Review Article | Open Access
Minyahel Tilahun, Melesse Etifu, Tesfaye Shewage, "Plant Diversity and Ethnoveterinary Practices of Ethiopia: A Systematic Review", Evidence-Based Complementary and Alternative Medicine, vol. 2019, Article ID 5276824, 9 pages, 2019. https://doi.org/10.1155/2019/5276824
Plant Diversity and Ethnoveterinary Practices of Ethiopia: A Systematic Review
The systematic review was conducted on Ethnoveterinary Medicinal (EVM) plants from the two (integrated and pastoral) majorly known livestock production systems (LPS) of Ethiopia. A total of 48 documents pertinent to EVM significance were assessed from different sources using Google search engine and local university websites. Search outputs were screened using the developed inclusion criteria, and only 26 documents were selected. Descriptive analysis measures, Document Consensus Factor (DCF), and rank of the collected data were analysed using SPSS version 20 and Microsoft Excel. The result showed that females (33%), being below 40 years of age (27%), and educational level of above college (1%) healers participation was not significance. A total of 645 EVM plant species (from 133 families) were identified. Only 22 (16.54%) plant families were represented by one species. Leaf (47.8%) was the major plant part used to prepare remedies. The major administration route was oral route (58.2%). Blackleg 43 (0.188), diarrhea 25 (0.110), and wound 18 (0.079) were the most commonly treated livestock ailments. Solanaceae and Fabaceae were the frequently utilized EVM plant families in integrated and pastoral LPS, respectively. Croton macrostachyus (Bisana) and Solanum incanum (Embuay) were the most widely applied EVM plant species in integrated and pastoral LPS, respectively. Pastoral LPS were using higher number of specific EVM plants (DCF>0.5) compared to integrated LPS. Less than 40% (n< 10) of the collected documents were dealing with measurability and risk of toxicity, giving emphasis to indigenous plant and constraints of EVM plants use.
In most African countries, traditional medicine has been bonded to people and animal health planning for centuries, and it has undergone a major revival for generations . Ethiopia history of medicinal practice has long been recognized both in human and in livestock ailments treatment . Although the livestock sector of Ethiopia has been estimated to contribute 19% of agricultural production by value, many hindering factors are presumed to be responsible for low livestock productivity and death of livestock . Livestock ailment is the awful constraint which contributes to the death of about 8–10% of the cattle, 14–16% of the sheep, and 11–13% of the goat population .
Over 6,600 higher plant species are found in Ethiopia of which 22 are threatened . About 30% of botanical medicinal preparations in Africa are probably effective . EVM involves solid amalgamation of dynamic herbal known-how and ancestral experience . It has particular importance in areas where modern veterinary services are absent, irregular, and/or expensive . EVM has much to offer and can be a cheap and readily available alternative compared to costly imported drugs . Traditional herbal knowledge has also an impact on the development of modern medicine .
Although every community has its own particular approach to health and disease even at the level of ethno-pathogenic perceptions of diseases and therapeutic behaviour, limited documents have been involved in multiethnolinguistic communities of Ethiopia. To overcome this, the very concept of systematic and scientific documentation of such knowledge is very important . Hence, this document is designed to systematically review the EVM plants diversity and their use to treat livestock ailments in different LPS of Ethiopia.
2. Materials and Methods
2.1. Techniques of Data Collection
This systematic review was conducted between June 2017 and February 2018. The ecological zones used for this systematic review referred to agroclimatic zones classification of Ethiopia by Tessema Bekele . Even though the agroclimatic zones are seventeen, only six, i.e., Alpine Wurch (>3700 masl), Wurch (>3200-3700 masl), Dega (>2300- 3200 masl), and Weina Dega (>1500-2300 masl), which reserve integrated LPS, and Kolla (500-1500 masl) and Bereha (< 500 masl) which reserve pastoral LPS were used to classify the agroclimatic zones into two (i.e., integrated and pastoral) broad LPS categories of Ethiopia based on the available and accessed document. Furthermore, this systematic review emphasized solely the importance of EVM on the two major LPS of Ethiopia.
2.2. Sources and Screening Criteria
A web-based systematic research literature search strategy was employed using keywords/ phrases “Ethno veterinary medicinal plant of Ethiopia”. Published and unpublished sources were accessed using Google search engine, local university websites, international scientific databases including “Pub Med”, “Science direct”, “Web of Science”, “Google scholar”, and “African Journals Online (AJOL)”.
Two stages were followed to screen out the search outputs from websites. First, the title and abstract of the identified documents were overviewed. Then, appropriate documents for the systematic review were downloaded/collected and critically inspected for fulfilling the inclusion criteria.
2.3. Inclusion Criteria and Exclusion Criteria
Although many authors/documents provided multiple years of data, this systematic review focused only most recent years (i.e., the year 2005 onwards) of EVM documents. This considered the transition of vegetation cover and availability of plant species on the study areas, and further experimental and empirical study on this issue might require use of availability plant families and species on the study areas. Availability of necessary detailed data (i.e., plant part use, plant habit, scientific name, source, etc.) which describe the botanical description of those EVM plants to treat livestock ailments was also taken as a filtering factor.
Review articles, historical documents, or experimental studies were excluded bearing in mind their less rendering nature of originality, scarcity of descriptive and analyzable data, and difficulty for recommendation. Documents which focus on human related traditional medicine, documents which lack information about the study areas, and documents which did not properly describe informant’s involvement and scientific name of plants were the other exclusion criteria. Nevertheless, the excluded documents were used in discussion part of this systematic review. Ultimately, based on the specified inclusion criteria, a total of 26 documents, i.e., 10 from integrated and 16 from pastoral LPS, were selected and used for this systematic review.
2.4. Data Retrieval
Family name of specific plant and misspelled scientific names were retrieved from Natural Database for Africa (NDA), Version I 2.0 . In addition, documents which lack specific geographic locations/localities/districts information were retrieved through direct web (Google) searching.
2.5. Documents Consensus Factor (DCF)
The level of homogeneity within information provided by different informants/documents was calculated by the Informants’ Consensus Factor (ICF) . However, this systematic review modified the concept of ICF to Documents Consensus Factor (DCF) considering selected documents as an informant use of ICF, with the rest of the formula left as it is. where Nur is number of use reports from documents for a particular plant use category and Nt is number of plant taxa or species used to treat livestock ailments from all the included documents. DCF value range was between 0 and 1, where ‘1’ indicates the highest level of document consent and ‘0’ indicates the lowest document consent. Generally, DCF value of above 0.5 indicates majority of the documents agree up on the specific plants use in treating livestock ailment.
2.6. Data Analysis
This systematic review employed descriptive and explanatory analysis. Mean and Standard Error of Mean (SEM) were performed with SPSS version 20.0, and Microsoft Excel was used to compare the DCF values of specific plant species which are used to treat livestock ailments among the documents, and to calculate indexes and ranks of livestock ailments treated by EVM plants on different LPS of Ethiopia.
3. Results and Discussion
3.1. Characteristics of the Reviewed Documents on EVM Use
Table 1 presents characteristics of the documents used in the systematic review. The documents used for this systematic review were characterized based on the developed inclusion criteria that only focused on EVM knowledge. One can predict the practice of EVM based on the number of livestock and the vegetation cover of specific area. Almost all ecological zones, ethnic groups and communities have been identified in trusting EVM without the limitations of the availability and accessibility of infrastructure. The systematic review revealed that 645 different EVM plant species from 133 families were identified from the included documents.
Note that numbers written under square brackets are references/documents used for the analysis of the systematic review.
The systematic review showed that, of the informant and healers, only 33 % were females. This result is in line with  which stated the younger generation in Ethiopia is increasingly losing interest in learning about the medicinal herbs. The educational levels of all the informants or healers of the pastoral LPS were below college. The systematic review revealed that measure of reliability 13(43.3%), measurability 3(10%), toxicity risk assessment 1 (3.33%), and stressing constraints 4 (13.3%) were not given due stress on the included documents. In pastoral LPS, the proportion of plant families which were represented by more than one plant species 61 (67.8%) was higher than the integrated LPS 53 (45%). In contrast to this systematic review,  reports that only 31% of integrated LPS plant families are represented by more than one plant species. Respondent’s or healer’s knowledge of identifying the EVM botanical families and their corresponding species might bring variability in the number of identified plant species.
3.2. EVM Sources and Plant Habits
Table 2 describes the EVM plants sources and habits. Source of EVM plants for both LPS were majorly from wild sources (80.57±2.25). The systematic review revealed that market was not used as source of EVM plant for pastoral LPS. Herbs both from integrated and from pastoral LPS showed higher average proportion of 32.05±10.24 and 31.19±23.52, respectively. Pastoral LPS used lower average proportion (18.92±15.93) of trees as compared to integrated LPS (31.82±11.03). This might be due to plant reservation capacity of specific ecologies. Some EVM plants are available only in certain seasons of the year. This might often hinder the application of traditional medicine. Moreover, some of the preparations use mixtures of plants which are difficult to find at specific season .
Note that mixed sources represent any of i.e. wild, cultivated and market can be the sources of EVM plant (only for integrated LPS); plant habit means ability of plants to adapt to its evolving environment.
3.3. Routes of EVM Administration
Table 3 presents EVM administration routes in integrated and pastoral LPS of Ethiopia. Oral route of administration (50.11±21.60) was the major route in both LPS. Topical and nasal routes were the second and third routes of administration in both LPS and at country level.
The proportion of dermal (8.11± 2.8) and nasal (13.39± 3.8) routes of administrations in pastoral LPS were much higher than integrated (2.93± 2.07; 5.74± 1.84) LPS. This might be due to the fact that prevalence rate of dermal and respiratory ailments in pastoral LPS is higher than other livestock ailments. The result of this systematic review is in line with [13–16, 18, 30].
3.4. Plant Part Used for Treatment
Different plant parts used in treating livestock ailments are described in Figures 1(a) and 1(b). Leaf was the major plant part used to treat livestock ailments both in integrated (46.89%) and pastoral (45.59%) LPS of Ethiopia. The second and third majorly used plant parts both in integrated (21.94%; 6.53%) and pastoral (23.81%; 7.66%) LPS were root and seeds/fruit, respectively. The finding of this systematic review is in line with [13, 16].
(a) Integrated LPS
(b) Pastoral LPS
3.5. Major Livestock Ailments Treated and DCF of EVM from the Selected Documents
Frequently treated livestock ailments and DCF value of major EVM plant species are presented in Table 4. Black leg was indexed first 43 (0.188) among the different documented ailments. Tree species like Justice schimperiana, Allium sativum, and Lapidum sativum were the frequently documented plant species used to treat blackleg. Other livestock ailments, i.e., diarrhea 25 (0.110), wound 18 (0.079), and bloat 17 (0.073), were ranked second, third, and fourth, respectively. Most ailments treated in pastoral LPS showed higher DCF value (i.e., DCF> 0.5) than integrated LPS for similar ailments. This might be due to the fact that availability of different EVM plants in integrated LPS could let healers/respondents depend on various EVM plants rather than specific EVM plant. This result is supported by the works [9, 12, 13, 16, 20, 22, 34] which indicates different DCF value of livestock ailment from the selected documents reveal that less than six plants are specifically used to treat specific livestock ailment from integrated LPS. The majorly treated livestock ailments of this study were supported by number of documents [19, 20, 29, 34]. However, this result is in contrast with [18, 27] which indicate the majorly treated livestock ailments are diarrhea and wound rather than black leg. The in agreement might be due to the prevalence rate of most livestock ailments from different agroecology oblige healers and respondents to focus on frequently occurring ailment with long years of experience in treatment.
Note that plant species name under prentices represent Amharic language.
3.6. Frequently Utilized EVM Plants
Table 5 presents the frequently utilized EVM plants in pastoral and integrated LPS of Ethiopia. The frequently utilized EVM plant family was Fabaceae 45 (8.11%) and Solanaceae 44 (7.94%) for pastoral and integrated LPS, respectively. Fabaceae 72(11.16%) was ranked first at country level. Croton macrostachyus (Bisana) 15(21.43%) was the frequently utilized plant species to treat livestock ailments of the country. However, its contribution was higher in integrated 7(70%) than pastoral 8(50%) LPS of Ethiopia. Solanum incanum (Embuay) 9(75%) was the principal EVM plant species in pastoral LPS of Ethiopia. The result of this systematic review is supported by [14, 16, 30]. Other studies [13, 16, 19, 20, 22, 26, 27] report that the frequently utilized plant families and species are in contrast to the finding of this systematic review. Agroecological factors can determine the type and abundance of EVM plants that can grow in an area . Moreover, the utilization frequency of those effective EVM plant species might coincide with the presence of bioactive ingredients against livestock ailments. The frequency of using such EVM plant families and species might be correlated to the prevalence rate of some livestock ailments such as ticks and flies in pastoral LPs demand specific EVM plant species like Calpurnia aurea (Hits awuts) (Table 4). A common Amharic proverb ‘Gizawa eyale edejishi lije motebign tiyalesh’ acknowledges the ubiquitous significance of Withania somnifera and its astonishing uses against evil eye and sudden death. Furthermore, the proverb also indicates communities’ faith on medicinal plants healing power even to the worst extreme of life which is death.
Note that different EVM plant species vernacular names are from different ethnic groups of Ethiopia. “Am” represents Ethiopian national language which is Amharic language; “n” represents the number of plant species on each LPS.
The present systematic review revealed that Ethiopia has rich EVM plant diversity, i.e., 645 different plant species from 133 families. Among the EVM plant families, Solanacea and Fabaceae are the major EVM plant families in integrated and pastoral LPS, respectively. Croton macrostachyus (Bisana) and Solanum incanum (Embuay) are the frequently utilized EVM plant species in integrated and pastoral LPS of Ethiopia, respectively. Black leg (Aba gorba), diarrhea (Tekimat), wound (Kusil), and bloat (Yehod meketet) are the four mostly treated livestock ailments. Higher number of livestock ailments from pastoral LPS has a DCF value of greater than 0.5 as compared to integrated LPS. Women and younger generation contribution and involvement in the preparation and knowledge development of ethnic medicine are very insignificant. Moreover, the majority of the documents lack information about herbal toxic effect, dosage, measurability and conservation. Revealing the appropriate dosage in divergent preparation and use patterns of herbal remedies among multiethnolinguistic communities, as well as associated toxicity risks and countermeasures, generally demand deeper and exhaustive investigations. Therefore, sustainable development and exploitation strategy which focus on protecting the endangered medicinal plants necessitate coordinated multidisciplinary research programs that give due credit to create responsible traditional practitioners and commercial investors.
Conflicts of Interest
The authors declare that there are no conflicts of interest regarding the publication of this paper.
- M. A. Caudell, M. B. Quinlan, R. J. Quinlan, and D. R. Call, “Medical pluralism and livestock health: ethnomedical and biomedical veterinary knowledge among East African agropastoralists,” Journal of Ethnobiology and Ethnomedicine, vol. 13, no. 1, article no. 7, 2017.
- R. Pankhurst and T. Pearson, “Remedius Prutkys 18th century account of Ethiopian taencides and other medicinal treatment,” Ethiopian Medical Journal, vol. 10, pp. 3–6, 1972.
- N. Dharani, A. Yenesew, E. Aynekulu, B. Tuei, and R. Jamnadass, “Traditional ethno-veterinary medicine in East Africa: a manual on the use of medicinal plants,” in The World Agro forestry Centre (ICRAF), I. K. Dawson, Ed., Nairobi, Kenya, 2015.
- K. Behailu, “Assessment of the quality of veterinary education and career opportunities for veterinarians in Ethiopia,” in Proceedings of the 25th Annual Conference of the Ethiopian veterinary Association, pp. 1–38, Held at the United Nations Conference Centre, 2011.
- T. A. Bekele, “Useful trees of Ethiopia: identification, propagation and management in 17 agro ecological zones,” Nairobi: RELMA in ICRAF Project, p. 552, 2007.
- F. Fullas, “Ethiopian Medicinal Plants in Veterinary Healthcare: A Mini Review,” Ethiopian e-Journal for Research and Innovation Foresight, vol. 2, pp. 48–58, 2010.
- K. Mesfin, G. Tekle, and T. Tesfaye, “Ethno botanical study of traditional Medicinal Plants used by indigenous people of Gemad District,” Journal of Medicinal Plants Studies, vol. 1, no. 32, p. 37, 2013.
- N. J. Toyang, J. Wanyama, M. N. wanyakpa, and S. Django, “Ethnovetrinary medicine. A practical approach to the treatment of cattle disease in sub-saharan Africa,” Agrodok, vol. 44, article no. 88, 2007.
- T. Sori, M. Bekana, G. Adugna, and E. Kelbessa, “Medicinal plants in the ethno veterinary practices of Borana pastoralists, Southern Ethiopia,” The International Journal of Applied Research in Veterinary Medicine, vol. 2, pp. 220–225, 2004.
- R. R. N Alves and I. L. Rosa, “Why study the use of animal products in traditional medicines?” Journal of Ethnobiology and Ethnomedicine, pp. 1–5, 2005.
- U. Lohani, K. Rajbhandari, and K. Shakuntala, “Need for systematic ethnozoological studies in the conservation of ancient knowledge systems of Nepal - A review,” Indian Journal of Traditional Knowledge, vol. 7, no. 4, pp. 634–637, 2008.
- Y. Tekle, “Medicinal plants in the ethno veterinary practices of bensa woreda, Southern Ethiopia,” Open Access Library Journal, vol. 2, Article ID e1258, 2015.
- M. M. Mekonnen, F. Tessema, M. Yilma, T. Getachew, and M. Asrat, “Documentation of Ethno Veterinary Practices in Selected Sites of Wolaita and Dawuro Zones, Ethiopia,” Global Journal of Science Frontier Research: Agriculture and Veterinary, vol. 16, no. 5, pp. 2249–2626, 2016.
- G. R. Eshetu, T. A. Dejene, L. B. Telila, and D. F. Bekele, “Ethnoveterinary medicinal plants: preparation and application methods by traditional healers in selected districts of southern Ethiopia,” Veterinary World, vol. 8, no. 5, pp. 674–684, 2015.
- C. Mohammed, D. Abera, M. Woyessa, and T. Birhanu, “Survey of ethno-veterinary medicinal plants in Melkabello District,Eastern Harerghe Zone, Eastern Ethiopia. Ethiopian,” Veterinary Journal, vol. 20, no. 2, pp. 1–15, 2016.
- Y. Tekle, “Study on Ethno-veterinary Practices in Amaro special District Southern Ethiopia,” Medicinal and Aromatic Plants, vol. 4, no. 2, article no 186, 2014.
- T. Firaol, W. T. Erfa, E. Kebede, G. Dabessa, and M. Sorsa, “Ethno knowledge of plants used in veterinary practices in Dabo Hana District,” Journal of Medicinal Plant Research, vol. 7, no. 40, pp. 2960–2971, 2013.
- N. Mekonnen and E. Abebe, “Ethnobotanical knowledge and practices of traditional healers in Harar, Haramaya, Bati and Garamuleta, Eastern Ethiopia,” Ethiopian Veterinary Journal, vol. 21, no. 2, pp. 40–61, 2017.
- Y. Yigezu, D. B. Haile, and W. Y. Ayen, “Ethnoveterinary medicines in four districts of jimma zone, Ethiopia: cross sectional survey for plant species and mode of use,” BMC Veterinary Research, vol. 10, article 76, 2014.
- E. Lulekal, Z. Asfaw, E. Kelbessa, and P. Van Damme, “Ethnoveterinary plants of Ankober District, North Shewa Zone, Amhara Region, Ethiopia,” Journal of Ethnobiology and Ethnomedicine, vol. 10, no. 1, article no. 21, 2014.
- K. Giday, L. Lenaerts, K. Gebrehiwot, G. Yirga, B. Verbist, and B. Muys, “Ethnobotanical study of medicinal plants from degraded dry afromontane forest in northern Ethiopia: Species, uses and conservation challenges,” Journal of Herbal Medicine, vol. 6, no. 2, pp. 96–104, 2016.
- M. Giday and T. Teklehaymanot, “Ethnobotanical study of plants used in management of livestock health problems by Afar people of Ada'ar District, Afar Regional State, Ethiopia,” Journal of Ethnobiology and Ethnomedicine, vol. 9, no. 1, article no. 8, 2013.
- G. Yirga, M. Teferi, G. Gidey, and S. Zerabruk, “An ethnoveterinary survey of medicinal plants used to treat livestock diseases in Seharti-Samre district, northern Ethiopia,” African Journal of Plant Science, vol. 6, no. 3, pp. 113–119, 2012.
- F. Abraha, Indiginous livestock husbandary and Ethno veterinary practices in Endamohoni district of tigray region Ethiopia (Msc thesis), Hawassa University, Hawassa, Ethiopia, 2016.
- T. Teklehaymanot, “An ethnobotanical survey of medicinal and edible plants of Yalo Woreda in Afar regional state, Ethiopia,” Journal of Ethnobiology and Ethnomedicine, vol. 13, article no. 40, no. 1, 2017.
- K. Tolossa, E. Debela, S. Athanasiadou, A. Tolera, G. Ganga, and J. G. M. Houdijk, “Ethno-medicinal study of plants used for treatment of human and livestock ailments by traditional healers in South Omo, Southern Ethiopia,” Journal of Ethnobiology and Ethnomedicine, vol. 9, no. 1, article no. 32, 2013.
- T. Feyera, E. Mekonnen, B. U. Wakayo, and S. Assefa, “Botanical ethnoveterinary therapies used by agro-pastoralists of Fafan zone, Eastern Ethiopia,” BMC Veterinary Research, vol. 13, article no. 232, 2017.
- M. Mengistu, E. Kebede, and B. Serda, “Ethnobotanical Knowledge of Pastoral Community for Treating Livestock Diseases in Shinle Zone, Somali Regional State, Eastern Ethiopia,” Journal of Veterinary Science & Technology, vol. 8, no. 5, 2017.
- Y. Tekle, “An ethno-veterinary botanical survey of medicinal plants in Kochore district of Gedeo Zone, Southern Nations Nationalities and Peoples Regional State (SNNPRs, Ethiopia),” Journal of Scientific and Innovative Research, vol. 3, no. 4, pp. 433–445, 2014.
- G. Kitata, D. Abdeta, and M. Amante, “Ethno-knowledge of plants used in veterinary practices in Midakegn district, west Showa of Oromia region, Ethiopia,” Journal of Medicinal Plants Studies, vol. 5, no. 5, pp. 282–288, 2017.
- M. Giday, Z. Asfaw, Z. Woldu, and T. Teklehaymanot, “Medicinal plant knowledge of the Bench ethnic group of Ethiopia: an ethnobotanical investigation,” Journal of Ethnobiology and Ethnomedicine, vol. 5, article 34, 2009.
- A. Kebede, S. Ayalew, A. Mesfin, and G. Mulualem, “An Ethno-veterinary Study of Medicinal Plants Used for the Management of Livestock Ailments in Selected kebeles of Dire Dawa Administration, Eastern Ethiopia,” Journal of Plant Sciences, vol. 5, no. 1, pp. 34–42, 2017.
- E. Amenu, Use and management of medicinal plants by indigenous people of Ejaji area (chelya woreda) West Shoa, Ethiopia: an Ethnobotanical approach (MSc Thesis), Addis Ababa, Ethiopia, June 2007.
- B. Kidane, L. J. G. Van Der Maesen, T. Van Andel, and Z. Asfaw, “Ethnoveterinary medicinal plants used by the Maale and Ari ethnic communities in southern Ethiopia,” Journal of Ethnopharmacology, vol. 153, no. 1, pp. 274–282, 2014.
- A. Assefa and A. Bahiru, “Ethnoveterinary botanical survey of medicinal plants in Abergelle, Sekota and Lalibela districts of Amhara region, Northern Ethiopia,” Journal of Ethnopharmacology, vol. 213, pp. 340–349, 2018.
- G. Gebrezgabiher, S. Kalayou, and S. Sahle, “An ethno-veterinary survey of medicinal plants in woredas of Tigray region,” International Journal of Biodiversity and Conservation, vol. 5, pp. 89–97, 2013.
- D. Ermias, Natural data base for Africa (NDA), Edition: Version 2.0; Date of release August 2011, 2011, http://aritiherbal.com/.
- R. T. Trotter and M. H. Logan, “Informant census: A new approach for identifying potentially effective medicinal plants,” in Plants in Indigenous Medicine And Diet, N. L. Etkin, Ed., pp. 91–112, Bedford Hill, Redgrave, NY, USA, 1986.
- E. d'Avigdor, H. Wohlmuth, Z. Asfaw, and T. Awas, “The current status of knowledge of herbal medicine and medicinal plants in Fiche, Ethiopia,” Journal of Ethnobiology and Ethnomedicine, vol. 10, no. 38, 2014.
- T. Mesfin and T. Obsa, “Ethiopian traditional veterinary practises and their possible contribution to animal production and management,” Revue Scientifique et Technique de l'OIE, vol. 13, no. 2, pp. 417–424, 1994.
Copyright © 2019 Minyahel Tilahun et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.