Utilization and nutritive value of sesame (Sesamum indicum L.) straw as feed for livestock in the North western lowlands of Ethiopia

Teferi Aregawi, Getachew Animut* and Habtremariam Kassa*

Humera Agricultural Research Center, P.O.Box 65, Humera, Ethiopia
teferia2005@yahoo.com
* School of Animal and Range Sciences, Haramaya University, P.O.Box 138, Dire Dawa, Ethiopia

Abstract

The handling, utilization, feeding practices of sesame straw (SS) and constraints limiting its use in two districts, namely Kafta Humera and Metema of the Northwestern lowlands of Ethiopia were assessed by interviewing 120 households stratified into three strata (poor, middle and better off) based on wealth status. For evaluating the nutritional values of SS, samples from three sesame cultivars (Hirhir, Adi and Bawnji) and three straw morphological fractions (whole straw, stem and capsule) were considered.
 

The annual estimated SS yield was 142,369 tonnes in Kafta Humera and 27,605 tonnes in Metema. The amount of SS used as animal feed in Kafta Humera district was about 16.4% of the SS produced, and was almost three fold to that used in Metema district. Based on wealth categories, the middle and poor households utilized SS for economical purposes such as feed, as mulch and as source of income more than the better off. Lack of awareness was the major constraint by all respondents in Metema and by 59% of the respondents in Kafta Humera noted as limiting factor for the use of SS as animal feed. The crude protein (CP) content was greater in the capsule (5.44%) than in the stem (3.56%), and that of the neutral detergent fiber (NDF) was lower in the capsule (61%) than in the stem (77%) fraction, while value for the whole straw was intermediate. In vitro organic matter digestibility (IVOMD) ranged from 32% for stem to 50% for capsule. IVOMD differ among cultivars (P < 0.05) and was 41.7, 39.1 and 38.5% for Hirhir, Bawnji and Adi, respectively. In general, SS is low in CP and IVOMD, but high in cell wall fiber content. Therefore, efficient utilization of SS in the study area necessitate for designing appropriate strategies to enhance the feeding value of the straw, along with the creation of awareness about the potential of the resource as feed.

Key words: collection and storage, constraints, feeding system, processing, treatment

Introduction

Inadequate feed supplies stands as the most important constraint facing livestock production in developing countries. Crop residues, the fibrous by-products from the cultivation of cereals, pulses, oil crops, roots and tubers, represent an important feed resource for livestock production in developing countries. Crop residues provide fodder at low cost since they are by-products of the existing crop production activities. Nonetheless, there is a perception that the potential of crop residues as livestock feed has not been fully exploited, given the rapid expansion in commercial farming such as sesame seed production that has taken place in recent years in developing countries like Ethiopia.

Ethiopia has an attractive portfolio of high value sesame seed production for export market. In the year 2010, the country was reported as the third largest global exporter of sesame next to Nigeria and India (ITC 2011). The major sesame growing areas in Ethiopia are located in the Northwestern lowlands. Area allocated to sesame production in Ethiopia both at regional and national level has been increasing from time to time. Time series data indicated that the area coverage by sesame increased from 34,193 ha in 2003/04 to 166,960 ha in 2008/09 cropping season in Northwestern lowlands of Ethiopia (Kafta Humera and Metema districts in particular) (CSA 2009). Such a rapid expansion in area coverage for sesame production severely limited access to grazing land. On the other hand, the expansion of sesame cropping has raised the importance of sesame straw as animal feed. However, limited research has been undertaken concerning the available volume and nutritional quality of sesame straw. Little is known about sesame straw in terms of the level of use, feeding system and methods that could be used to improve the value of the straw as livestock feed. With the increasing need to explore alternative and cost effective feedstuffs, research into the use of sesame straw as livestock feed will have an important implication for livestock production in an era where population pressure is seriously reducing grazing lands that used to provide most of the livestock feed in Ethiopia. Therefore, this study was designed to assess and document current views and practices in the management and use of sesame straw, and to evaluate the nutritional value of the straw as feed for livestock.

Materials and methods

Study sites

The study was conducted in Kafta Humera and Metema districts found in the Northwestern lowlands of Ethiopia. The districts are known for their sesame production. Kafta Humera is located between 13o14’ to 14o27’ N latitude and 36o27’ to 37o32’E longitude, with an average altitude of 568 meters above sea level (masl). The maximum temperature varies between 42 oC in April and 33 oC in August, while the minimum temperature ranges from 22.2 oC in May to 17.5 oC in July. The mean annual temperature is 26 oC and the average annual rainfall is 448 mm (MOA 1998). Metema district is located between 11o56’ to 13o45’ N latitude and 35o11’ to 35o50’E longitude, with an altitude ranging 550 to 1068 masl. The daily temperature becomes high during the month of March to May and it can reach 43oC. The mean annual temperature is 25 oC and the annual rainfall of Metema district ranges 850 to 1,100 mm (ILRI 2005). In both districts, livestock production is an integral part of the agricultural system.

Sampling of respondents

A two stage sampling method was employed. Out of all kebeles  (Kebele is the lowest administrative unit of Ethiopia) in the two districts six kebeles (three from each district) were selected purposively to encompass the dominantly sesame producing kebeles. In the second stage, the households in each of the selected kebeles were stratified into three strata (poor, middle and better off) based on wealth status. A total of 120 (60 from each district) households were selected for the primary data collection. In each district equal number of households from the three wealth categories were used for the survey.

The sampling frame was identified using wealth ranking criteria set by the community. Possession of livestock, cultivated land size, number of farming oxen and type of house owned were the most important criteria used for wealth ranking in the study area. The group which was used to establish the relative wealth position of the households in the community was composed of key informants in each Kebele (men, women, elders, and youth) based on the assumption that community members have a good sense of who among them is well off. According to the criteria set by the wealth ranking group, farmers who have greater than 10 cows, greater than 10 ha of cultivated land size, more than two pairs of oxen and house with corrugated iron or grass house with partition were considered as better off farmers. Farmers who have 4 to 10 cows, 3 to 10 ha of cultivated land, 1 to 2 pairs of farming oxen and house with corrugated iron or grass house with partition were considered as medium farmers. Farmers who have less or equal to 3 cows, less or equal to 2 ha of cultivated land, less or equal to 1 farming oxen and grass house were considered as poor farmers.

Survey data collection

Questionnaire was prepared and pretested, and structured questionnaire was developed to collect the survey data. Primary data on sesame straw collection, storage and processing, utilization of the straw for various purposes including for feed, the feeding practices of sesame straw, reasons for not collecting sesame straw for feeding, feeding priorities of the straw for livestock, and constraints limiting its use as feed were collected from the respondents using both informal surveys (individual interviews, group discussions, field level observations) and structured questionnaire.

The quantity of dry matter (DM) of sesame crop residue was estimated by converting grain yield to fibrous residues using multiplier of 1.2 developed for oil crops with a utilization factor of about 90% (FAO 1987). Farmer households were interviewed to indicate their sesame grain yield in the year 2011 cropping season, and this value was used to estimate sesame straw yield per hectare from grain yield per hectare. Respondents were also interviewed to estimate the quantity of sesame straw utilized for different purposes.

Sampling of sesame straw for nutritional evaluation

To evaluate the nutritional value of sesame straw through chemical analysis and in vitro OM digestibility, samples from three sesame crop cultivars (Hirhir, Adi and Bawnji) which are widely cultivated in the area for export market were collected. The whole straw (Whole straw represents both stem and capsule bulked together, capsule refers to the pod or the part of the plant bearing seeds, and stem refers to the part of the crop residue without the capsules and leaves), straw morphological fractions, namely stem and capsule were collected for nutritional evaluation. Sesame leaves are all defoliated at maturity before harvest and as such were not considered in nutritional evaluation. The samples were collected from three different locations. Thus, the nutritional evaluation of sesame straw employed three straw fractions (stem, capsule and whole straw) and three cultivars (Hirhir, Adi and Bawnji) in a 3 x 3 factorial arrangement of treatments, each treatment being replicated three times across the three locations. Samples of the three straw fractions of the cultivars were separately taken from the field immediately after crop harvest.

Laboratory analysis

All sesame straw samples were analyzed for DM, ash, and nitrogen (N) using the procedure of 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 determined following the procedure of Van Soest and Robertson (1985). In vitro organic matter digestibility (IVOMD) was determined by the two-stage method of Tilley and Terry (1963). Samples were incubated for 48 hours with rumen fluid and buffer followed by another 48 hour digestion with pepsin and HCl, and the residue was ashed in a muffle furnace at 550 OC for 5 hour. Rumen fluid was obtained from rumen fistulated Boran x Holstein Frisian steers kept at maintenance dietary condition with diets containing hay supplemented daily with 4 kg of concentrate mixture comprised of 74, 25 and 1% wheat bran, noug seed cake and salt, respectively.

Statistical analysis

Descriptive statistics was employed to explain the survey data, and statistical package for social sciences (SPSS 1999) was used to analyze the data. T-test and Chi-square statistics were employed to determine mean and percentage differences between the districts and among wealth groups. Data for nutritional evaluation parameters was subjected to analysis of variance (ANOVA) using the General Linear Model (GLM) procedure of statistical analysis system (SAS 2002) with the model consisting of straw fraction, cultivars and their interaction. However, differences among interaction means were small and thus only main effect means are reported.  When analysis of variance (ANOVA) declare significant difference among treatment means, mean comparison was carried out using least significant difference (LSD).

Results and discussion

Use of sesame straw

Sesame straw production in Kafta Humera and Metema districts was 0.563 and 0.562 ton/ha, respectively (Table 1). The current estimate for sesame straw production appeared to be slightly lower than earlier estimate for other cereal straws with straw production of 0.75, 0.98, 0.96, 0.65 and 0.78 ton/ha for teff, barley, wheat, field peas and haricot bean, respectively (CSA 1984). Given an estimated area used for sesame production in Kafta Humera and Metema districts in the year 2011/12 production season to be 253,100 (KHOARD 2012) and 49,145 ha (MOARD 2012), respectively, a total of 142,369 and 27,605 ton of sesame straw is produced annually in the two districts, respectively. With an approximate feed intake of 1.7% body weight of the animals for crop residues (Devendra 1985) a total of 93,052 and 18,043 tropical livestock units (TLU) can be maintained annually in Kafta Humera and Metema districts, respectively, using sesame straw. This estimate indicates the potential of sesame straw as feed for livestock.

The economic role of sesame straw appeared to be greater in Kafta Humera than Metema (Table 1) as more sesame straw is being used as animal feed and sold in Kafta Humera district. This situation could be associated with availability of alternative feed resources in Metema (Table 3). Comparison of the three wealth categories for the utilization of sesame straw (Table 1) indicated that the poor and the middle households utilized the straw for economical purposes such as feed, as mulch and as a source of income more than the better off categories.

Sesame straw not utilized for economical purposes is generally burned, which accounts for about 67.7% and 75.3% of the sesame straw produced in Kafta Humera and Metema districts, respectively (Table 1). According to the respondents, the main reason for burning the straw is to eradicate insect pests particularly sesame seed bug, the predominant bug species attacking sesame in the study area. Moreover, burning of the straw serves as a quick and labor saving strategy for straw disposal. This observation is in agreement with the findings of Ping et al (2010) in Taiwan who noted the farmers’ response that burning rice stalks after harvest to be the best way to kill insect larvae as well as  to save the trouble of transporting and disposing the stalks. However, this constitutes not only loss in terms of considerable amount of organic nutrients that may serve as livestock feed, but also adds up to environmental damage through carbon released to the atmosphere.

Collection and storage

Most respondents do not practice collection and storing of sesame straw for future use in the study area (Table 2). Only the poor households undertake the storage practice in Metema district, while the medium and poor households undertake the practice more than the better offs in Kafta Humera district. Different reasons have been noted by respondents for not collecting and storing sesame straw (Table 3) and the main one was lack of awareness. In Metema, the presence of alternative feeds did not encourage farmers to collect and store the straw. Some of the middle and poor households indicated lack of transportation and the use of the straw for mulching as additional reasons for not collecting and storing sesame straw. Most of the better offs have large area of land ranging 10 to 3000 ha, and most of the land is located distant from home and was mentioned as a reason for not collecting sesame straw. Sesame is threshed in the field, and the utilization of the straw demands transporting the straw to homesteads where animals are kept or to use it latter in the dry season. In situations of lack of transportation less straw are collected and stored for animal feeding. Owen and Aboud (1988) also noted that the bulky nature of crop residues and lack of means of transportation to be among the factors that constrain the collection and hence greater use of straws and stovers as feed. Other reasons noted by respondents for not collecting and storing sesame straw include shortage of time, shortage of labor, less palatability of the straw and not possessing of animals.

Treatment of sesame straw

Physical and chemical treatment of crop residues has long been recognized as means of improving the feeding value of crop residues (Preston 1986; Sundstol and Owen 1984). Although to a variable degree, intake and/or digestibility of crop residues has been enhanced through treatment of crop residues such as chopping, soaking with water and chemical treatment (Lu et al 2005). Out of the respondents that feed sesame straw to livestock, though most respondents (57% in Kafta Humera and 97% in Metema) do not process the straw before feeding, others employed some kind of treatment. About 35% of the respondents in Kafta Humera used chopping, 5% soak the straw in water and 3% used chemical treatment. The 3% of respondents in Metema employ chopping. 

Use of sesame straw as feed and perceived constraints limiting its use

About 54% of the respondents in Kafta Humera district and 8% in Metema perceive sesame straw to have similar feeding value with other crop residues of the area, while 27% of the respondents in Kafta Humera and 7% in Metema believe that the straw is lower in quality than other crop residues. About 85% and 19% of the respondents in Metema and Kafta Humera, respectively, perceive that sesame straw cannot be used as livestock feed. However, 64% of the respondents in Kafta Humera and 3% in Metema use sesame straw as livestock feed. In Metema, diverse crops such as sesame, cotton, sorghum, maize, soybean, teff, rice, chick pea and groundnut are grown, and provide opportunity for the choice of other crop residues as feed. In Kafta Humera sesame, cotton and sorghum are widely grown.

There were constraints noted by respondents that limit the use of sesame straw as feed. Lack of awareness was a major one reported by all respondents in Metema and by 59% of the respondents in Kafta Humera. About 30% of respondents in Kafta Humera do not use the straw as feed since livestock are kept far from where the straw is available. Thickness or hardiness of the stem by 54% of the respondents and unavailability of leaves during harvest according to 33% of the respondents were perceived in the whole study area as additional reasons for not utilizing sesame straw as feed. All respondents indicated the capsule to be more preferred by the animals than the stem, and sesame straw to be used only during the dry seasons when feed is scarce.

Among respondents using sesame straw as feed, most (85%) in Kafta Humera versus few (20%) in Metema feed the straw alone. About 9% of the respondents in Kafta Humera practice mixing the straw with other feeds such as sesame hulls and sesame oil by-product sesame seed cake. Most in Metema (80%) against few (6%) in Kafta Humera allow their animals to graze the straw left in the field. In both districts there is open access to sesame straw in the field. This communal use of sesame straw could be due to low population densities and the prevalent communal herd management practices in the area. In Zimbabwe, Sibanda (1986) noted that most stovers were fed to animals in situ, while only some farmers harvest and store the residues for later use. According to Sibanda (1986), though free grazing on crop residues left in the fields allow farmers to use residues without incurring storage and processing costs, this method of feeding results in low utilization rates due to trampling and spoilage.

Different type of crop residues serve as livestock feed in the study area. Sesame straw is primarily used for feeding cattle, camel and sheep and is not fed much to equines and goats (Table 4). In Kafta Humera the preferred crop residue for calves, cattle, goat and donkey is sorghum stover, and for sheep and camel is sesame straw (Table 5). In Metema, teff straw is the preferred crop residue for calves and cattle, while sorghum stover is preferentially used to feed sheep, goat, donkey and camel. Sesame hulls, sesame oil by-product sesame seed cake (locally known as ‘Embaze’), noug seed cake and wheat bran are the availlable supplement feeds in Metema, while sesame hulls and sesame oil by-products sesame seed cake are important supplements in Kafta Humera district.

Chemical composition and in vitro organic matter digestibility

The nutritive value of the capsule in terms of chemical composition and IVOMD appeared to be relatively better than the stem fraction and that of the whole straw was intermediate (Table 6). On the other hand differences in the chemical composition of the three cultivars used in this study were small. But depending on the fiber content and IVDOM, the feeding value of the cultivars appeared to be in the order of Hirhir > Bawnji > Adi. Differences in IVOMD values among the morphological fractions and/or the three sesame cultivars in this study was consistent with the variation in the level of CP and cell wall fiber (Van Soest 1988; McDonald et al 1995).

There is limited data in literature concerning the nutritional quality of sesame straw. Asma and Mohamed (2009) noted 4.52 and 7.84% for CP and ash content of sesame straw, respectively comparable to the results of this study. Kamali (2007) on the other hand reported slightly higher CP (5.05%) and ash (9.87%), and lower NDF (57.6%) and ADF (42.9%) contents for sesame straw as compared to the values obtained in this study. The chemical composition of sesame straw appeared to be comparable with values noted for other crop residues in the same study districts. For instance, the CP content of sesame straw in this study was similar with the value of 4.3 and 4.2% noted for teff straw and millet stover, respectively, (Sisay 2006), but was higher than the 3.1% reported for sorghum stover (Sisay 2006). The ash content of whole straw obtained in the present study was similar with the values reported (7.4%) for maize (Adugna et al 1999), but was much higher than the 0.43% for maize reported by Diriba et al (2011). Sisay (2006) also reported ash content of 8.9%, 9.8% and 7.9% for teff straw, millet and sorghum stovers, respectively. The NDF content of sesame straw appeared to be comparable to the level in teff straw and sorghum stover (Sisay 2006).

In this study ten plant samples of sesame straw from each of the three cultivars were collected immediately after harvest to determine the average number of capsules per plant. The mean number of capsules per plant was 85, 61 and 47 for Hirhir, Bawnji, and Adi, respectively. Thus, differences in IVOMD among the three cultivars noted in this study may be a consequence of the number and/or the proportion of capsules in the whole sesame straw. Apparently, the number of capsules per plant is positively correlated with seed yield (Ghulam et al 2007) as the capsule is part of the plant which is bearing the seed. Therefore, attempts to develop high yielder cultivar of sesame might increase capsule yield and thus relatively enhance the nutritionally value of sesame straw. Differences among sesame cultivars in chemical composition and IVOMD observed in this study is consistent with that reported for different maize varieties (Adugna et al 1999; Diriba et al 2011).

Conclusion

• Sesame is a major crop widely cultivated in the study districts. As a result huge amount of sesame straw is obtained in the area. Although the level of utilization between the districts varies, the amount of sesame straw used as animal feed in the study area is generally low. Most of the straw is wasted mainly due to the lack of awareness about the resource as animal feed. Similar to other crop residues, sesame straw is generally low in nutritional value. Therefore, efficient utilization of sesame straw in the study area necessitate for designing appropriate strategies to enhance the feeding value of the straw, along with the creation of awareness about the potential of the resource as feed.

Acknowledgements

The authors are greatly indebted to the Rural Capacity Building Project (RCBP) through Ethiopian Institute of Agricultural Research (EIAR) for funding this research. Experts, extension workers and farmers who took part in the interview and group discussion are duly acknowledged.

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Received 15 February 2013; Accepted 13 June 2013; Published 1 July 2013

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