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In vitro gas production kinetics of selected multipurpose tree browses in Gelana rangelands

Dereje Andualem, Mengistu Gelgele and Merga Bayssa1

a.dereje@yahoo.com
Dilla University, Department of Animal Science
1 Hawassa University, School of Animal and Range Sciences. Etiopia

Abstract

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


Introduction

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.


Material and methods

Description of the Study Area

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.

Identification and selection of browse species

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.

Browse trees foliage sample collection and preparation

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

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

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

Predicting biomass yield of selected multipurpose browse trees

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.

In vitro gas production

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 analysis

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.


Result and discussion

Biomass Yield and chemical composition

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
season

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
Season

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).

Effect of season on the chemical composition

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)

In vitro Gas production

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
Organic matter digestibility, metabolisable energy and short chain fatty

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)


Conclusion


Acknowledgements

The authors would like to acknowledge Dilla University, Energy and Environment Research Center for financing the research work.


References

Aganga A A and Adogla-Bessa T 1999 Dry matter degradation, tannin and crude protein contents of some indigenous browse plants of Botswana. Archivos de Zootecnia, 48, 79-83.

Alam M P and Djajanigara A 1994 Nutritive value and yield of potential tree leaves and shrubs in Bangladesh. In: Proceedings of 7th AAAP Animal Science Congress on Sustainable Animal Production and Environment. (Ed.): A. Sukmawati. Vol.2, held at Bali, Indonesia from July 6 to 11, 317-318.

Anele U Y, Arigbede O M, Südekum K H, Oni A O, Jolaosho A O, Olanite J A, Adeosun A I, Dele P A, Ike K A and Akinola O B 2009 Seasonal chemical composition, in vitro fermentation and in sacco dry matter degradation of four indigenous multipurpose tree species, Nigeria. Animal Feed Science and Technology, 154, 47–57.

Andualem D, Negesse T and Tolera A 2016 Methane Concentration, Organic Matter Digestibility, Metabolisable Energy and Short Chain Fatty Acid Production of Morphological Fractions of Stinging Nettle (Urtica simensis) Measured Through an In vitro Gas Test. Global Veterinaria 16, 276-284.

AOAC 1990 Official methods of analysis of the Association of Official Analytical Chemists, 15 edn. Association of official analytical chemists, Washington, Dc.

Abebe A, Tolera A, Holand Ø, Ådnøy T and Eik L O 2012 Seasonal Variation in Nutritive Value of Some Browse and Grass Species in Borana Rangeland, Southern Ethiopia. Tropical and Subtropical Agro ecosystems, 15, 261 – 271.

Bezabih M, Pellikaan W F, Tolera A, Khan N A and Henriks W H 2013 Chemical composition and in vitro total gas production and methane production of forage species from the mid rift valley grass lands of Ethiopia. Grass and Forage sciences, research gate.

Blümmel M, Aiple K P, Steingass H and Becker K 1999 A note on the stoichiometrical relationship of short chain fatty acid production and gas formation in vitro in feedstuffs of widely differing quality. Journal of Animal Physiology and Animal Nutrition, 81, 157-167.

Dalle G, Maass B L and Isselstein J 2006 Rangeland condition and trend in semi-arid Borana lowlands, Southern Ethiopia, African Journal of Range and Forage Sciences, 23, 49-58.

Debella E and Tolera A 2013 Nutritive value of Botanical Fractions of Moringa oleifera and Moringa stenopetela grown in the Mid-rift Valley of Southern Ethiopia. Agroforestry Systems, 87, 1147-1155.

Devendra C 1993 Trees and shrubs as sustainable feed resource. Proceedings VII world conference on animal production, Edmonton, Canada, 1: 119-138.

Gaiballa A K and Lee S J 2012 Importance of Indigenous Browse Species in Improvement of Livestock Feeds in Western Bahr El Ghazal State (Sudan). Journal of Science and Technology Vol. 13, 39-51.

Getachew A 2005 Evaluation of forage yield and effect forms feeding of acacia saligns L. on intake and live weight gain by sheep fed a basal diet of maize stover. Animal Feed Science and Technology, 46, 97-108.

Getachew G Makkar H P S and Becker K R 2000 Stoichiometric relationship between short chain fatty acid and in vitro gas production in presence and absence of polyethylene glycol for tannin containing browses, EAAP Satellite Symposium containing browses, EAAP Satellite Symposium evaluation and to assess microbial activity,;18-19 August, Wageningen, The Netherlands.

Getachew G, Crovetto GM, Fondevila M, Krishnamoorthy U, Singh B, Spanghero M., Steingass H, Robinson P H and Kailas M M 2002 Laboratory variation of 24 h in vitro production and estimated metabolizable energy values of ruminant feeds. Anim. Feed Science and Technology 102, 169–180.

Hedberg I and Edwards S 1989 Flora of Ethiopia. Vol. 3. The National Herbarium, Addis Ababa, Ethiopia. 660p.

Kassahun D, Yoseph M and Getnet A 2016 Identification and nutritional value assessment of the major browse Species in Chilega District, North Gondar. Global Veterinaria 16, 06-17.

Kellems R O and Church D C 1998 Livestock Feeds and Feeding (4th edition). Prentice-Hall Inc., New Yersey, USA, pp.537.

Makkar H P S 2003 Quantification of tannins in tree and shrub foliage: A laboratory manual, Dordrecht, Germany Kluwer Academic Publishers. 102p.

McDonald P, Edwards R A, Greenhalgh J F D and Morgan C A 2002 Animal Nutrition (6th edition). Pearson Educational Limited. Edinburgh, Great Britain. 544p.

Meissner H H, Viljoen M D and Van Nierkeki W A 1991 Intake and digestibility by sheep of Anthephora, Panicum, Rhode and Smuts finger grass pastures: Proceeding of the 4th International Rangeland Congress, France.

Menke KH, Raab L, Salewski A, Steingass H, Fritz D and Schneider W 1979 The estimation of the digestibility and metabolizable energy content of ruminant feedstuffs from the gas production when they are incubated with rumen liquor in vitro. Journal of Agricultural Science, 92, 217-222

Norton B W 2003 Studies of the nutrition of the Australian goat. Thesis (D. Agr. Sc), University of Melbourne, Australia. 594p

Ørskov E R and McDonald I 1979 The estimation of protein degradability in the rumen from incubation measurements weighted according to rate of passage. Journal. of Agricultural Science, 92, 499-503.

Petmak M V 1983 Primary Productivity, Nutrient Cycling and Organic Matter turnover of Tree Plantation after Agricultural Intercropping Practices in Northeast Thailand. PhD thesis, University of the Philippines, Los Baños, Philippines, pp: 228.

SAS 2008 SAS/STAT® 9.2 User’s guide. SAS Inst Inc, Cary, NC, USA.

Schofield P, Mbugua D M and Pell A N 2001 Analysis of condensed tannins: a review. Animal Feed Science and Technology, 91, 21-40.

Van Soest P J, Robertson J B and Lewis B A 1991 Methods for dietary fibre, neutral detergent fibre and non-starch carbohydrates in relation to animal nutrition. Journal of Dairy Science, 74, 3583-3597.

Van Soest P J 1994 Nutritional Ecology of the Ruminant, 2nd ed. Comstock Publishing Associates/Cornell University Press, Ithaca, NY, USA.