tannin complex and increasing absorption of amino acids in the small intestine (Aganga et al 1997). Moderate concentration of CT (2-4.5% DM) can exert beneficial effects on protein metabolism in ruminants, high dietary CT concentrations (>5.5% DM) can depress voluntary feed intake, digestive efficiency and animal productivity. Based on this, except for D. angustifolia (11.13% DM) and C. collinum (11.06% DM) which have high condensed tannin and can depress voluntary feed intake, digestive efficiency and animal productivity, all other browse tree species in the current study area have a beneficial effect to reduce the protein degradation in the rumen and can exert beneficial effects on protein metabolism in ruminants. However, effects are not the same for all CT as they depend upon its chemical structure (Aganga et al 1997; Makkar 2002).
The range of DM % was higher (P <0.05) in the dry season (31.93–98.34%) than in the wet season (18.68–39.53%). In both seasons, V. amygdalina had the lowest DM content. The high range of DM% could be taken as good indicator for nutrients supplement to feed intake of browse components. The higher DM may indicate species free of fiber tissues (Gaiballa and Lee 2012). All species had the highest CP value during the wet season and the lowest during the dry season. R. albersii (26.42%) had the highest (P< 0.05) CP concentration in both wet and dry season while C. Molle and P. capensi had the lowest concentration 18.04% and 10.05% in wet and dry seasons, respectively. The average CP % concentration was higher (P< 0.05) in the wet season (22.27%) than in the dry season (19.51%). All browse tree species of the current study except for R. albersii (28.75%), had higher CP concentrations in the wet season than in the dry season. A higher CP content during the wet season compared with the dry season occur between plant species and between seasons with higher values reported for seasons with higher moisture levels. The CP content ranged from 18.04-26.24% to 10.05-28.75% in wet and dry season respectively, which is greater than the minimum required level for best microbial activity in the rumen 7- 8% (Norton 2003). However, CP level in these browse trees was higher than this level in both seasons. The higher CP content of the multipurpose trees (MPT) in the wet season was due to the continuous flush (regrowth) of leaves during this season. The lower CP contents during the dry season may be largely due to moisture stress experienced by the trees during this period and buildup of lignocellulosic fiber structures of the plants, diluting the nitrogen (Anele et al 2009).
The ADF and ADL content of the browse species varied (P<0.05) between seasons.
In the dry season, the plant species had the highest fibre fractions (NDF, ADF and ADL) while in the wet season browse species attained the lowest values. The NDF level of forage above 65% can limit feed intake and roughages with above 40% are low quality These variations are a useful offer of the browse species since the voluntary intake and digestibility are controlled by fiber concentration particularly NDF and ADL (Meissner et al 1991; Kellems and Church 1998).
The browse tree species in the wet season had the highest CT level. The D. angustifolia (11.13% DM) and C. collinum (11.06% DM) contained the highest level of tannins at the wet season, which decreased to 9.95% DM and 5.17% DM respectively at the dry season. In dry season the values ranged from 0.45% DM in V. amygdalina to 11.06% DM in D. angustifolia. Several factors are known to have a significant effect on condensed tannin analysis. Such factors include initial harvesting, drying and extraction method of the forage material. Even within species condensed tannin can vary over at least a 4 to 6 fold range depending on plant provenance. Intake of tannin at a high level reduces nutrient utilization, feed efficiency and animal productivity, however, in the present study CT concentration level of R. albersii, C. Molle , V. amygdalina and C. africana observed was within the safe range. Condensed tannins are generally known to affect negatively digestibility of forages if beyond a certain limit (about 6%) but also the type of CT may together with concentration play a great role (Abebe et al 2012; Schofield et al 2001).
|
Table 4. Gas production (ml/200gm DM) after 3, 6, 12, 24, 48h and gas production characteristics |
|||||||||||
|
Browse Trees |
Incubation period (hrs) |
Gas Production characteristics |
|||||||||
|
3 |
6 |
12 |
24 |
48 |
a |
b |
c |
a+b |
LT |
||
|
Wet season |
|||||||||||
|
C. africana |
2.5±2.12b |
9±1.41bc |
21±1.41b |
40±5.66a |
50±11.31ab |
-8.24±2.7b |
64.33±13.7b |
0.06±0.02ab |
56.09±16.32b |
2.5±0.71ab |
|
|
R. albersii |
7±1.41a |
19±4.24a |
34±0a |
50±2.83a |
55.5±0.71a |
-8.51±2.1b |
65.2±1.11b |
0.09±0.003a |
56.69±0.99b |
1.55±0.49ab |
|
|
P. capensi |
7±1.41a |
14±2.83ab |
28±5.66ab |
35±7.07ab |
49±1.41ab |
-1.1±5.11a |
58.98±8.92b |
0.06±0.05ab |
57.88±14.03b |
0.5±0.71b |
|
|
C. molle |
2.5±2.12b |
4.5±0.71cd |
11±1.41c |
24±0bc |
40±0bc |
-2.11±2.2ab |
77.57±4.67b |
0.02±0b |
75.46±6.43b |
1.6±1.56ab |
|
|
D. angustifolia |
1.5±0.71b |
4±2.83cd |
10±8.49c |
24±14.1bc |
34±8.49cd |
-4.93±4.1ab |
137.37±120.4b |
0.03±0.04b |
132.44±124.49b |
3±0.28a |
|
|
V. amygdalina |
1.5±0.71b |
3±1.41d |
5.5±2.12c |
14±2.83c |
24±0d |
-1.22±0.4a |
104±94.6b |
0.01±0.01b |
102.78±94.22b |
1.9±0.99ab |
|
|
C. collinum |
1.5±0.71b |
3±1.41d |
6±2.83c |
13±4.24c |
30±8.49cd |
-1.25±0.3a |
402.25±81.5a |
0.002±0b |
400.99±81.8a |
2±0.99ab |
|
|
F. thonningii |
2±1.41b |
3.5±2.12cd |
8±2.83c |
21±4.24bc |
34±0cd |
-2.48±0.4ab |
94.44±64.01b |
0.02±0.02b |
91.96±63.62b |
2.4±1.13ab |
|
|
Dry season |
|||||||||||
|
C. africana |
11±1.41b |
21±1.41b |
30±0b |
48±0ab |
65±1.41a |
4.02±1.14abc |
72.16±3.98ab |
0.04±0.01ab |
76.18±5.12ab |
NA |
|
|
R. albersii |
9±1.41bc |
12±0c |
27±1.41b |
39±1.41bc |
51±1.41b |
-0.25±1.57c |
56.1±3.76abc |
0.05±0ab |
55.85±2.19abc |
0.25±0.35b |
|
|
P. capensi |
4±0d |
8±0cd |
14±2.83d |
23±7.07d |
32±0c |
-0.36±4.52c |
62.44±34.82abc |
0.04±0.04ab |
62.08±39.34abc |
0.75±1.06ab |
|
|
C. molle |
5.5±0.71cd |
8±0cd |
12±2.83d |
21±4.24d |
30±5.66c |
2.32±0.82bc |
39.61±4.84bc |
0.03±0.01b |
41.92±4.02bc |
NA |
|
|
D. angustifolia |
11±1.41b |
18±5.66b |
23±7.08bc |
28±8.49cd |
37±9.9c |
8.19±0.31ab |
32±7.14c |
0.05±0.02ab |
40.19±6.83bc |
NA |
|
|
V. amygdalina |
20±2.83a |
29±1.41a |
43±1.41a |
51±1.41a |
62±2.83ab |
9.71±6.45a |
53.11±1.07abc |
0.08±0.03a |
62.82±5.38abc |
NA |
|
|
C. collinum |
8±0bc |
11±1.41c |
18±2.83cd |
37±4.24bc |
54±2.83ab |
1.32±1.07bc |
84.36±13.83a |
0.02±0.01b |
85.68±14.9a |
NA |
|
|
F. thonningii |
2.5±2.12d |
5±1.41d |
12±2.82d |
22±5.66d |
30±5.66c |
-2.64±0.49c |
37.99±5.57bc |
0.04±0.01ab |
35.36±6.07c |
1.8±0.71a |
|
|
Main effects |
|||||||||||
|
Season |
*** |
*** |
*** |
** |
** |
*** |
*** |
NS |
** |
*** |
|
|
Species |
*** |
*** |
*** |
*** |
*** |
* |
*** |
* |
*** |
NS |
|
|
Species x season |
*** |
*** |
*** |
*** |
*** |
* |
** |
NS |
** |
NS |
|
|
abcd Column means with different superscripts are significantly different (P<0.05); a = Gas production from the immediately soluble fraction (ml), b = Gas production from the insoluble but degradable fraction (ml), a + b = Potential gas production (ml); c =the rate constant of gas production (fraction/h); LT - lag time; *(P<0.05); ** (P<0.01); *** (P<0.001); NS (The effect is not significant P>0.05); Standard deviation (SD) NA (Not Available) |
|||||||||||
Table 4, Figure 1 and Figure 2 show the effects of season and browse species on Gas production(GP), the immediately soluble fraction (a), the insoluble but degradable fraction (b), degradation rate (c), potential gas production (a+b) and lag time (LT).
Among the eight browse species, R. albersii had the highest (P<0.05) GP, while V. amygdalina had low GP after 48hrs of the incubation period. Interaction between season and browse species had different trends for the variables. ForR. albersii, C. molle, F. thonningii and P. capensi, GP decreased from the wet to dry season. Whereas C. africana, V. amygdalina and C. collinum showed higher GP in the dry season than the wet season.
Browse tree species, P. capensi, V. amygdalina, and C. collinum shown the higher immediately soluble fraction (a) while R. albersii had lower. The C. collinum had the highest (P<0.05) potential gas production (a+b) while the other all browse species had similarly (P>0.05) lower. R. albersii had the fastest degradation rate(c), followed by P. capensi,C. africana, D. angustifolia, F. thonningii, C. molle, V. amygdalina and C. collinum. Moreover Dodenia angustifolia had the longest LT while P. capensi had the shortest LT.
The chemical composition (CP and fiber content) significantly influence degradation parameters and the positive relationship between GP and CP. The observed differences in gas production parameters among browse tree species indicated that there was a difference in rate and extent of fermentation characteristics. In all browse tree samples collected in the wet season and some of the same species studied in the dry season, the negative values of the readily degradable fraction (a) were recorded which agrees with earlier reports by (Bezabih et al 2013). The negative values could be due to differences in lag phase in the fermentation of insoluble feed components that lead to a deviation from the exponential curve of fermentation (Andualem et al 2016). The higher value of gas production from a slowly fermentable fraction (b) and the potential gas production (a+b) observed in C. collinum in both seasons and lower values for P. capensi andC. africana in the wet season and D. angustifolia and F. thonningii in the dry season could be associated with differences in protein content and fermentation pattern. The fermentation of protein reduces total gas production than carbohydrates (Getachew et al 2000; Andualem et al 2016).
The higher rate constant of gas production (c) observed in R. albersii and V. amygdalina in wet and dry seasons, respectively could be associated with the content of soluble components in these browse tree species. The values 0.027–0.044, for the fractional rate of gas production of the MPT under investigation show that they are highly digestible. The rate at which a feed or its chemical constituents are digested in the rumen is as important as the extent of digestion (Getachew et al 2000; Anele et al 2009; Andualem et al 2016).
|
| Figure 1. In vitro gas production of wet season multipurpose browse trees |
 |
| Figure 2. In vitro gas production of dry season multipurpose browse trees |
The organic matter digestibility (OMD), short-chain fatty acid (SCFA) and metabolizable energy (ME) of selected browse species are shown in (Table 5). The OMD, ME and SCFA had significant (P<0.05) differences among the browse species regardless of the season.
Interactions between season and species were observed for OMD (P<0.001), ME (P<0.001) and SCFA (P<0.001) (Table 5). R. albersii had the highest OMD, ME and SCFA values in the wet season, while C. africana and V. amygdalina had similar OMD, ME and SCFA values in the dry season.
Species affected (P<0.001) OMD and ME of the MPT. The result of the present study shown the highest values for OMD, ME and SCFA were observed during the dry season. The OMD and SCFA in V. amygdalina, R. albersii and C. africana similar (P>0.05) were higher than those in the other MPT, possibly because these browse trees contains more fermentable carbohydrate which is a vital substrate for growth of ruminal microorganisms [Anele et al 2009]. Relatively lower fiber fractions (Table 3) in some species the other MPT may have resulted in the higher values for OMD and SCFA (Van Soest, 1994). The variation of the ME values among the MPT was less than 1MJ/kg DM. The estimation of the ME values is valuable for purposes of ration formulation and to set the economic value of feeds for other purposes (Getachew et al 2002).
|
Table 5. Organic matter digestibility, metabolizable energy and short-chain fatty acids production |
|||
|
Browse Species |
Post incubation parameters |
||
|
OMD (%) at 48h |
ME(MJ/kgDM) |
SCFA(mmol/L) |
|
|
Wet season |
|||
|
C. africana |
82.8±8.04ab |
7.76±0.76a |
0.9±0.14a |
|
R. albersii |
90.2±0.55a |
9.15±0.39a |
1.13±0.07a |
|
P. capensi |
74.2±0.15bc |
7.08±0.98ab |
0.78±0.17ab |
|
C. molle |
64.6±0.25cd |
5.57±0.01bc |
0.51±0bc |
|
D. angustifolia |
61.1±8.09de |
5.6±1.94bc |
0.5±0.34bc |
|
V. amygdalina |
57.7±2.52de |
4.25±0.39c |
0.27±0.07c |
|
C. collinum |
56.7±6.66e |
4.08±0.58c |
0.25±0.1c |
|
F. thonningii |
69.6±3.04cd |
5.2±0.6bc |
0.44±0.44bc |
|
Dry season |
|||
|
C. africana |
95.6±0.92a |
8.84±0.01ab |
1.09±0ab |
|
R. albersii |
86.1±0.21ab |
7.67±0.19abc |
0.87±0.03bc |
|
P. capensi |
56.9±0.43cd |
5.39±0.95d |
0.49±0.17d |
|
C. molle |
54.8±6.51d |
5.13±0.59d |
0.44±0.1d |
|
D. angustifolia |
63.1±8.07cd |
6.13±1.16cd |
0.61±0.2cd |
|
V. amygdalina |
89.3±2.82a |
9.29±0.2a |
1.16±0.03a |
|
C. collinum |
77.6±3.26b |
7.33±0.59bc |
0.82±0.1bc |
|
F. thonningii |
67.3±4.78c |
5.32±0.76d |
0.47±0.14d |
|
Main Effect |
|||
|
Species |
*** |
*** |
*** |
|
Season |
* |
* |
** |
|
Species x season |
*** |
*** |
*** |
|
abcde Means in each column with the different letters are significant (p<0.05). SD: Standard deviation. Metabolizable energy (ME), Organic matter digestibility (OMD), Short Chain Fatty Acids (mmol); *(P<0.05); ** (P<0.01); *** (P<0.001); Standard deviation (SD) |
|||
The authors would like to acknowledge Dilla University, Energy and Environment Research Center for financing the research work.
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