Chemical composition of major livestock feed resources in the medium and low agroecological zones in the mixed farming system of Haru District, Ethiopia.

The poor nutritional quality of feed resources is one of the major constraints to optimal livestock productivity in Ethiopia. In the current study area, there is lack of information on the chemical composition of major feed resources to quantify their nutritional quality for interventions. The aim of this study was to assess the chemical composition of livestock feed resources (natural pasture, crop residues, local liquor byproduct (atella) and indigenous fodder tree and shrub species) in the medium and low agroecological zones (AEZs) in the mixed farming system of Haru District, Ethiopia. The feed samples were analysed in dry matter basis for ash dry matter (DM), crude protein (CP), acid-detergent fiber (ADF), neutral-detergent fiber (NDF) and ether extractor (EE)). The results revealed that nutrient content of feeds showed variation between the two AEZs. The overall mean DM, Ash, NDF, ADF, EE, and CP content of natural grass species ranged from 91.40 ± 0.84-92.26 ± 0.55 %, 6.88 ± 0.11-12.56 ± 1.04 %, 64.67 ± 1.51-70.14 ± 1.98 %, 47.47 ± 1.11-50.51 ± 1.30 %, 1.31 ± 0.11-1.58 ± 0.11 %, and 9.15 ± 0.31-12.07 ± 0.44 %, respectively, and the corresponding values for crop residues varied from 90.19 ± 0.77-93.67 ± 0.45 %, 7.20 ± 0.30-12.18 ± 0.66 %, 72.59 ± 2.26-78.19 ± 0.77 %, 53.70 ± 1.41-8.70 ± 0.82 %, 1.21 ± 0.09-1.97 ± 0.28 %, and 2.70 ± 0.16-6.43 ± 0.37 %, respectively. The overall mean DM, Ash, NDF, ADF, EE and CP content of Areke Atella in both AEZs ranged from 89.73 ± 0.67-93.71 ± 0.34 %, 7.55 ± 0.20-8.29 ± 0.04 %, 36.05 ± 0.42-42.38 ± 2.27 %, 30.31 ± 0.76-36.62 ± 0.49 %, 1.45 ± 0.01-1.68 ± 0.16 %, and 13.54 ± 0.27-16.43 ± 0.71 %, respectively. The overall mean DM, Ash, NDF, ADF, EE, and CP content of the indigenous fodder trees and shrubs (IFTS) varied between 90.49 ± 0.94-93.32 ± 0.58 %, 9.26 ± 0.46-11.82 ± 0.58 %, 45.29 ± .69-57.81 ± 2.80 %, 34.70 ± 0.48-36.90 ± 1.99 %, 2.34 ± 0.31-3.69 ± 0.19 %, and 8.12 ± .28-20.35 ± 0.42 %, respectively. In conclusion, IFTS had higher CP content followed by Areke atella, natural pasture grasses and crop residues. It is suggested that the supplementation of the studied IFTS and atella, particularly during the dry season when the quality of natural pasture decreases in CP content would be essential. Urea treatment of crop residues when affordable to improve its nutritional quality would be imperative to enhance livestock performance in the study area and for similar settings.

Introduction

Agriculture is the backbone of Ethiopia's economy and accounts for 34.1 % of the national domestic gross product (GDP), employs 79 % of the population, accounts for 79 % of foreign earnings, and is the major sources of raw material and capital for investment and market. Over 90 % of agriculture in the country is characterized by mixed crop –livestock farming system.

In Ethiopia, livestock farming plays a crucial role in the livelihoods of the rural population and contributes about 17–25.3 % of the GDP and 39–49 % of agricultural GDP (including the non –monetary values) and over 50 % of household income (Shapiro et al., 2017), and 12–15 % of the export earnings, and provide employment for about 60–70 % of the population (Azage et al., 2013). Intergovernmental Authority on Development (IGAD) showed that the value of the cattle draught power in put into arable production is about a quarter (26.4 %) of the value of annual crop production, and if the value of draught power services is included, the sector contributes up to ∼45 % of agricultural GDP (Azage et al., 2013). Moreover, livestock provide draught power, meat, milk, manure for fuel and soil fertility, transportation, cash income, employment, food security, insurance, savings, ritual and other social purposes (Azage et al., 2006). Traditional farming practices in the Ethiopian highlands depend on draught oxen for cultivating and threshing (Gebregziabher et al., 2013).

The current national livestock population is estimated at 65.35 million head of cattle, 39.89 million sheep, 50.50 million goats, 2.11 million horses, 8.98 donkeys, 0.38 and 7.70 million head of camel population, 59.5 million poultry and 5.92 million honey bee hives (CSA, 2020). Despite the huge livestock population and existing favorable environmental conditions, the current livestock output remains far below the country's demand. This is associated with a number of complex and inter-related factors such as feed scarcity, widespread diseases, poor genetic potential of local breeds for functional traits, undeveloped marketing system and infrastructure (Negassa et al., 2011). Feed scarcity in terms of quality and quantity as well as seasonal fluctuation was identified as the most important constraint to livestock development and productivity in Ethiopia (Adugna et al., 2012).

According to Olafadehan and Adewumi (2009), a major constraint to livestock production in developing countries is the scarcity and fluctuating quantity and quality of the year-round feed supply. As a result of this the productivity of ruminant livestock in the tropics and subtropics is limited by inadequacy of good quality and nutritive feed (Olafadehan and Adewumi, 2009). Browse fodders are useful sources of cheap feed for ruminant animals in developing countries, especially during dry seasons when herbaceous pasture grasses and legumes are scarce (Olafadehan and Okunade, 2018). The ability of their foliage to remain green and maintain their protein content makes them potential sources of protein and energy (Olafadehan, 2013). It has been reported that information on nutritional characterization of locally available feed resources in Ethiopia is inadequately addressed and where available the values are variably documented (Zinash and Seyoum, 1998).

In the present study area, livestock production is one of the most important and integral component of mixed crop-livestock farmers’ economic and livelihood activities. However, information on nutritional characteristics of the major livestock feed resources have not yet been documented in literature and the information from the current study would enable police makers and farmers to design appropriate intervention strategies. Therefore, better understanding the chemical composition of available resources will contribute to highlight potential gaps for quality improvement and proper utilization of the available feeds for livestock productivity improvement. The lack of information on the nutritional quality of feeds could result in poor performance and susceptibility to diseases of livestock. Hence, generating data on chemical composition of feeds in the current study area will serve to identify the most limiting nutrients to formulate appropriate intervention strategies to improve livestock productivity and also to serve as a basis for future research. We hypothesized that IFTS could have better nutritive value compared to other feed resources. The objective of this study was to evaluate and document chemical composition of the major feed resources in the Haru district of west Wollega Zone, Oromia Regional State, Ethiopia.

Materials and methods

Description of the study area

The study was conducted in Haru District, West Wollega zone of Oromia Regional State, Ethiopia, located at 464 km West of Addis Ababa, capital city of Ethiopia. The district is located between latitude 8°52′ N and 9°7′ N and longitude 35°41′ E and 36°10′ E. The altitude ranges from 1550 to 1950 m a.s.l. with medium altitude comprising of 86 % and low altitude 14 % of the study area. The average annual rainfall is 1853 mm. The average annual minimum and maximum temperature are 12 °C and 27 °C, respectively, with mean annual temperature of 18.3 °C.

Sample collection, preparation and analysis

The major feed resources of farmers’ high priority regarding their relative abundance and importance as livestock feed based on information obtained during group discussion with farmers were sampled separately in medium- and low-altitude agroecologies. The samples comprised the predominant natural pasture grass species, browse trees and shrubs, crop residues and byproduct of a local distilled liquor beverage. Representative samples of grass species were collected during the rainy season at flowering stage. Crop residues were sampled during dry season when they were the main source of feed and edible leaves of indigenous fodder trees and shrubs were sampled during dry season due to the fact that they were utilized in the dry season as coping strategy to feed scarcity. The feed samples collected separately from medium and low AEZs were bulked per feed type, dried under shade, thoroughly mixed and sub-sampled. From each sample type, a minimum of 300 ​g feed was dried at 65 °C for 72 h until a constant weight was obtained. The dry samples were ground in Willey mill to pass through 1 mm mesh sieve size and packed in air tight plastic containers until analysis for chemical composition at Jimma University College of Agriculture and Veterinary Medicine, Animal Nutrition Laboratory. The samples were analyzed in % DM basis separately for medium and low AEZ for determination of DM, CP, EE, CA, NDF and ADF according to AOAC (2005). Total ash content was determined by oven drying the samples at 105 °C overnight and by combusting the samples in a muffle furnace at 550 °C for 6 h (AOAC, 1995). Nitrogen (N) content was determined following the micro-Kjeldahl digestion, distillation and titration procedures (AOAC, 1995) and the CP content was estimated by multiplying the N content by 6.25. EE was determined according to the procedures of AOAC (1995). The NDF and ADF were determined according to Van Soest et al. (1991).

Statistical analysis

Collected data were statistically analysed using Statistical Package for Social Sciences (SPSS) software for window, Version 16.0 (SPSS Inc. 2007; USA). Descriptive statistics including mean values and standard error (SE) were calculated. Differences in chemical composition of feeds between AEZs were tested using analysis of variance (ANOVA). Least significance difference (LSD) at 5% significance level was used for comparison of means.

Results and discussion

Chemical compositions of natural pasture

Mean ± SE chemical composition (% of DM) of the three most commonly found natural pasture grass species in the study area are presented in Table 1. Natural pasture was reported as the most important source of feed in the study area. The most dominant and important grass species of natural pasture preferred by the farmers interviewed in the study area were Cynodon dactylon, Digitaria abyssinica and Panicum hochstetteri Steud. The results revealed that the mean DM content of the three grass species ranged from 89.64 ± 0.65 % in Digitaria abyssinica (Waraatii–local name) in low AEZ to 94.06 ± 0.27% in Panicum hochstetteri Steud (Marga gogorrii) in medium AEZ. The DM content of Digitaria abyssinica showed a significant difference (P < 0.05) between the two agro ecologies. In the medium AEZ, the DM content of grasses ranged between 89.64 ± 0.65 % in Digitaria abyssinica to 94.06 ± 0.27 % in Panicum hochstetteri Steud. In the low AEZ, the DM content of grasses ranged from 89.64 ± 0.65 % in Digitaria abyssinica to 91.25 ± 0.56 % in Cynodon dactylon (L.) Pers (Coqorsa). The chemical composition of grasses showed significant difference (P < 0.05) between the two AEZ for variables determined, except for EE in Digitaria abyssinica and Panicum hochstetteri Steud and ash content in Panicum hochstetteri Steud. The difference observed could be attributed to variation in environmental condition (climate, soil types, rainfall and temperature) of the two AEZs in the study area. This result is in agreement with Sisay (2006) who reported DM content of natural pasture ranging from 92.9 to 94.1 % in northern Gondar Zone. Zewdie (2010) also reported natural pasture DM content ranging from 91 to 92.4 % in central Rift Valley of Ethiopia. However, the DM content of native grasses in the present is higher than the result of Gashu et al. (2017) and Andualem et al. (2015) who reported DM values ranging from 35.17 % to 44.97 % and 69.63%, respectively.

Table 1

Mean ± SE of chemical composition (% of DM) of major natural pasture grass species in the study area.

Grass species	AEZ	DM	Ash	NDF	ADF	EE	CP
Digitaria abyssinica	Medium	93.16 ± 0.09a	6.76 ± 1.45a	61.84 ± 1.77a	48.02 ± 0.68a	1.80 ± 0.03	10.54 ± 0.18a
	Low	89.64 ± 0.65b	11.74 ± 0.26b	67.50 ± .51b	52.99 ± 1.33b	1.36 ± 0.11	8.54 ± 0.19
	Overall	91.40 ± 0.84	9.25 ± 1.12	64.67 ± 1.51	50.51 ± 1.30	1.58 ± 0.11	9.54 ± 0.46b
	P –value	0.01	0.000	0.037	0.029	0.17	0.002
Panicum hochstetteri Steud	Medium	94.06 ± 0.27a	6.71 ± 0.10	63.74 ± 1.09a	45.20 ± 0.71a	1.86 ± 0.24	8.46 ± 0.06a
	Low	89.80 ± 0.46b	7.06 ± 0.15	72.31 ± 1.12b	49.73 ± 0.74b	0.87 ± 0.31	9.84 ± 0.05b
	Overall	91.93 ± 0.98	6.88 ± 0.11	68.03 ± 2.04	47.47 ± 1.11	1.37 ± 0.28	9.15 ± 0.31
	P –value	0.00	0.12	0.005	0.011	0.67	0.00
Cynodon dactylon	Medium	93.28 ± 0.43	10.27 ± 0.02	65.80 ± .44	47.12 ± 0.35	1.54 ± 0.01	11.24 ± 0.35
	Low	91.25 ± 0.56	14.85 ± 0.44	74.48 ± .79	51.62 ± 1.51	1.08 ± 0.04	12.90 ± 0.43
	Overall	92.26 ± 0.55	12.56 ± 1.04	70.14 ± 1.98	49.37 ± 1.22	1.31 ± 0.11	12.07 ± 0.44
	P –value	0.05	0.000	0.001	0.044	0.00	0.039

Means followed by different superscript letters within a column for each feed type are significantly different at P < 0.05; SE = standard error of means; DM = Dry matter; CP = Crude Protein; EE = Ether Extract; NDF = Neutral Detergent Fiber; ADF = Acid Detergent Fiber.

The CP content of grasses ranged from 8.46 ± 0.24 % in Panicum hochstetteri Steud to 12.9 ± 0.43% in Cynodon dactylon, with significantly difference (P < 0.01) between the study locations. The highest CP was observed in Cynodon dactylon and all grass species had CP content above 7% required for maintenance requirement of ruminants. The variation in CP content of grasses between the AEZs might be due to species, agro ecology and soil fertility. This result is in agreement with findings of Gashu et al. (2017), who report natural grass CP contents of 10 to 9.62 % in Gasera and Ginnir Districts and contrary to Andualem et al. (2015) and Deribe et al. (2013) who reported natural grass CP content of 3.67–4.25 % and 8.38 %. The CP content of native grasses in the present study is higher than the minimum level of 7% for animals in the tropics (Van Soest, 1994; Mlay et al., 2006). According to Van Soest (1994), feed with CP level less than 7.5 % inhibit voluntary feed intake and declines the activity of microbial action, resulting in lower digestibility of roughages.

EE content of grasses ranged from 0.87 ± 0.31 % in panicum hochstetteri Steud in low AEZ to 1.86 ± 0.24 % in panicum hochstetteri in medium AEZ. EE content of grass showed no significant difference (P > 0.05) between study AEZs, except Cynodon dactylon (L.) Pers (P < 0.05). This finding concur with the results of Girma et al. (2014) who found natural pasture EE content of 1.3–1.5 %.

The ash content of the grass ranged from 6.71 ± .10 % in Panicum hochsteeri Steud to 14.85 ± .44 % in Cynodon dactylon (L.) Pers. The ash contents of Digitaria abyssinica and Cynodon dactylon (L.) Pers showed a significantly difference (P < 0.05) between the AEZs in the study area. These results are not in agreement with that of Habtamu et al. (2013) who reported the ash content of natural grass was ranged from 12.5 %–16.7 %.

The mean NDF contents of natural grass ranged from 61.84 ± 1.77 % in Digitaria abyssinica to 74.48 ± .79 % in Cynodon dactylon (L.) Pers. Grass NDF content in both AEZs was less than 65 % and can be categorized as medium in quality (Singh and Oosting, 1992). The ADF content of grass samples ranged from 45.20 % in Panicum hochsteeri Steud to 52.99 ± 1.33 % in Digitaria abyssinica. The ADF contents of Digitaria abyssinica, panicum ehochstetteri Steud and Cynodon dactylon (L.) Pers showed significantly (P < 0.05) higher in low AEZ than in medium AEZ of the study area. This variation could be attributed to the species of the grass, soil, temperature, and amount and intensity of rainfall.

Chemical composition of major crop residues

The chemical composition of crop residues is presented in Table 2. The DM contents of maize stover, and bean, barley, wheat, and teff straws showed a significant difference (P < 0.05) between the two AEZs of the study area. The DM contents of crop residues ranged from 88.66 ± 0.76 % in teff (Eragrostis tef) straw in low AEZ to 94.60 ± 0.17 % in faba bean straw in medium AEZ. The DM content of teff straw in low AEZ of the current study is lower than that of the national average value of (91.9 %), whereas that of faba bean is found to be higher than the national average reported by Adugna (2008). The DM content of crop residues obtained in the current study are in agreement with that of Zewdie (2010) and Girma et al. (2014). who reported DM content of crop residues higher than 90% and 89.86 %–93.6 %, respectively. Wonchesa et al. (2018) also reported the DM content of crop residues ranging from 91 to 94 %. The DM content of teff straw and sorghum stover reported in the present study are lower than the results of Zewdie (2010) who found 93.07 % and 94.19 ± 0.25 % DM in teff straw and 93.06 ± 0.16 % and 93.63 ± 0.29 % in sorghum straw in medium and low AEZs, respectively. The variation observed in DM content of crop residues between the study AEZ in the present study might be attributed to the difference in management practices, soil fertility, species and variety of the crops.

Table 2

Mean ± SE chemical composition of major crop residues (% DM basis) in the study area.

Feed stuff	AEZ	DM	Ash	NDF	ADF	EE		CP
Maize stover	Medium	93.97 ± 0.36a	9.35 ± 0.14a	74.21 ± 0.61a	51.02 ± 0.72a	2.06 ± 0.02a		3.56 ± 0.06a
	Low	91.13 ± 0.57b	6.89 ± 0.24b	82.48 ± 0.98b	59.73 ± 1.74b	1.51 ± 0.02b		3.99 ± 0.07b
	Overall	92.55 ± 0.70	8.12 ± 0.57	78.19 ± 0.77	55.37 ± 2.12	1.79 ± 0.12		3.78 ± 0.10
	P –value	0.01	0.00	0.002	0.010	0.000		0.009
Bean straw	Medium	94.60 ± 0.17a	10.06 ± 0.13a	75.87 ± 2.55	51.23 ± 0.78a	1.99 ± 0.05a		7.20 ± 0.09a
	Low	92.74 ± 0.35b	6.33 ± 0.17b	69.31 ± 2.89	56.31 ± 0.87b	1.35 ± 0.09b		5.65 ± 0.29b
	Overall	93.67 ± 0.45	8.19 ± 0.84	72.59 ± 2.26	53.77 ± 1.25	1.67 ± 0.15		6.43 ± 0.37
	P –value	0.01	0.00	0.164	0.012	0.003		0.007
Barley straw	Medium	93.68 ± 0.96a	10.92 ± 0.85	72.21 ± 0.58	50.92 ± 1.40a	2.45 ± 0.31		4.99 ± 0.11
	Low	89.72 ± 0.35b	10.10 ± 0.96	75.30 ± 1.53	56.47 ± 0.46b	1.49 ± 0.28		4.72 ± 0.08
	Overall	91.70 ± 1.00	10.51 ± 0.60	73.76 ± 1.01	53.70 ± 1.41	1.97 ± 0.28		4.86 ± 0.08
	P –value	0.02	0.56	0.133	0.020	0.83		0.116
Wheat straw	Medium	94.10 ± 0.51	12.73 ± 0.28	77.63 ± 1.73	53.42 ± 1.48	1.38 ± 0.09a		3.02 ± 0.05a
	Low	90.94 ± 1.22	11.62 ± 1.33	72.14 ± 1.30	60.83 ± 2.51	1.03 ± 0.08b		2.39 ± 0.16b
	Overall	92.52 ± 0.92	12.18 ± 0.66	74.88 ± 1.56	57.13 ± 2.11	1.21 ± 0.09		2.70 ± 0.16
	P –value	0.08	0.46	0.064	0.292	0.042		0.019
Teff straw	Medium	91.71 ± 0.20a	8.36 ± 0.44	79.61 ± 0.70	54.56 ± 0.29	1.57 ± 0.04		4.02 ± 0.02a
	Low	88.66 ± 0.76b	7.20 ± .23	75.80 ± 1.25	56.17 ± 1.30	1.48 ± 0.10		3.21 ± 0.03b
	Overall	90.19 ± 0.77	7.78 ± 0.34	77.71 ± 1.07	55.36 ± 0.70	1.52 ± 0.06		3.62 ± 0.18
	P –value	0.02	0.08	0.057	0.292	0.442		0.000
Sorghum stover	Medium	94.19 ± 0.25a	7.49 ± 0.28	78.23 ± 1.23a	57.14 ± 0.36a	1.65 ± 0.04a		3.89 ± 0.11a
	Low	93.06 ± 0.16b	6.90 ± 0.55	70.65 ± 2.34b	60.27 ± 0.89b	1.15 ± 0.09b		3.17 ± 0.06a
	Overall	93.63 ± 0.29	7.20 ± 0.30	74.44 ± 2.07	58.70 ± 0.82	1.40 ± 0.12		3.53 ± 0.17
	P –value	0.020	0.39	0.046	0.031	0.006		0.004

Means followed by different superscript letters within a column for each feed type are significantly different at P < 0.05; SE = standard error of means; DM = Dry matter; CP = Crude Protein; EE = Ether Extract; NDF = Neutral Detergent Fiber; ADF = Acid Detergent Fiber.

The ash contents of crop residues ranged from 7 % to 12 % in medium AEZ and 6 %–11 % in low AEZ of the present study area. The ash contents of maize stover and Faba bean showed a significant different (P < 0.01) between the two AEZs. This different could be due to variation in crop variety, soil fertility, temperature and harvesting techniques.

The NDF content of crop residues ranged from 72.59 ± 2.26–78.19 ± 0.77 % and showed no significant difference (P < 0.05) between the AEZs, except maize and sorghum stovers. The NDF content of crop residues obtained in the current study are higher than the range of 66.5 %–77.2 % reported by Girma et al. (2014). NDF content of roughage feeds with less than 45 % is categorized as a high quality feed and 45–65 % as medium quality feed (Singh and Oosting, 1992). Based on these categories, the NDF content of crop residues in our study was high. NDF content of feeds above 55% was reported to limit DM intake (Van Soest, 1982).

In medium AEZ of the study area, the average ADF contents of maize stover, bean straw, barley straw, wheat straw, teff straw and sorghum stover were 51.02 ± 0.72 %, 57.36 ± 1.44 %, 55.26 ± 1.92 %, 61.76 ± 0.60 %, 58.89 ± 1.60 %, and 60.81 ± 0.52 %, respectively, whereas the respective values in low AEZ were 59.73 ± 1.74 %, 56.31 ± 0.87, 56.47 ± 0.46, 60.83 ± 2.51, 56.17 ± 1.30 and 0.27 ± 0.89 %, respectively. In both AEZs of the study area, the highest ADF content was recorded in sorghum stover while the lowest was observed in bean straw.

The EE content of maize stover, bean straw and teff straw showed significant difference (P < 0.05) between both AEZs of the study area. The EE content of crop residues ranged from 1.03 ± 0.08 % in wheat straw in low AEZ to 2.45 ± 0.31 % in barley straw in medium AEZ. In medium AEZ, barley straw and maize stovers were found to be higher in EE content, whereas EE content of wheat straw and sorghum stover were found to be lower in low AEZ of the study area.

The CP content of crop residues ranged from 2.39 ± 0.16 % in wheat straw in low AEZ to 7.20 ± 0.09 % in bean straw in medium AEZ of the study area. CP content of maize stover, bean straw, barley straw, teff straw and sorghum stover showed significant difference (p < 0.05) between both AEZs. The CP content of crop residues in this study are higher than the findings by Wonchesa et al. (2018) who found 2.63 % in barley to 5.54 % in field pea. In earlier studies, Girma et al. (2014) and Adugna (2008) who reported CP content of crop residues ranging from 2.9 –5.9 % and 2.8 %–5.6 %, respectively. The CP content of crop residues recorded in the present study is lower than the minimum level (7% CP) required for rumen microbial function (Van Soest, 1982). In the current study, cereal straws and stovers varied greatly in their CP content, which could be attributed to differences in crop species and variety, agronomic practices (fertilizer application), soil and temperature, stage of growth and variation in different parts of the same plant (Reed et al., 1974).

Chemical composition of Areke atella

The chemical composition of Areke atella (byproduct of local distilled liquor beverage in Ethiopia) is presented in Table 3. In medium AEZ, the DM, Ash, NDF, ADF, EE and CP content of Areke atella were 93.71 ± 0.34, 8.29 ± 0.04, 36.05 ± 0.42, 30.31 ± 0.761.68 ± 0.16 and 13.54 ± 0.27, respectively, whereas the corresponding values in low AEZ were 89.73 ± 0.67, 7.55 ± .20 and 42.38 ± 2.27, 36.62 ± 0.49, 1.45 ± 0.01, and 16.43 ± 0.71 %, respectively. The highest DM content of Areke atella may be attributed to the removal of high amount of moisture during the distillation and filtration processes of extracting the liquor (Fekede et al., 2015). The CP content of Areke atella recorded in this study is lower than the results of Kasahun et al. (2012) and Adugna (2008) who found 17.6% and 17.8 %, respectively. In the present study, the CP content of Areke atella was significantly higher than the CP content of natural grass and crop residues. This shows that Areke atella could be used as strategic protein supplementation, especially during the dry season when CP content of natural pasture is below the level required for maintenance of ruminants.

Table 3

Mean ± SE of chemical composition of Areke atella (% of DM) in the study area.

Parameter	Agro-ecological zone		Overall mean	P –value
	Medium	Low
DM	93.71 ± 0.34a	89.73 ± 0.67b	91.72 ± 0.95	0.01
Ash	8.29 ± 0.04a	7.55 ± 0.20b	7.92 ± 0.19	0.02
NDF	36.05 ± 0.42a	42.38 ± 2.27b	39.21 ± 1.75	0.05
ADF	30.31 ± 0.76a	36.62 ± 0.49b	33.46 ± 1.47	0.002
EE	1.68 ± 0.16	1.45 ± 0.01	1.56 ± 0.09	0.227
CP	13.54 ± 0.27a	16.43 ± 0.71	14.98 ± .73b	0.019

Means followed by different superscript letters within a column for each feed type are significantly different at P < 0.05; SE = standard error of means; DM = Dry matter; CP = Crude Protein; EE = Ether Extract; NDF = Neutral Detergent Fiber; ADF = Acid Detergent Fiber.

Chemical composition of indigenous fodder trees and shrub

Chemical compositions of the major browse species in the study area are presented in Table 4. The respondents indicated that indigenous fodder trees and shrubs (IFTS) are important source of supplementary feed for livestock in dry season. This could be due to their characteristics to stay green longer during dry season than natural pasture. The DM content of IFTS was higher (93.32 ± 0.58 %) in the medium AEZ than in low AEZ (88.59 ± 0.55 %). The average DM content of Vicus vasta Forssk was 94.05 ± 0.15 % and 91.84 ± 0.32 % in medium and low AEZs, respectively, with overall mean of 92.94 ± 0.52 %, with significantly different (P < 0.05) between the AEZs. In medium AEZ, the highest DM content was obtained in Ficus sur forssk (94.51 ± 0.34 %) and the lowest was found in Vernonia amygdalina (92.39 ± 0.72 %). Whilst the highest DM content was recorded in Ficus sur forssk (Harbuu) (92.39 ± 0.28 %) and the lowest was obtained in Vernonia amygdalina (88.59 ± 0.55 %) in the low AEZ. The difference in DM contents of IFTS between medium and low AEZs could be attributed to variation in climate or environmental factors. These findings are in agreement with that of earlier reports (Belete et al., 2012; Deribe et al., 2013) which noted that the DM content of browse species ranged from 88 % to 94.55 %. Yisehak (2013) also reported DM content of browse species ranging from 92 %–96.85 %. The DM content of IFTS recorded in the current study are higher than the value of 57.08 % reported by Andualem et al. (2015) in Essera District, Southern Ethiopia. This difference might be attributed to the variation in species of browse trees and climate of the study areas.

Table 4

Mean ± SE of chemical composition of indigenous fodder trees and shrubs leaves (% in DM basis) in the study area.

Species	Local name (Afaan Oromo)	AEZ	DM	Ash	NDF	ADF	EE	CP
Ficus vasta forssk	Qilxuu	Mid AEZ	94.05 ± 0.15a	12.80 ± 0.12a	46.19 ± 0.57	37.83 ± 0.36a	3.19 ± 0.35a	8.66 ± 0.29a
		Low AEZ	91.84 ± 0.32b	9.27 ± 0.13b	39.74 ± 2.78	35.76 ± 0.29b	2.02 ± 0.21b	7.59 ± 0.17b
		Overall	92.94 ± 0.52	11.03 ± 0.79	42.96 ± 1.92	36.80 ± 0.51	2.61 ± 0.32	8.12 ± 0.28
		P –value	0.000	0.000	0.085	0.011	0.045	0.034
Vernonia amygdalina	Eebicha	Mid AEZ	92.39 ± 0.72a	8.27 ± 0.05a	53.71 ± 0.49	32.57 ± 0.28a	3.80 ± 0.02a	14.36 ± 0.09a
		Low AEZ	88.59 ± 0.55b	10.24 ± 0.31b	54.38 ± 2.31	41.23 ± 1.02b	2.71 ± 0.24b	12.61 ± 0.38b
		Overall	90.49 ± 0.94	9.26 ± 0.46	54.04 ± 1.07	36.90 ± 1.99	3.25 ± 0.27	13.49 ± 0.43
		P –value	0.01	0.000	0.792	0.001	0.010	0.011
Ficus sur Forssk	Harbuu	Mid AEZ	94.51 ± 0.34a	10.17 ± 0.04a	44.29 ± .29	31.71 ± 1.41	3.04 ± 0.01a	12.62 ± 0.05a
		Low AEZ	92.39 ± 0.28b	12.03 ± 0.30b	46.75 ± 1.22	36.65 ± 1.54	1.64 ± 0.04b	11.57 ± 0.15b
		Overall	93.45 ± 0.51	11.10 ± 0.44	45.52 ± .79	34.18 ± 1.45	2.34 ± 0.31	12.09 ± 0.24
		Pvalue	0.01	0.00	0.122	0.077	0.000	0.003
Ficus ​thonningii blume	Dambii	Mid AEZ	93.32 ± 0.58a	12.08 ± 0.26a	48.87 ± .90a	38.35 ± 0.80a	3.88 ± 0.53	16.27 ± 0.13a
		Low AEZ	90.78 ± 0.53b	7.04 ± 0.06b	56.23 ± .76b	47.24 ± 0.81b	2.76 ± 0.27	12.94 ± 0.28b
		Overall	92.05 ± 0.67	9.56 ± 1.13	52.55 ± 1.73	42.80 ± 2.05	3.32 ± 0.37	14.61 ± 0.76
		P –value	0.03	0.000	0.003	0.001	0.136	0.000
Sapium ellipticum	Bosoqaa	Mid AEZ	93.34 ± 0.40a	10.57 ± 0.06a	52.10 ± .58a	34.70 ± 0.48a	4.10 ± 0.03a	12.53 ± 0.07
		Low AEZ	89.58 ± 1.02b	13.07 ± 0.32b	63.52 ± 2.53b	37.31 ± 0.68b	3.27 ± 0.08b	13.14 ± 0.32
		Overall	91.46 ± 0.97	11.82 ± 0.58	57.81 ± 2.80	36.00 ± 0.69	3.69 ± 0.19	12.83 ± 0.20
		Pvalue	0.03	0.00	0.012	0.035	0.001	0.138
Sesbania sesban	Sasbaniyaa	Mid AEZ	94.19 ± 0.49	12.46 ± 0.92	44.00 ± 0.74a	37.83 ± 0.36a	2.97 ± 0.03a	17.63 ± 0.73a
		Low AEZ	89.96 ± 1.65	9.30 ± 1.57	46.57 ± 0.42b	35.76 ± 0.29b	2.54 ± 0.05b	23.08 ± 0.43b
		Overall	92.07 ± 1.22	10.88 ± 1.08	45.29 ± 0.69	36.80 ± 0.51	2.76 ± 0.10	20.35 ± 0.42
		P –value	0.07	0.16	0.04	0.011	0.002	0.003

Means followed by different superscript letters within a column for each feed type are significantly different at P < 0.05; SE = standard error of means; AEZ = Agro ecological zone; DM = Dry matter; CP = Crude Protein; EE = Ether Extract; NDF = Neutral Detergent Fiber; ADF = Acid Detergent Fiber.

The average ash content of indigenous browse tree and shrubs ranged from 7.04 ± 0.06% in Ficus thonningii blume (Dambii) to 13.07 ± 0.32 % in Sapium ellipticum in low AEZ wheras from 10.17 ± 0.04 % in Ficus sur forssk (Harbuu) to 12.80 ± 0.12 % in Ficus vasta Forssk (Qilxuu) in medium AEZ. The ash contents of Ficus vasta Forssk (Qilxuu), Vernonia amygdalina, Ficus thonningii blume and Sapium ellipticum showed significant difference (P < 0.05) between the two agro ecological zones of the study area. The result of the ash contents of IFTS in the current study concurs with that of Deribe et al. (2013) who reported ash contents of browse species ranging from 8.07 to 13.39 % of DM. In contrast, the result obtained in the present study are higher than that of Endale (2015) who reported ash content of indigenous browse species was 5%.

The mean ADF content of IFTS varied from 25.99 ± 1.09 % in Seasbania sesban to 38.35 ± 0.80 % in Ficus thonningii blume in medium AEZ whereas it ranged from 34.19 ± 1.02 % in Sesbania sesban to 47.24 ± 0.81 % in Ficus thonningii blume in low AEZ. These findings are higher than the value of 15.55 % ADF content of browse species reported by Andualem et al. (2015) in Essera District, Southern Ethiopia.

The CP content of IFTS showed significant difference (P < 0.05) between both AEZs, except for Sapium ellipticum. The average CP content of IFTS ranged from 8.12 ± .28 % in Vicus vasta Forssk to 20.35 ± 1.28 % in Sesbania sesban. The analysis revealed that Sesbania sesban had the highest CP content amongst the IFTS sampled. These findings are comparable with results of previous studies (Belete et al., 2012; Andualem et al., 2015) who reported CP content of fodder tree and shrubs ranging from 8.9 % to 20.9 %. Deribe et al. (2013) also reported CP level of 16.40% in browse species in mixed farming system of Southern Ethiopia. Browse species can be used as good protein source to supplement low quality basal diets, especially during the dry season when the quality and quantity of green herbages is limited (Mekonnen et al., 2009). The higher CP content of browse species in the current study area could make them a potential source of strategic supplements to feeds of poor quality such as crop residues and natural pasture during dry season because their CP content was found to be higher than the minimum thresh level of 7 % CP required for optimal rumen function and feed intake in ruminant livestock (Van Soest, 1982). In this study, the average crude fat (EE) content of IFTS varied from 1.64 ± 0.04 % in Ficus sur forssk to 3.27 ± 0.08 % in Sapium ellipticum in low AEZ. Whereas the EE of IFTS ranged from 2.97 ± 0.03 % in Sesbania sesban to 3.88 ± 0.53 % in Ficus thonningii blume at medium AEZ.

Conclusions

From the results of this study, it is concluded that IFTS had higher CP content followed by Areke atella, natural pasture grass species and crop residues in both AEZs. The highest CP content of indigenous fodder trees and shrubs and areke atella implies their suitability and potential protein supplementation, especially during the dry season when CP content of natural pasture and crop residues is low. The CP content of crop residues was found to be below the critical level (7% CP) required for maintenance, optimum rumen function and feed intake, resulting in low livestock productivity. It is suggested that improved forage production and urea treatment of crop residues to improve their nutritive value or their supplementation with good energy and protein sources of feeds would be imperative to enhance productivity and sustainable development of livestock in the study area. Further study should be directed towards the supplementation of IFTS and Areke atella in practical animal feeding trials to validate their supplementary values and level of inclusion in animal diet.

Declarations

Author contribution statement

Tamene Bayissa: Conceived and designed the experiments; Performed the experiments; Analyzed and interpreted the data; Wrote the paper.

Belay Dugumaa; Kassahun Desalegn: Conceived and designed the experiments; Analyzed and interpreted the data; Wrote the paper.

Funding statement

This work was supported by Jimma University, Ethiopia.

Data availability statement

Data will be made available on request.

Declaration of interests statement

The authors declare no conflict of interest.

Additional information

No additional information is available for this paper.