Seasonal variations in chemical composition, in vitro digestibility and ruminal degradation of browse species in the Rift Valley of Ethiopia

Ahmed Hassen¹, Zewdu Kelkay Tessema and Adugna Tolera²

School of Animal and Range Sciences, Haramaya University, P O Box 138, Dire Dawa, Ethiopia
tessemazewdu@gmail.com
¹ Department of Animal Science, Debre Berhan University, P O Box 445, Debre Berhan, Ethiopia
² Department of Animal and Range Sciences, Hawassa University, P O Box 222, Hawassa, Ethiopia

Abstract

An experiment was conducted to evaluate the effect of season on chemical composition, in vitro dry matter digestibility (IVDMD), total phenol and tannin contents, and in sacco dry matter degradability (DMD) of common browse species grown in the semi-arid Rift Valley areas of Ethiopia. Leaf samples were collected during the main rainy and dry seasons from eleven browse species.

Almost all browse species had a moderate to high crude protein (CP) content (52.4 - 220 g/kg DM), moderate neutral detergent fiber (283 - 552 g/kg DM) and acid detergent fiber (128 - 433 g/kg DM) contents and a high IVDMD (623 - 678 g/kg DM) and metabolisable energy values (8.80 - 9.70 MJ/kg DM) during the wet season. The CP content of browse species significantly decreased during the dry season compared to wet season. The total phenol and tannin contents were lower in wet than the dry season. Among the browse species, Jasminum grandiflorum had the highest soluble fraction and effective degradability, while Prosopis juliflora had the highest insoluble but potentially degradable fractions during wet season. The browse species could be used as supplementary feed during the dry season to low quality natural pastures and crop residues in the study areas. However, high tannins and total phenols concentration in some browse species may limit their feeding value unless supplemented with nutritious and less tanninferous feed resources.

Key words: anti-nutritional factor, degradability characteristics, rangeland, roughage feeds, season

Introduction

Rangelands play a significant role as a primary source of feed for livestock and wild herbivores in semi-arid areas of the world. However, semi-arid rangelands in most parts of the world experience different forms of land and vegetation degradation, as a result of continuous heavy grazing, existing climate change/variability, and land use changes (Kassahun et al 2009). Hence, the disappearances of good fodder grasses are major challenges in semi-aid rangelands for both wild and domestic herbivores (Tessema et al 2011). The problem is exacerbated by seasonal variation in forage quality, which show low energy, protein, minerals and vitamins contents during the dry season and drought periods (Tessema and Baars 2004; Murthy et al 2011), which may not satisfy the nutritional requirement of animals for maintenance and production. Moreover, livestock feed supply has been further constrained by invasion of less palatable thorny bushes such as Prosopis juliflora, which are heavily replacing the more nutritious browse and herbaceous plant species in semi-arid rangelands (Joanne et al 2005).

Indigenous browse species, including trees and shrubs, adapted to the existing climatic variability, are becoming the major feed resources in semi-arid rangelands by supplying protein and energy to maintain livestock production (Anele et al 2009). They reduce seasonal feed resource limitation since they remain green during dry season, produce more biomass, and are more nutritious than natural grazing lands (Anele et al 2009; Shenkute et al 2012). In comparison to grasses, browse species are less affected by climatic variability due to their extensive root system and long life-span. In addition, they serve as a shelter and fuel as well as maintain and improve the soil fertility of semi-arid rangelands. However, browse species may have high concentration of secondary plant metabolites such as tannins and phenols, which may act as anti-nutritional substances and that could limit their utilization (Belachew et al 2013; Basha et al 2015), thereby affecting the livelihood of livestock herders (Njidda and Ikhimioya 2012).

Previous studies evaluated the effects of season and tannin content on nutritional quality of some indigenous browse species in Ethiopia (Tolera et al 1997; Yayneshet et al 2009; Aster et al 2012). However, there are many more browse species whose potential uses as supplementary feed for livestock that need to be studied. Moreover, their species composition and nutritional values differs due to variation in topography, elevation, rainfall distribution, soil fertility and management conditions. In addition, changes in composition of browse species could also occur due to rangeland degradations, as a result of climate change/variability, and land use changes in most parts of semi-arid grazing lands in Ethiopia. Therefore, we studied the chemical composition, in vitro dry matter digestibility (IVDMD), and anti-nutritional contents, as well as in sacco rumen dry matter degradation (DMD) and degradability characteristics of major browse species harvested in wet and dry seasons in the Ethiopian Rift valley, a typical feature of semi-arid ecosystems of the world.

Materials and methods

Description of the study area

Representative samples of common browse species were collected from Mieso district of Oromia region, in the Rift Valley area of Ethiopia, for this study. Mieso district is located at an altitude range of 823–2475 m above sea level, between 40^°56’ and 40°9’E longitude and between 8^°48 and 9^°19’N latitude at a distance of about 325 km to the east of Addis Ababa, the capital of Ethiopia. The study site has an average annual rainfall of 752.3 mm, with variable distribution. Under normal condition, there are two rainy and one long dry season in the district. The short and long rainy seasons last from February to May and from June to September, respectively, whereas the long dry season occurs from October to January. Observation of rainfall trends during the last three decades (1984-2015) shows that the short rainy season usually fails and not as frequent as the main rainy season with the coefficient variation of 33.4% (Figure 1). As a result, recurrent drought is a major problem in the study areas. The mean daily minimum and maximum temperatures from 1984 - 2015 were 12.9^oC and 37.1^oC, respectively. The number of rainy days per month is the highest in August (27 days). The district includes both pastoral communities, where livestock rearing is the main livelihood of the people and dependent up on communal grazing systems on rangelands as feed resources (Jeffrey et al 2011). Cattle, sheep, goats and camels are the major livestock species owned by the livestock herders (pastoralists) in the study district. Cultivation of crops, mainly sorghum and maize has been introduced to the district as an opportunistic activity due to the erratic nature and unreliable rainfall distribution.

Figure 1. Average rainfall, minimum and maximum temperature of the study area,
Mieso district in the Rift Valley of Ethiopia, 1984-2015

Sample collection and preparation

Two representative kebelles (the smallest administrative units under district) were purposely selected on the basis of rangeland potential, presence of major browse species based on group discussion with livestock herders and in consultation with extension agents and livestock development experts in the district. Representative browse species were selected based on preference by the livestock herders, their distribution (abundance) and accessibility to livestock, as well as according to the procedures of previous studies on browse species in Ethiopia (Yayneshet et al 2009; Yisehak et al 2010; Aster et al 2012). Accordingly, samples of eleven most dominant browse species namely,Acacia robusta (Burch.), Carissa spinarum (L.), Combretum molle (R. Br., ex G. Don), Commicarpus plumbagineus (cav., standley), Cordia monoica (Roxb.), Grewia ferruginea (Hochst. Ex A. Rich.), Grewia tembensis (Foesen.), Jasminum grandiflorum (L. subsp.), Opuntia ficus-indica, Prosopis juliflora (Sw.) DC., Rhus natalensis (Krauss) were collected over two seasons, in September and February representing wet and dry seasons, respectively. Samples of leaves were randomly harvested from 10-15 plants of each browse species and pooled to make a composite sample per species. After making a composite sample, triplicate samples were weighed immediately, transferred into plastic bags and taken to the Animal nutrition laboratory at Haramaya University of Ethiopia within six hours and oven dried at 65˚c for 72 hours. The dried samples were ground in a Wiley mill to pass through 1mm sieve for chemical analyses and IVDMD determination and through 2 mm sieve size for in sacco DM degradability study.

Chemical analyses and IVDMD determination

The samples were analyzed for dry matter (DM), nitrogen (N) and ash using the standard procedures of AOAC (1990). Crude protein (CP) was calculated as N x 6.25. Neutral detergent fiber (NDF) was determined by the method of Van Soest et al (1991) whereas acid detergent fiber (ADF) and acid detergent lignin (ADL) were analyzed according to Van Soest and Robertson (1985). Sulphite and α - amylase were not included in the neutral detergent solution used for NDF determination. Both NDF and ADF were expressed without residual ash. Hemicellulose and cellulose were calculated as NDF minus ADF and ADF minus ADL plus ADF-ash, respectively. The total phenol content for browse species was determined according to Julkunen-Tiitto (1985) and tannin was determined following the procedure of Makkar (2003).

In vitro dry matter digestibility (IVDMD) was determined according to Tilley and Terry (1963) as modified by Van Soest and Robertson (1985), in which the second stage (pepsin digestion) is substituted with neutral detergent solution. This treatment removes all the indigestible microbial matter and leaves as residue of undigested plant cell wall and the values represent true digestibility. The modified procedure is precise and requires half of the time to complete the whole procedure (two days shorter) compared to the original Tilley and Terry procedures. Metabolisable energy (ME) was estimated using the equation for tropical forages: ME (MJ/kg DM) = DOM (g/kg DM) x 18.5 x 0.81, where digestible organic matter (DOM) was calculated as 0.95IVDMD% - 2 (AAC 1990).

In sacco DM degradability

In sacco DM degradability (DMD) was determined by incubating a 3 g of dry feed sample (2 mm sieve) in pre-weighed nylon bags (40-42 μ m pore size and ~5 cm x 15 cm dimension) in three rumen fistulated Boran x Holstein Friesian steers at Holeta Agricultural Research Center (HARC), Ethiopia. The crossbred steers were kept in door and fed natural pasture hay adlibitum (CP = 520 g/kg, NDF = 635 g/kg), and 2 kg of concentrate (formulated from wheat bran (55%), noug seed cake (43%) and salt (2%) (CP = 230 g/kg, NDF = 206 g/kg) once daily whereas water was accessible all the time throughout the experimental period, which assumed to fulfill all the nutrient and energy requirement of the animals. Bags were incubated 1 h after the steers were offered feed and withdrawn sequentially after 6, 12, 24, 48, 72 and 96 h of incubation. Upon removal from the rumen, bags were immediately washed carefully five times for 6 min using tap water and dried for 48 h at 60 ^oC. Washing losses were determined by soaking three bags per sample in warm tap water (60^oC) for 48 h followed by washing and drying.

The DMD data were fitted to the exponential equation: Y = a + b (1 – e^–ct⁾ (Ørskov and McDonald 1979) where Y is DMD at time of t. The effective degradability (ED) characteristics was calculated using the formula ED = a + [bc/(c + k)] (Dhanoa 1988), where a, b and c as described above and k is the rumen outflow rate, assumed to be 0.04/h (Ørskov et al 1988). Potential degradability (PD) was calculated as a + b.

Statistical analyses

The chemical composition, IVDMD, total phenol and tannin concentration and in sacco DMD data were subjected to analysis of variance using a General Linear Model procedure of statistical analysis system (SAS) statistical software version 9.1 (SAS 2008). The model used was Yi = µ + Zi + Sj + Pk+ eijk, where Y is the dependent variable, µ is the overall mean, Zi is browse species effect, Sj is the season effect, Pk is the interaction between species and season and eijk is the random residual error assumed to be normally and independently distributed. Tukey- HSD test was used to determine mean differences at P≤0.05.

Results

Chemical composition and IVDMD of browse species

The chemical composition of browse species were significantly (P<0.001) influenced by species, season and their interaction (Table 1). The CP content of all studied browse species was significantly higher during wet season compared to the dry season, while the reverse was true for NDF, ADF and ADL, showing overall significant differences (P<0.001) between species and seasons. The CP values among the eleven browse species ranged from 52.4 - 220 g/kg DM during wet season and from 32.4 - 169 g/kg DM during the dry season. In both seasons, the highest CP content was recorded in C. spinarum, whereas the lowest was in O. ficus indica. The NDF and ADF contents were highest in O. ficus-indica and lowest in C. spinarum. The mean IVDMD values of the studied browse species generally was higher in the wet season (ranged from 623 - 678 g/kg DM) than in the dry season (ranged from 508 - 658 g/kg DM). The mean ME content also varied from 8.80 - 9.70 MJ/kg DM in wet season and from 7.30 - 9.40 MJ/kg DM in the dry season. The highest INDMD and ME values were observed in C. spinarum in both wet and dry seasons whereas O. ficus-indica exhibited the lowest IVDMD and ME values in both seasons. Neutral detergent fiber, ADF, ADL, cellulose and ash values were higher in the dry season than in the wet season with significant differences among species within each season (Table 1). The ash content was higher in the dry season than in the wet season and ranged from 92.6 - 163 g/kg DM and 67.1 - 126 g/kg DM, respectively. The highest ash content was observed in C. plumbagineus (126.2 g/kg DM) and followed by C. monoica (116 g/kg DM) in the wet season, whereas the lowest ash content (67.1 g/kg DM) was observed in C. spinarum followed by O. ficus indica (72.2 g/kg DM) in the wet season. The hemicellulose and cellulose contents of browse species varied from 54.0 - 191 g/kg DM and 58.7 – 279 g/kg DM, respectively in wet season. However, dry season had a higher hemicellulose and cellulose values than wet season among the studied browse species (Table 1).

Total phenol and tannin contents of browse species

Species and season had a significant (P<0.001) effect on total phenols and tannin contents (Table 2), as their concentration increased during dry season than wet season. The interaction between season and species on total phenol and tannin contents was not significant (P>0.052). The total phenol content of browse species ranged from 7.60 - 36.7 mg/100g and from 9.40 - 39.5 mg/100g DM during wet and dry season, respectively. The highest phenol content (36.7 mg/100g DM) was recorded in G. ferruginea followed by A. robusta (31.4 mg/100g DM), whereas the lowest phenol content (7.60 gm/100g DM) was reported in C. spinarum in both dry and wet seasons. The tannin content was within the range of 35.0 - 696 and 46.8 - 709 mg/100g DM during the wet and dry season, respectively. G. ferruginea had significantly a higher (P<0.050) phenol and tannin contents in both seasons. The lowest concentration of tannin was reported in P. juliflora (35.0 mg/100g DM) harvested during wet season, whereas R. natalensis ranked second in tannin content after G. ferruginea in our study.

Table 1. Chemical composition (g/kg DM) and in vitro dry matter digestibility (g/kg DM) of browse species during the wet and dry season, in Mieso district of the Rift Valley of Ethiopia
Browse species	CP	ASH	NDF	ADF	ADL	Hemicellulose	Cellulose	ME	IVDMD

Wet season
Acacia robusta	150^ef	78.6^m	414^gh	161^u	66.3ⁿ	183^c	94.9^p	9.40^b	662^c
Carissa spinarum	220^a	67.1^o	283^k	128^v	63.2^o	155^e	58.7^s	9.70^a	679^a
Combretum molle	182^c	87.9^l	332^j	193^t	105^l	191^a	71.2^r	9.30^bc	656^e
Commicarpus plumbagineus	140^h	126^e	400^def	233^s	146^gh	187^b	87.8^q	9.50^ab	676^a
Cordia monoica	129ⁱ	116^g	420^fgh	274^o	178^b	176^d	96.3^p	9.51^ab	673^b
Grewia ferruginea	103^kl	112^h	449^def	362^f	160	138^g	132ⁿ	8.83^d	623^k
Grewia tembensis	191^b	95.5^j	391^hi	249^r	123^j	142^f	126^o	9.32^bc	654^e
Jasminum grandiflorum	154^e	103ⁱ	427^efg	294^l	156^e	133^hi	138^m	9.14^c	636^h
Opuntia ficus indica	52.4^o	72.2ⁿ	552^b	433^b	154^e	119^kl	279^b	9.16^c	632ⁱ
Prosopis juliflora	151^e	86.6^l	395^hi	341^g	114^k	54.0^q	227^d	9.40^b	664^c
Rhus natalensis	146^fg	88.4^l	459^cd	283ⁿ	126ⁱ	126^j	127^o	8.85^d	626^j
Dry season
Acacia robusta	111^j	102ⁱ	381ⁱ	252^q	88.0^m	130^j	166^j	9.33^bc	649^f
Carissa spinarum	169^d	132^d	323^j	260^p	86.2^m	62.8^p	172^h	9.46^b	658^d
Combretum molle	145^g	114^h	421^fgh	290^m	149^f	131^hi	141^m	8.42^e	592^o
Commicarpus plumbagineus	101^l	159^b	463^cd	329ⁱ	161^d	134^gh	168ⁱ	8.81^d	620^l
Cordia monoica	92.9^m	163^a	481^c	391	195^a	90.5ⁿ	197^f	9.10^c	635^hi
Grewia ferruginea	81.0ⁿ	144^c	457^cde	338^h	156^e	118^l	183	8.57^e	604ⁿ
Grewia tembensis	139^h	124^ef	421^fgh	298^k	144^h	122^k	155^l	9.38^bc	645^g
Jasminum grandiflorum	113^j	141^c	461^cd	386^e	175^c	74.8^o	212	8.19^f	571
Opuntia ficus indica	32.4^p	92.6^k	585^a	495^a	172^c	90.1ⁿ	323	7.36^g	508^q
Prosopis juliflora	78.2 ⁿ	123^f	435^defg	398^c	148^fg	37.6^r	250^c	8.54^e	603ⁿ
Rhus natalensis	106^k	118^g	418^gh	315^j	157^e	103^m	159^k	8.82^d	615^m
SEM	1.07	0.990	10.5	0.980	0.950	1.25	0.950	0.094	0.971
Season	0.001	0.001	0.001	0.001	0.001	0.001	0.001	0.001	0.001
Species	0.001	0.001	0.001	0.001	0.001	0.001	0.001	0.001	0.001
Season*Species	0.001	0.001	0.002	0.001	0.001	0.001	0.001	0.001	0.001
SEM = standard error of the means; CP = crude protein; NDF = neutral detergent fiber; ADF = acid detergent fiber; ADL= acid detergent lignin,; ME, metabolisable energy; IVDMD = in vitro DM digestibility; Means with different letters within column are significantly different at P≤0.05

In sacco DMD of browse species

Species, season and their interactions had highly significant (P<0.001) effects on the DMD values of browse species at all incubation periods (Table 3). The DMD values of browse species were higher in wet season than in the dry seasons and increased with increasing incubation periods in all browse species (Table 3). Inter-species variation for DMD values of browse species at different incubation hours indicated that the highest (P<0.001) DMD was observed in A. robusta at 0 and 96 h, inJ. grandiflorum at 6 and 12 h, inCommicarpus plumbagineus at 24 h, in C. plumbagineus andC. monoica at 48 h, and in A. robusta and C. plumbagineus at 72 h. On the other hand, the lowest (P<0.001) DM disappearance was observed inO. ficus indica, P. juliflora and G. tembensis at 0 h, inP. juliflora at 6 h, in C. plumbagineus at 12 h, and O. ficus indica from 24 to 96 h of incubation periods.

Species and season had also a significant (P<0.001) effect on the DM degradability characteristics (Table 4). However, the interaction between species and season did not have significant effect on DM degradability characteristics except on the degradability value of the slowly degradable fraction. All browse species had higher DM degradability characteristics in the wet season than in the dry season. The soluble or rapidly degradable fraction (a value) was highest (P<0.001) in J. grandiflorum in the wet season and lowest in O. ficus indica in the dry season (Table 4). On the other hand, the slowly degradable fraction (b value) was lowest in J. grandiflorum and highest in P. juliflora during the wet season. The rate of degradation (c value) was highest (P<0.01) in G. tembensis and lowest in C. plumbagineus in the dry season. The PD and the ED values were highest in C. plumbagineus and J. grandiflorum in the wet season, whereas the lowest values for both variables were recorded in O. ficus indica in the dry season. The PD characteristics values of browse species ranged from 616 - 678 g/kg DM in wet season and from 552 - 652 g/kg DM during the dry season in our study. Among the browse species, C. plumbagineus had the highest PD fractions in both wet and dry seasons (Table 4).

Discussion

Chemical composition and IVDMD values of browse species

The chemical composition of the browse species reported in this study lie within the ranges reported for other indigenous browse species (Tolera et al 1997; Anele et al 2009; Yayneshet et al 2009; Belachew et al 2013). The significant effect of season on the chemical composition and IVDMD of browse species might be due to reduced uptake of essential nutrients from the soil and reduced photosynthetic activities of the plants induced by environmental stress during the dry season. The lower CP content of the browse species harvested during the dry season as compared to the wet season could be due to advancement in age of the plant associated with leaf maturity, lower moisture content of the soil and availability of less nitrogen, and higher proportion of fibre fraction (Belachew et al 2013). On the other hand, a higher CP content during the wet season compared to dry season might be due to higher photosynthetic rate and higher moisture content which increase nitrogen uptake (Anele et al 2009). Moreover, browse trees shed their leaves during dry season, as a result the photosynthetic rates are reduced and food reserves are translocated from leaves to stem and root parts (Turner et al 2007). Thus, the reduced CP during the dry season is associated with low water availability and slow rate of photosynthesis. The findings conform to the reports of previous studies (Yayneshet et al 2009; Aster et al 2012) who reported seasonal variations in nutritional value of browse species, with lower values of CP reported for plants with advanced age and during moisture stress.

Among the browse species, C. spinarum had the highest CP, ME and IVDMD values and the lowest NDF, ADF, ADL and cellulose contents in both wet and dry seasons. The entire browse species evaluated in this study, except O. ficus indica, had CP contents of higher than 70 g/kg DM across seasons, which indicates that most of the species can be used as supplementary feeds to enhance utilization of low quality feed resources and improve the performance of ruminants during the dry season. However, in the case of O. ficus indica, the CP content is as low as 52.4 g/kg DM in the wet season, which further decreases to 32.4 g/kg DM in the dry season. Thus, the feeding of O. ficus indica could reduce feed intake, rumen microbial condition and function (Van Soest, 1994) unless it is supplemented with other browse species to satisfy the need of adequate nitrogen required by rumen microorganisms.

The IVDMD value (632- 679 g/kg DM) obtained from browse species in this study was comparable with the reports of Yayneshet et al (2009) (620 – 740 g/kg DM), and lower than the values reported by Aster et al (2012) (676 – 975 g/kg DM) during wet season. This difference could be a result of wide variations in topography, elevation, rainfall distribution, soil fertility and management conditions and possibly differences in the stage of maturity. The mean ME values were higher in the wet season (9.26 MJ /kg DM) than the dry season (8.68 MJ /kg DM), which is in agreement with Yayneshet et al (2009) who reported higher ME (10.3 MJ /kg DM) during wet season and lower ME (9.16 MJ /kg DM) during dry season.

The NDF contents of all browse species in this study were fell below 600 g/kg DM, a level above which feed intake of ruminants is affected (Meissner et al 1991). The decrease in the CP, ME and IVDMD and an increase in NDF, ADF, ADL and cellulose contents in most of the browse species during dry season could be due to lower moisture content and arrested photosynthetic activities of the plants during the dry season (Yayneshet et al 2009; Belachew et al 2013; Basha et al 2015).

Total phenol and tannin contents

The higher concentration of secondary plant metabolites including total phenols and condensed tannins in the dry season compared to the wet season may be associated with increased stress due to high temperature and low moisture availability and increased maturity of the plants (Onyeonagu et al 2013). The tannin concentration observed in this study was within a range of 46.8 –709.1 mg/100g DM during the dry season. Various studies (Silanikove et al 1996; Njidda and Ikhimioya, 2012) demonstrated that moderate concentration of condensed tannins (2 - 4%) is favorable for improving protein utilization by ruminant animals by preventing excessive rumen degradation of protein and increasing the amount of rumen escape or bypass protein that will be digested in the small intestine.

In sacco DM degradability

The in sacco DM disappearance values obtained in this study were within the range of values reported by Aster et al (2012) for different browse species from the Borana rangelands of southern Ethiopia but higher than the values reported by Belachew et al (2013) for browse species. Moreover, significant differences in in sacco DMD were observed among the different browse species, which could be associated with difference in chemical composition (Anele et al 2009). The DM disappearance was lower during dry season than the wet season is consistent with the findings of Aster et al (2012) but contrary to that of Basha et al (2015) who reported higher DM degradability during the dry season. The seasonal difference in DM degradability of the browse species observed in the current study can be attributed to seasonal differences in accumulation of structural components, differences in the stage of maturity and possibly wider climate and edaphic differences.

The DM degradability constants (a, b and c) were significantly influenced by season and species. Higher rapidly degradable fraction (a) was recorded in J. grandiflorum in both seasons than other browse species. The soluble degradable fraction (b) in this study was lower than that of Basha et al (2015). This may be associated with seasonal variation in chemical composition between plant species. Soluble fractions, PD and ED differences among species and seasons could be associated with differences in CP, NDF, ADF, ADL, tannin and phenol contents. For instance, C. spinarum had higher CP, ED and PD and lower in fiber and anti-nutritional factor in the two seasons. These results agreed with Balgees et al (2013) who reported that the rate of degradation of protein was negatively related to NDF and ADF concentration. Basha et al (2015) also reported that ED were positively correlated with CP but negatively related with fiber fractions and condensed tannin.

Among the browse species, O. ficus-indica had the lowest soluble fraction, PD and ED with average rate of passage (0.06) and high content of insoluble but slowly degradable fractions. This could be attributed to low content of CP, ME and IVDMD in this species compared to other browse species, as this probably might affect rumen microbial function and reduce forage intake due to lower rate of degradation and increase in rumen fill (Tessema and Baars, 2004). However, pastoralists and agro-pastoralists in the study area appreciate the importance of O. ficus-indica because of its availability during the dry season in drought prone areas when livestock regularly suffers from shortage of feeds. The provision of O. ficus-indica with high nitrogen source browse species could provide adequate energy and nitrogen for micro-organisms in the rumen and for effective utilization of the available feed resources.

Conclusions

Acknowledgement

The authors would like to acknowledge the Haramaya University of Ethiopia for the financial and material support during the field and laboratory studies. We also acknowledge the Holetta Agricultural Research Center (HARC) of Ethiopia for providing analytical services.

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Table 2. Concentration of total phenols and tannins (mg/100g DM) of browse species during the wet and dry season, in Mieso district of the Rift Valley of Ethiopia
Browse species	Total phenol content (by Gallic acid equivalence)	Tannin content (by Catechin equivalence)

Wet season
Acacia robusta	31.4^c	78.4^efgh
Carissa spinarum	7.61^m	94.3^def
Combretum molle	15.5^ijkl	70.2^fghij
Commicarpus plumbagineus	12.6^l	70.4^fghij
Cordia monoica	15.0^jkl	39.3^jk
Grewia ferruginea	36.7^b	696^a
Grewia tembensis	14.2^kl	93.7^def
Jasminum grandiflorum	19.8^fghi	56.5^ghijk
Opuntia ficus indica	16.5^ijkl	72.0^efghi
Prosopis juliflora	24.3^ef	35.0^k
Rhus natalensis	22.1^fgh	146^bc
Dry season
Acacia robusta	34.5^b	87.0^def
Carissa spinarum	9.42^lm	115^cd
Combretum molle	17.2^efgh	79.2^efgh
Commicarpus plumbagineus	14.7^hij	86.8^defg
Cordia monoica	16.2^ghi	54.1^hijk
Grewia ferruginea	39.5^a	709^a
Grewia tembensis	15.1^de	102^de
Jasminum grandiflorum	24.5^c	68.8^fghijk
Opuntia ficus indica	19.2^efg	84.2^defgh
Prosopis juliflora	26.2^cd	46.8^ijk
Rhus natalensis	24.2^ef	159^b
SEM	1.53	10.7
Species	0.001	0.010
Season	0.001	0.001
Species*season	NS	NS
SEM = standard error of the means; NS = non-significant Means with different letters within column are significantly different at P≤0.05

Table 3. In sacco ruminal dry matter degradability (DMD, g/kg DM) of browse species during the wet and dry season at different rumen incubation times, in Mieso district of the Rift Valley of Ethiopia
Browse species	Incubation times (in hours)
Browse species	0	6	12	24	48	72	96

Wet season
Acacia robusta	192^a	376^c	480^b	567^ab	635	661^a	689^a
Carissa spinarum	169^d	360^d	472^c	569^ab	637^b	652^cd	658^f
Combretum molle	174^c	314^j	444^g	568^ab	635^b	655^b	667^d
Commicarpus plumbagineus	145^f	341^f	449^f	569^a	642	661^a	679^b
Cordia monoica	111^j	319^h	453^e	563^c	641	650^cd	655^f
Grewia ferruginea	151^e	357^e	460^d	567^ab	632	649^d	655^f
Grewia tembensis	187^b	377^c	478	567^b	634^b	651^cd	657^f
Jasminum grandiflorum	123^h	426^a	487^a	559^b	631^c	651^cd	664^e
Opuntia ficus indica	104^kl	264^o	402^l	512^d	592ⁱ	601^h	624^k
Prosopis juliflora	103^kl	294^lm	413^k	537^j	612^e	625^e	649^h
Rhus natalensis	150^e	327^g	441^h	562^f	632^c	653^bc	672^c
Dry season
Acacia . robusta	128^g	341^f	443^gh	512^c	586^j	612^f	634^j
Carissa spinarum	101^l	318^hi	448^f	527^j	584^j	605^g	643ⁱ
Combretum . molle	111^j	291^m	413^k	520^g	577^k	625^e	613^m
Commicarpus plumbagineus	105^k	306^k	357^p	521ⁱ	612^e	614^f	652^g
Cordia monoica	98.6^m	286ⁿ	395^m	513^j	626^d	587^j	615^m
Grewia ferruginea	114ⁱ	316^ij	421^j	522^h	603	595ⁱ	598ⁿ
Grewia . tembensis	93.1ⁿ	341^f	437ⁱ	518ⁱ	609^f	597ⁱ	586^o
Jasminum grandiflorum	102^l	395^b	478^b	508^k	596^h	625^e	615^l
Opuntia ficus indica	91.2ⁿ	219^p	375^o	426^m	538^m	526^l	571^p
Prosopis juliflora	92.3ⁿ	207^q	389ⁿ	488^l	579^k	579^k	595ⁿ
Rhus natalensis	101^l	294^l	402^l	546^e	543^l	615^f	624^k
SEM	1.10	0.981	0.983	1.15	0.983	1.04	1.01
Species	0.001	0.001	0.001	0.001	0.001	0.001	0.001
Season	0.001	0.001	0.001	0.001	0.001	0.001	0.001
Species* season	0.001	0.001	0.001	0.001	0.001	0.001	0.001
Means with different letters within column are significantly different at P≤0.05.

Table 4. In sacco dry matter degradability (DMD) characteristics (g/kg DM) of browse trees and shrubs harvested during the wet and dry season in Mieso district of the Rift Valley of Ethiopia
Browse species	Degradability characteristics of browse species
Browse species	a	b	c	PD	ED

Wet season
Acacia . robusta	195^h	473^e	0.072^abc	667^b	530^b
Carissa spinarum	221^d	432^m	0.061^bcd	653^d	522^cd
Combretum . molle	184ⁱ	480^d	0.063^bcd	664^c	508^e
Commicarpus plumbagineus	237^c	441^jk	0.050^cd	678	520^d
Cordia monoica	204^f	449ⁱ	0.062^bcd	653	508^e
Grewia ferruginea	250^b	413^o	0.054^cd	662^c	521^cd
Grewia . tembensis	172^k	472^e	0.083^ab	644^e	522^c
Jasminum grandiflorum	275^a	378^q	0.061^bcd	652^d	537^a
Opuntia ficus indica	119^m	497^b	0.060^bcd	616ⁱ	459^k
Prosopis juliflora	132^l	507^a	0.064^bcd	638^f	480^h
Rhus natalensis	209^e	459^gh	0.051^cd	668^b	510^e
Dry season
Acacia . robusta	177^j	437^kl	0.072^abc	615ⁱ	485^g
Carissa spinarum	199^g	422ⁿ	0.060^bcd	621^g	486^g
Combretum . molle	175^j	442^j	0.053^cd	618^h	470^j
Commicarpus plumbagineus	194^gh	456^h	0.041^d	652^d	470^j
Cordia monoica	184ⁱ	436^l	0.054^cd	620^g	469^j
Grewia ferruginea	206^e	340^p	0.063^bcd	606^k	477ⁱ
Grewia . tembensis	130^l	465^f	0.091^a	594^l	479^hi
Jasminum grandiflorum	235^c	375^q	0.072^abc	610^j	505^f
Opuntia ficus indica	92.1^o	460^g	0.060^bcd	552^m	405^m
Prosopis juliflora	110ⁿ	487^c	0.061^bcd	597	435^l
Rhus natalensis	172^k	438^kl	0.060^bcd	610^j	467^j
SEM	5.31	1.07	0.010	0.980	0.980
Species	0.001	0.001	NS	0.001	0.001
Season	0.001	0.001	0.050	0.001	0.001
Species * season	NS	0.001	NS	NS	NS
a = soluble fraction that rapidly washed out; b = insoluble but potential degradable by micro-organism; c = degradation rate; PD = potential degradable; ED = effective degradability at an out flow rate of 0.04h ^-1; NS = non-significant; Means with different letters within column are significantly different at P≤0.05

Seasonal variations in chemical composition, in vitro digestibility and ruminal degradation of browse species in the Rift Valley of Ethiopia

Ahmed Hassen1, Zewdu Kelkay Tessema and Adugna Tolera2

Abstract

Introduction

Materials and methods

Description of the study area

Sample collection and preparation

Chemical analyses and IVDMD determination

In sacco DM degradability

Results

Chemical composition and IVDMD of browse species

Total phenol and tannin contents of browse species

In sacco DMD of browse species

Discussion

Chemical composition and IVDMD values of browse species

Total phenol and tannin contents

In sacco DM degradability

Conclusions

Acknowledgement

References

Ahmed Hassen¹, Zewdu Kelkay Tessema and Adugna Tolera²