Comparative nutritional evaluation of the leaves of Bambusa balcooa (Beema) and Oxytenanthera abyssinica (A. Rich.) Munro bamboos, and the straws of AGRA and AMANKWATIA rice varieties

Abstract

In this study, the chemical and nutritional characteristics of the leaves of Bambusa balcooa and Oxytenanthera abyssinica bamboos, and the straws of AGRA and Amankwatia rice varieties were evaluated using three analytical methods; proximate analysis, detergent fiber analysis and in vitro gas production. Data were analyzed using General Linear Model procedures in Minitab Statistical Software at a 5% significant level. Results showed that the leaves of B. balcooa had the highest (P < 0.05) levels of dry matter (~925 gkg⁻¹), ash (~179 gkg⁻¹DM), and dry matter intake (~2.3%). The leaves of O. abyssinica had the highest levels of organic matter (~879 gkg⁻¹DM) and crude protein (~128 gkg⁻¹DM). AGRA rice straw recorded the maximum (P < 0.05) level of crude fiber (~283 gkg⁻¹DM) and neutral detergent fiber (~590 gkg⁻¹DM). The highest (P < 0.05) gas production (~10.2 mL) and fermentable fraction (~10.5 mL) were recorded for O. abyssinica, at a rate of 0.067 mLh⁻¹. The results further showed a strong negative correlation between crude protein and fiber fractions of the feeds (r = - 0.959 to − 0.977, P < 0.001) but a strong positive correlation with organic matter digestibility (r = 0.722, P < 0.001), energy levels (r = 0.886 to 0.922, P < 0.001), and in vitro gas production (r = 0.897 to 0.881, P < 0.001). In conclusion, all the feeds exhibited promising nutritional characteristics and their inclusion in the ration as mix feeds could enhance the bulk and nitrogen content.

Keywords:

• Dry season
• forage supply
• bamboo leaves
• rice straws
• nutritional evaluation

PUBLIC INTEREST STATEMENT

If you are an animal lover or interested in sustainable agriculture, you will be thrilled to know that we have identified some exciting new feed options for livestock! In this study, we evaluated the nutritional value of two types of bamboo leaves and rice straw as potential feed sources for ruminants in the tropics, where finding nutritious feed during the dry season can be a challenge. The results were impressive, with the bamboo types, distinctively showing superior levels of nutrients, and in vitro ruminal yields. Additionally, all the feeds had enough fibre to enhance rumen microbiome. These findings could have a significant impact on livestock production and food security in the tropics, where farmers may struggle to keep their animals fed and healthy during the dry season. Therefore, this research could help farmers raise healthy, sustainable livestock and ensure a stable food supply for their communities.

1. Introduction

The global population is estimated to increase to 9.1 billion by 2050, requiring food production to increase by 70% to meet demands for adequate nutrition (Lagrange et al., 2015; Matthews et al., 2019). Livestock products make up 18% of global calories and 34% of global protein consumption, providing essential micro-nutrients such as vitamin B12, iron, and calcium (CGIAR, 2019). Keeping livestock offers numerous extra benefits to livelihood, including manure production and drought power, and provides a secure source of income for over 500 million people living in poverty, primarily in rural areas (CGIAR, 2019). Livestock like cows, sheep, and goats are important for meat, milk, and other things like skins and fertilizer. To keep them healthy and productive, proper feeding is the most important thing to think about when starting a business with these animals.

The shortage and high cost of conventional ruminant feed can be a major issue for ruminant production. Alternative feed sources, such as crop residues and underutilized fodder plants, provide a budget-friendly and readily available solution. Utilizing these alternative feed sources can reduce financial pressure and maintain the efficiency of ruminant enterprises in areas where conventional feed is scarce or expensive, promoting animal health and growth. An argument against industrial meat production is the competition for resources between animal feed and human food. However, ruminants such as cattle, sheep, and goats are valuable because they can convert non-edible agricultural and industrial waste products into useful resources (Bender, 1992) The digestive system of ruminants, such as cattle, sheep, and goats, is biologically distinctive and provides an ideal environment for the digestion of feed components through microbial processes. This results in the effective breakdown of ingested components, including fiber, into protein-rich end-products like meat and milk (Aquino et al., 2020; Gummert et al., 2020). As a result of their unique digestive system, ruminants have the ability to thrive on a wide range of alternative feed sources, granting them a competitive edge over monogastric animals.

In many developing countries, including Ghana, the availability of high-quality feed for ruminants is seasonal and varies with the wet and dry seasons. During the dry season, feed scarcity can become a problem, but after the harvest season, cereal crop residues and other unconventional agro-based by-products become readily available and can serve as a practical and affordable source of feed for ruminants (Aquino et al., 2020). Despite their affordability and availability, these agro-based products are often underutilized and the nutritional information about them is often unknown. This study focuses on two of these underutilized feed resources, rice straws and bamboo leaves, and their potential for feeding ruminant livestock in Ghana and other areas.

According to the OECD/FAO (2020), global cereal production is expected to grow by 375 million tons and reach 3,054 million tons by 2029. This growth is driven by the increasing consumption of rice (Oryza sativa), which is projected to rise by 69 million tons. The majority of the increase in rice consumption is expected to occur in Asia and Africa, where per capita rice consumption is projected to increase by approximately 4 kilograms by 2029 (OECD/FAO (2020). Improved rice varieties created through advances in biotechnology and the utilization of inputs and better agricultural practices are expected to result in increased yields, meeting the projected demand. This is projected to generate a large quantity of crop residues beneficial for the livestock industry, estimated at around 330 million metric tons in heavy rice-producing countries (Robinson, 2006; Singh et al., 2016). Globally, more than 1,000 million tons per year of rice straw are produced (De et al., 2020).

Nwanze et al. (2006) reported that rice is the fastest-growing food source in Africa. In Ghana, it is a food and cash crop that sustains the bulk of the country’s rural residents (MoFA, 2010). Statistics show that Ghana produced between 181,000 and 622,000 MT of milled rice between 2008 and 2020, ranging from 302,000 to 987,000 MT of paddy rice, with a consumption of about 1,450,000 MT. This amounts to a per capita intake of approximately 45.0 kg annually (MoFA Ministry of Food and Agriculture, 2023). About 20 different rice seed varieties have been registered by the Council for Scientific and Industrial Research (CSIR) in the country, with AGRA and AMAKWATIA being a couple of the long grain types that farmers choose because of their great yield potential (MoFA, 2023). Rice husk and rice straw are two different types of residue produced during rice cultivation. In locations where feed is sparse throughout the prolonged dry season, rice straw is particularly crucial as a source of energy for grazing animals (Ansah et al., 2017). In the lean months or when high-quality roughages are hard to come by, ruminant livestock farmers can gather and store rice straws from paddy fields as a reserve feed for their animals. Unfortunately, the open burning of rice straw by paddy farmers in Ghana and other unsustainable uses of the material represents a serious threat to the environment. In addition to producing a significant quantity of greenhouse gas (GHG) emissions, this act also wastes a useful by-product, which reduces the supply of animal feed (Singh et al., 2016). To enhance the quality and availability of feed for resource-constrained ruminant livestock farmers during the dry season, the use of fodder trees and shrubs is considered a potential technique, according to Sultana et al. (2015). Therefore, there is a growing interest in using trees and shrubs as alternative and/or supplement to most crop residues as feed for cattle, sheep, and goats in many parts of the world, with encouraging results (Ayuk et al., 2007).

Bamboo, known as the wonder plant, has a woody culm (stem) and is considered the strongest and fastest-growing grass on earth (Zehui, 2007). It is a valuable commodity, supplying an estimated US$2 billion per year to the global trade market (Zipporah, 2016). Due to its high biomass production, fast growth, and adaptability to dry conditions, bamboo can serve as an alternative source of fodder for ruminants and help maintain their body weight during the dry season (Andriarimalala et al., 2019). Bamboo belongs to the sub-family of Bambusoideae, Family Gramineae (Poaceae) (Armstrong, 2008), with a classification of Class: Liliopsida, Subclass: Commenlinidae; Order: Cyperales and Tribe Bambusinae (Tekpetey, 2011). Although there is no accurate inventory of the bamboo resources in Africa, it is believed that they span roughly 2.8 million hectares, or about 13% of the world’s total bamboo cover (Lobovikov et al., 2007). In Ghana, four main species of bamboo have been documented: Bambusa ventricosa McClure, Oxytenanthera abyssinica (A. Rich.) Munro, and two varieties of Bambusa vulgaris: B. vulgaris Schrad. ex J. C. Wendl. var. vulgaris Hort. and B. vulgaris Schrad. ex J. C. Wendl. var. vittata Rivière (Antwi-Boasiako et al., 2011). Among these species, B. vulgaris is the most common, accounting for over 95% of total bamboo resources in Ghana (Antwi-Boasiako et al., 2011). Recently, a superior clone selected from Bambusa balcooa called Beema has been introduced into the country by INBAR-Ghana, which may provide additional benefits for local farmers. While bamboo has numerous uses, including biomass energy, pharmaceuticals, building materials, chemicals, and environmental purposes, such as erosion control and carbon sequestration (Antwi-Boasiako et al., 2011; Halvorson et al., 2010; INBAR, 2019), the majority of its uses are limited to the stems/poles, roots, and extracts from the plant, with little or no use for the leaves. However, studies have shown that bamboo has the potential to serve as a source of fodder, feed, and woody material for several livestock species, including cattle, sheep, and goats in many Asian and African countries (Asaolu et al., 2009; Halvorson et al., 2010; Hayashi et al., 2005; Sasu et al., 2022, 2023). As bamboo is a type of grass, not a tree, it continues to grow when cut, making it a promising source of fodder and feed. Therefore, bamboo can be an alternative source of fodder for ruminants and help maintain their body weight during the dry season. Bamboo agroforestry practitioners and researchers have stated that additional study and development are required to enhance the use of bamboo as a plant for animal fodder in a number of developing nations (Antwi-Boasiako et al., 2011; INBAR, 2019). Similar to rice straw, there has not been much discussion regarding the use of bamboo leaves as fodder in the Ghanaian context, and there is a paucity of information on their feeding value, hence they are categorized as underutilized fodder resources.

To address this gap, the objective of the present study was to evaluate the chemical composition, and nutritional characteristics of the leaves of Bambusa balcooa (Beema), Oxytenanthera abyssinica (A. Rich.) Munro, and compared them to the straws of AGRA and AMANKWATIA rice varieties.

2. Materials and methods

2.1. Study Area

The research was conducted at the Livestock Section of the Department of Animal Science, Kwame Nkrumah University of Science and Technology (KNUST), Kumasi, Ghana, during the dry period from September 2021 to November 2021. The study location is situated in the semi-deciduous humid forest zone of Ghana, which is characterized by a bimodal rainfall pattern of 1300 mm annually. The average daily temperature during the study period was 26◦C, with a daily temperature range of 20 to 35◦C. In the wet season, the relative humidity varied from 97% in the morning to as low as 20% in the late afternoon, with daily temperatures ranging from 20 to 35◦C and relative humidity of 67–80% (Unpublished 2021 meteorological data, Department of Animal Science, KNUST).

2.2. Source of leaves, sampling procedure, and sample preparation

Fresh leaves of Bambusa balcooa (Beema) and Oxytenanthera abyssinica (A. Rich.) Munro, and straws of AGRA and AMANKWATIA rice varieties were collected from the INBAR1¹ agroforestry site and paddy fields of The Crop Research Institute (CRI) Division of The Centre for Scientific and Industrial Research (CSIR), Fumesua, Kumasi, Ghana, respectively. The sampling was carried out in three separate locations for each plant biomass. Two distinct plant branches on each bamboo species that were not conspicuously over-matured were considered, and the leaves were plucked out. Samples of the straws were taken from three different locations on the rice field. Approximately 3.0 kg of representative samples of each plant biomass were packed in air-tight bags and transported to the laboratory for further analyses.

At the laboratory, triplicate samples of each plant biomass were prepared based on the three sampling locations to get the statistical repetitions. The samples were chopped into smaller pieces, allowed to air dry in a room for 24 hours, and then dried in an oven at 60◦C for 48 hours to achieve a constant weight. The oven-dried samples were coarsely milled individually using a laboratory mill (Wiley Mill²) to pass through a 2 mm screen and then placed in Ziploc bags for chemical and nutritional analyses.

2.3. Laboratory Chemical analyses

The proximate analytical procedure was employed following the standard procedures of the Association of Official Analytical Chemists (AOAC, 1990) to determine the nutritional composition of the collected plant biomass samples. The procedure included the determination of dry matter (DM), crude protein, ether extract (EE), crude fiber (CF), and ash. Dry matter (DM) was determined by drying the samples in a hot air oven at 105 ºC for 8 hours, while total ash was analyzed by incineration at 550ºC for 8 hours in a muffle furnace. Crude protein (was calculated from the nitrogen values (CP = N concentration × 6.25) using the Kjeldahl method (Shaw, 2006). All amino acids contain N, in the amino group, and plant and muscle proteins contain on average 16% N, so multiplying the N concentrations by 6.25 (i.e. 100% divided by 16%) gives a value for the protein content of the experimental plant biomasses. To determine the crude fiber content, the samples were subjected to acid and base digestion before incineration. The nitrogen-free extract (NFE) was estimated using the formulae described by Agolisi et al. (2020b).

(1) $NFE,\mathrm{\%}=100-\hspace{0.17em}\left(\mathrm{\%}moisture+\mathrm{\%}fat+\mathrm{\%}crudefibre\mathrm{\%}+\mathrm{\%}Protein+\mathrm{\%}ash\right)$(1)

To determine the contents of neutral detergent fiber (NDF) and acid detergent fiber (ADF), the ANKOM³ 2000 Automated Fiber Analyzer was used, and standard procedures as described by Van Soest et al. (1991) were followed. Acid detergent lignin (ADL) was evaluated by subjecting the acid detergent fiber residue to 72% sulphuric acid. All analyses were carried out in triplicate for each sample of the collected plant biomass.

2.4. Laboratory In vitro ruminal analysis

Rumen fluid used for the in vitro studies was obtained from 10 male N’dama beef cattle with an average age of 3 ½ years old and live weight of 297 kg. The cattle were slaughtered at the Kumasi Abattoir Company Limited, Ghana, and the rumen digesta was collected as soon as the carcasses were opened and placed in a pre-warmed vacuum flask. The collected digesta was then strained with a four-layered cheese cloth under constant flushing with carbon dioxide to maintain anaerobic conditions. The resulting rumen liquor was then mixed with buffer in a ratio of 1:4 (liquor: buffer) following the procedure of Menke et al. (1979). Two hundred milligrams of each plant sample were incubated with a rumen liquor buffer blend in calibrated glass syringes using standard procedures (Menke & Steingass, 1988). The incubation was conducted in a water bath at 39°C in two independent runs. For each run, triplicates of each sample were incubated, and gas production volumes were measured at 3, 6, 12, 24, 48, 72, and 96 h to obtain six statistical repetitions. Each run contained two blanks, which were glass syringes containing only rumen liquor and buffer. The total gas values were corrected for blank incubation. To determine the fermentation kinetics, the corrected gas data were subjected to a curve-fitting statistics software programme called SigmaPlot (Microsoft Windows version 15.0) developed by SYSTAT Software Inc. The mathematical model of Orskov and McDonald (1979) was employed for fitting the curve as follows:

(2) $Y=b\left(1-e-ct\right)$(2)

where: Y = volume of gas produced at time t (ml)

b = potential gas production (mL/200 mgDM)

c = rate at which gas was produced from the insoluble fraction (mL/hr),

t = incubation time.

2.5. Digestibility and energy estimation

The Organic matter digestibility (OMD), metabolizable energy (ME), and net energy for lactation (NEL) were estimated according to the equations as follows Menke et al. (1979).

(3) $OMD,\mathrm{\%}=14.88+0.8893GP+0.448CP+0.651ash$(3)

(4) $ME,MJ/kgDM=2.20+0.136GP+0.057CP+0.002859EE2$(4)

(5) $NEL,MJ/kgDM=0.101GP+0.051CP+0.11EE$(5)

Where; GP = 24-h net gas production (ml/200 mg DM), CP = crude protein (%), and EE = ether extract (%).

2.6. Feed quality estimation

The feed quality was determined by estimating the dry matter intake (DMI), digestible dry matter (DDM), and relative feed value (RFV) using the following equations (Rohweder et al., 1978).

(6) $DMI,\mathrm{\%}LW=120/\left(NDF\mathrm{\%}\right)$(6)

(7) $DDM,\mathrm{\%}=188.9-\left(0.779xADF\mathrm{\%}\right)$(7)

(8) $RFV=\left(DMDxDMI\right)/1.29$(8)

2.7. Statistical analyses

Statistical analysis of all data was conducted using the GLM procedure of Minitab Statistical Software, version 19.0 (Minitab, LLC, NY, US, 2019). The experimental units were the plant species evaluated, with the chemical compositions (DM, OM, CP, CF, EE, NFE, ash, NDF, ADF, ADL), in vitro gas production and degradation parameters (a and b), and all other estimates of nutritional value (DDM, DMI, RFV, OMD, ME and NEL) serving as the response variables, and the plant species being the factors (fixed term). The three different sampling locations were used as statistical replications. For the in vitro gas production, six incubated samples for each plant species obtained from two independent runs were used as statistical replications (i.e., three replicated samples for each plant species for each separate run). Exponential curves were fitted to the replicated gas readings using Sigma Plot Statistical Software, version 14.0 (Systat Software Inc, 2017) based on the method described by Ørskovorskov and McDonald (1979). Mean comparisons were conducted using the Tukey method at a p < 0.05 significance level. Correlational analysis was performed using the Pearson Product-Moment Correlation add-on in the same version of the Minitab Statistical Software.

3. Results

3.1. Analytical chemical compositions of bamboo leaves and rice straws

Table 1 summarizes the analytical proximate compositions and detergent fiber fractions of the plant samples evaluated. The dry matter (DM) content was highest (P < 0.001) in the leaves of B. balcooa with a value at ~ 925 gkg⁻¹DM. The same plant species also recorded the highest (P = 0.004) ash content at ~ 179 gkg⁻¹DM. The leaves of O. abyssinica had the highest (P = 0.004) organic matter (OM) content at ~ 879 gkg⁻¹DM, and the highest (P < 0.01) crude protein (CP) content at ~128 g/kg DM. AGRA straw had the highest (P = 0.025) crude fiber (CF) content at ~ 283 gkg⁻¹DM, as well as the highest (P < 0.001) neutral detergent fiber (NDF) content at ~ 590 gkg⁻¹DM. On the other hand, AMANKWATIA straw had the highest (P < 0.001) acid detergent fiber (ADF) content at ~ 458 gkg⁻¹DM and acid detergent lignin (ADL) content at ~ 112 gkg⁻¹DM. All the plant materials had similar (P > 0.05) ether extract (EE).

Table 1. Analytical proximate compositions and detergent fibre fractions of bamboo leaves and rice straws

Compositions (gkg^−1 DM)
Plant Biomass	DM	OM	CP	CF	EE	ASH	NDF	ADF	ADL
^aBamboo leaves
O. abyssinica	918.00^a	879.30^a	128.00^a	269.00^ab	40.50^a	140.80^b	514.30^c	334.30^c	30.00^c
B. balcooa	924.70^a	842.00^b	104.80^b	273.20^a	44.30^a	179.00^a	522.00^c	355.00^c	51.00^b
^bStraws
AGRA	893.30^b	871.00^a	70.90^c	282.80^a	7.90^a	129.00^b	589.90^a	426.70^b	108.70^a
AMANKWATIA	872.30^c	834.80^b	66.80^c	227.20^b	14.40^a	165.20^a	578.80^b	457.70^a	112.00^a
SEM	0.507	0.631	0.902	0.828	0.564	0.631	0.959	1.690	1.2400
P-value	<0.001	0.004	<0.001	0.025	0.065	0.004	<0.001	<0.001	<0.001

Within column, parameters with similar superscripts (a, b, c) are not significantly different (p > 0.05). SEM = standard error of means.

DM=dry matter; OM = Organic matter; CP =crude protein; CF = crude fibre; EE =ether extract; ADF=acid detergent fibre; NDF = neutral detergent fibre; ADL = acid detergent lignin.

^aBamboo leaves = Bambusa balcooa (Beema), Oxytenanthera abyssinica (A. Rich.) Munro.

^bStraws =AGRA and AMANKWATIA rice varieties.

Figure 1 illustrates the comparative average nutrient pools for bamboo leaves and rice straws. On average, the bamboo leaves pooled the highest (P < 0.05) DM content at ~ 912 gkg-1DM, CP at ~ 125 gkg⁻¹DM, and EE at ~ 37 gkg⁻¹DM, while the rice straws had the highest (P < 0.05) pooled ADF at ~ 442 gkg⁻¹DM and ADL at ~ 110 gkg⁻¹DM. Nevertheless, both the bamboo leaves and rice straws had similar (P > 0.05) amounts of OM, CF, ash, and NDF.

Figure 1. Average proximate and fibre pools for bamboo leaves (Bambusa balcooa (Beema) and Oxytenanthera abyssinica (A. Rich.) Munro) and rice straws (AGRA and AMANKWATIA rice varieties). Data bars with similar superscripts (a, b) are not significantly different (p > 0.05.

DM=dry matter; OM = Organic matter; CP =crude protein; CF = crude fibre; EE =ether extract; ADF=acid detergent fibre; NDF = neutral detergent fibre; ADL = acid detergent lignin.

3.2. Feed quality indices and grading of bamboo leaves and rice straws

Table 2 presents estimates of dry matter intake (DMI), digestible dry matter (DDM), the relative feed value (RFV) and the quality scale for grading the bamboo leaves and rice straws. Among the plant materials analyzed, the leaves of O. abyssinica had the highest (P < 0.001) DDM estimated at ~ 87%, while that of B. balcooa recorded the highest (P < 0.001) DMI estimated at ~ 2.3%. In terms of quality, however, all the plant biomasses were graded as a feed with premium quality having RFV within the range 151–125 on the grading scale.

Table 2. Estimated forage quality indices for bamboo leaves and rice straws

Plant Biomass	DMI, % BW	DMD, %	RFV	*Forage Quality Grading
^aBamboo leaves
O. abyssinica	1.97^c	87.44^a	133.42^b	premium
B. balcooa	2.28^a	85.81^b	150.86^a	premium
^bStraws
AGRA	2.035^bc	80.44^c	126.86^b	premium
AMANKWATIA	2.073^b	80.17^c	128.86^b	premium
SEM	0.035	0.965	2.860
P-value	<0.001	<0.001	<0.001

Within column, parameters with similar superscripts (a, b, c) are not significantly different (p > 0.05). SEM = standard error of means.

DMI = dry matter intake; DMD = digestible dry matter; RFV = relative feed value;

*Quality Grading Standard assigned by The Hay Marketing Task Force of the American Forage and Grassland Council, the RFV were assessed as roughages based on prime >151; 1 (premium) = 151–125; 2 (good) = 124–103; 3 (fair) = 102–87; 4 (poor) = 86–75; 5(reject) < 75 (Rohweder et al., 1978).

^aBamboo = Bambusa balcooa (Beema), Oxytenanthera abyssinica (A. Rich.) Munro.

^bStraws =AGRA and AMANKWATIA rice varieties.

Comparatively, on average, the bamboo species pooled the highest (P < 0.05) DDM estimated at ~ 87% and RFV at ~ 141. Nonetheless, the average DMI was similar (P > 0.05) for all the plant biomasses analyzed (Figure 2).

Figure 2. Average relative quality indices of Bambusa balcooa (Beema) and Oxytenanthera abyssinica (A. Rich.) Munro and rice straws (AGRA and AMANKWATIA rice varieties). Data bars with similar superscripts (a, b) are not significantly different (p > 0.05); DMI (% BW) = dry matter intake; DDM (%) = digestible dry matter; RFV = relative feed value.

3.3. In vitro gas parameters, digestibility and energy estimates for bamboo leaves and rice straws

Table 3 shows a variable (P < 0.05) 96 h cumulative in vitro gas volumes, degradation kinetics, organic matter digestibility and energy estimates. Compared to the rice straws, both bamboo species produced higher (P < 0.05) 96 h gas production, with volumes ranging from ~ 9.5 to 10 mL compared to ~ 5.6 to 6.3 mL, and a higher insoluble (but fermentable over time) fraction, b at ~ 9.9 to 10.5 mL with a fermentation rate between 0.067 to 0.090 mLh⁻¹ compared to ~ 5.9 to 6.6 mL at a rate between 0.070 to 0.089 mLh⁻¹. Likewise, the leaves of the bamboo species had the highest (P < 0.05) estimates of organic matter digestibility (OMD), ranging from ~ 37 to 39%, metabolizable energy (ME) between ~ 3.9 to 4.0 MJ/kg DM, and net energy for lactation (NEL) between ~ 1.7 to 1.9 MJ/kg DM, compared to the rice straws, which recorded values of ~ 31 to 33%, 3.3 to 3.4 MJ/kg DM, and ~ 0.9 to 1.0 MJ/kg DM, respectively.

Table 3. Gas production (at 96 h in vitro incubation), degradation kinetics (b and c), calculated ME, NEL and OMD for bamboo leaves and rice straws

Plant Biomass	96 h	b	c	OMD	ME	NEL
^aBamboo leaves
O. abyssinica	10.16^a	10.53^a	0.067^b	36.55^ab	3.93^a	1.72^a
B. balcooa	9.50^a	9.96^a	0.090^ab	39.03^a	4.00^a	1.87^a
^bStraws
AGRA	6.27^b	6.38^b	0.070^ab	31.29^c	3.35^b	0.99^b
AMANKWATIA	5.64^b	5.94^b	0.089^a	33.32^bc	3.30^b	1.03^b
SEM	0.638	0.657	0.005	0.793	0.099	0.128
P-value	0.001	0.001	0.030	<0.001	<0.001	0.001

Within column, parameters with similar superscripts (a, b, c) are not significantly different (p > 0.05). SEM = standard error of means

96 h = 96-hour net gas production (mL/200 mg); b (ml)= insoluble (but with time fermentable) fraction; c = the gas production rate constant for the insoluble fraction (ml/h), OMD = organic matter digestibility (%), ME = metabolizable energy (MJ/kg DM), NEL = net energy lactation (MJ/kg DM).

^aBamboo leaves= Bambusa balcooa (Beema), Oxytenanthera abyssinica (A. Rich.) Munro;

^bStraws =AGRA and AMANKWATIA rice varieties.

Figure 3 shows the cumulative patterns of in vitro gas production from the bamboo and rice straws across the incubation hours.

Figure 3. Cumulative in vitro gas production (mL/200gdm) patterns for Bambusa balcooa (Beema) and Oxytenanthera abyssinica (A. Rich.) Munro and rice straws (AGRA and AMANKWATIA rice varieties). Data points (ml) are means of triplicates samples (n =3) per 200mgDM.

3.4. Correlational analyses of bamboo leaves and rice straws correlations

Table 4 shows the correlation between the nutrients and in vitro ruminal yields. CP contents of the plant materials strongly correlated positively with NDF (r = 0.092, p < 0.001), 96-h gas production (r = 0.897, p < 0.001), OMD (r = 0.722, p < 0.008), ME (r = 0.922, p < 0.001), NEL (r = 0.886, p < 0.001), and b (r = 0.881, p < 0.001). However, CP contents correlated negatively with ADF (r = −0.959, p < 0.001) and ADL (r = −0.977, p < 0.001). In addition, ADF strongly correlated negatively with OMD (r = −0.736, p < 0.006), ME (r = −0.992, p < 0.001), NEL (r = −0.866, p < 0.001), 96 h gas production (r = −0.895, p < 0.001), and b (r = −0.900, p < 0.001). Similarly, ADF strongly correlated negatively with OMD (r = −0.761, p < 0.006), ME (r = −0.948, p < 0.001), NEL (r = −0.866, p < 0.001), 96 h gas production (r = −0.952, p < 0.001), and b (r = −0.941, p < 0.001). Ash strongly correlated positively with the rate of fermentation, c (r = 0.731, p < 0.006). Furthermore, OMD strongly correlated positively with ME (r = 0.885, p < 0.001), NEL (r = 0.907, p < 0.001), 96 h gas production (r = 0.712, p < 0.006), and b (r = 0.757, p < 0.006). Likewise, ME strongly correlated positively with NEL (r = 0.974, p < 0.001), 96 h gas production (r = 0.824, p < 0.001), and b (r = 0.864, p < 0.001). Moreover, NEL strongly correlated positively with 96 h gas production (r = 0.909, p < 0.001) and b (r = 0.946, p < 0.006). The 96 h gas production strongly correlated positively with b (r = 0.981, p < 0.001) but strongly correlated negatively with c (r = 0.604, p < 0.007). Finally, the insoluble (but fermentable over time) fraction, b moderately correlated negatively with the rate constant, c (r = 0.582, p < 0.008).

Table 4. Pearson correlation coefficients (r) between nutrient compositions, in vitro net gas, and degradation kinetics

	CP	ASH	ADF	NDF	ADL	OMD	ME	NEL	96	b	c
ASH	−.118	-
ADF	−.959*	0.108	-
NDF	.092	−0.55	0.004	-
ADL	−.977*	0.090	0.955*	0.014	-
OMD	.722*	0.558	−0.736*	−0.425	−0.761*	-
ME	.922*	0.116	−0.929*	−0.238	−0.948*	0.885*	-
NEL	.886*	0.238	−0.866*	−0.274	−0.886*	0.907*	0.974*	-
96	.897*	−0.129	−0.895*	0.002	−0.952*	0.712*	0.909*	0.824*	-
b	.881*	−0.079	−0.900*	−0.145	−0.941*	0.757*	0.946*	0.864*	0.981*	-
c	−.536	0.731*	0.455	−0.385	0.536	0.006	−0.416	−0.331	−0.604*	−0.582*	-

*Significant (p < 0.05); NDF= Neutral detergent fibre, ADF=Acid detergent fibre; CP= Crude protein; ADL= Acid detergent lignin; 96 = 96-hour net gas production; b = insoluble (but with time fermentable) fraction; c = the gas production rate constant for the insoluble fraction, OMD = organic matter digestibility, ME = metabolizable energy, NEL = net energy lactation

4. Discussion

Chemical analysis and in vitro gas production analysis are fundamental tools in ruminant nutrition that enable scientists and practitioners to assess the quality of feedstuffs. Chemical analysis helps to identify the nutrient content of feeds while in vitro gas production analysis provides insights into the extent and rate of nutrient digestion in the rumen. Measuring feed dry matter (the weight of the feed minus the weight of the water) is critical in accurately determining the nutrient content of the feed, developing balanced diets, optimizing feed intake and digestion, improving palatability, and selecting the most cost-effective feed. It is an essential component of livestock feeding management that can have a significant impact on animal production and health. Protein (a measure of the total nitrogen content in the feed) is necessary for muscle development and milk production in ruminants. It is an essential component of the diet that supports the growth and repair of tissues and helps maintain proper metabolic functions. Ash provides inorganic minerals necessary for ruminant nutrition. Crude fiber is vital for roughage and proper digestive health. Ether extract provides energy for ruminant animals. Understanding these key nutrients and their importance in ruminant nutrition is crucial for formulating balanced and healthy diets for optimal animal growth and productivity. These analyses are crucial for formulating balanced ruminant diets that meet the nutritional requirements of animals and improve their health and productivity. By leveraging these techniques, producers can optimize feed utilization, reduce feed costs, and enhance the sustainability of their farming operations.

Largely, in this study, the nutritional characteristics of Bambusa balcooa (Beema) and Oxytenanthera abyssinica (A. Rich.) Munro differed from those reported in earlier studies for different bamboo species across various seasons (AFRIS, 2008; Poudyal, 1993; Sahoo et al., 2009; Antwi-Boasiako et al., 2011; Bhandari et al., 2015, Sasu et al., 2022; Sasu et al., 2023). This variation in nutritional characteristics may be attributed to several factors, such as the genetics of the bamboo species, edaphic conditions, and seasonal variations. It is worth suggesting that the nutritional content of bamboo leaves may fluctuate depending on the type, geographical location, and season of harvest. Therefore, ruminant nutritionists need to consider this nutritional variation when making appropriate adjustments in the inclusion of bamboo leaves in the diet to ensure optimal performance.

Despite this, the dry matter content of the bamboo leaves was comparable to that of tropical browses reported by Le Houerou (1980), the residual dry matter reported on old browsing herbs at the beginning of a new forage season by Onwuka (2007) and Babayemi and Adebayo (2020), as well as in tropical leguminous trees reported by Norton (1994), and the leaves and stems of Stylosanthes hemata reported by Attoh-Kotoku (2003). It must be emphasized; however, the dry matter content of the bamboo leaves was higher than what is expected for most fresh forages. This could be due to the dry season, which might have caused a reduction in moisture content and increased nutrient concentrations. While high dry matter content can be beneficial for ruminant nutrition, it is important to ensure that it does not lead to decreased palatability or limited nutrient availability, especially nitrogen (N). Thus, monitoring the quality and availability of bamboo leaves is crucial for proper ruminant nutrition. One of these quality characteristics of bamboo leaves is their N content as discussed in the next paragraph.

Dietary N can limit ruminant production if supply is insufficient relative to animal requirements (Pacheco & And& Waghorn, 2008). A chunk of N supply to the rumen microbes is of dietary origin which also represents the primary microbial biomass input to the ruminant animal (Pacheco & And& Waghorn, 2008; Waldo, 1968). It is important to realize that 70% or more of forage CP is degraded in the rumen, and the resulting ammonia is either used by rumen bacteria for their own growth (microbial crude protein, MCP) or absorbed into the blood stream. Once absorbed, the ammonia may be recycled or converted into urea and excreted, mainly in the urine (Pacheco & And& Waghorn, 2008). Therefore, poor N supply to the rumen can have negative effects on ruminant health and can result in poor animal performance, reduced growth rates, and lowered milk and meat production. More so, where quoted CP requirements represent a composite of the needs of the rumen microbes and the ruminant, the absolute CP requirement in the diet will change depending on the extent of utilization of N in the rumen vs. post-rumen (Pacheco & And& Waghorn, 2008). As reported, the minimum level of dietary crude protein (CP) required to supply adequate N for optimal rumen fermentative ability should be 100 gkg ⁻¹ DM (Bhandari et al., 2015; Babayemi & Adebayo, 2020; Norton, 1994). Expressed as N, the value is about 1.6 gkg ⁻¹ DM. The current range of CP values (~105–128 gkg ⁻¹ DM), expressed in N as ~ 1.7–2.0 gkg ⁻¹ DM reported for the leaves of the two-bamboo species were comparable with this threshold, suggesting that bamboo leaves could be a good source of dietary nitrogen (N) for ruminants, and their consumption can enhance the microbial activity in the rumen. Although, the reported values are consistent with the general observation for grass species, which characteristically contain lower CP (80–220 gkg ⁻¹ DM) compared with legume species (120–260 gkg ⁻¹ DM) (Ates, 2015), it is interesting to note that the CP content of the two-bamboo leaves align with the levels found in some protected forest range grass species (Poaceae sp.); Kentucky bluegrass, Smooth brome, Orchard grass, Red fescue, Sheep fescue, and Perennial ryegrass (Tenikecier & And& Ates, 2018), levels reported for olive leaves (Garcia et al., 2006; Olfaz et al., 2018), and the levels reported for tropical species used in grazing; Megathyrsus maximus, Cynodon spp., Cajanus cajan, Desmodium incanum, Stylosanthes macrocephala and Arachis pintoii (Tontini et al., 2019). Again, the bamboo leaves showed higher CP content compared to the mean levels found in leaf, stem, and whole fractions of four varieties of Cenchrus purpureus (Ansah et al., 2019).

The analytical characteristics of bamboo leaves in this study revealed high quantities of organic matter, crude fiber, crude ash, and ether extract, which is typical of ruminant feedstuffs. The current findings are consistent with those that have been published in our earlier studies for similar bamboo species in the same geographic area but across different seasons (Sasu et al., 2022; Sasu et al., 2023). The consistency in the quality attributes found between the current and the previous studies could be attributed to similarities in genetic make-up, sampling techniques, and analytical techniques used which may have overridden the seasonal effects. The fiber fractions (NDF, and ADF) of the leaves of these bamboos were found to be adequate enough to support the chewing ability of ingesting animals (Sasu et al., 2022; Sasu et al., 2023) than what was reported for Citrus aurantium leaves (Karabulut et al., 2007) but were similar to those published for most pasture forages (Mertens, 2015). The fibrous nature of bamboo leaves in synergy with their adequate ash (inorganic minerals), ether extract (fats), is a good indicator of feed of high quality required for efficient rumen environment in cattle, sheep, and goats to aid physiological functions such as bone development, enzyme activation, nerve and muscle function, Their organic matter content, on the other hand, is a good source of energy and protein for the microbes in the rumen, which then convert it into volatile fatty acids (VFAs) and microbial protein. These VFAs serve as the primary source of energy for ruminants and are crucial for maintaining the health and productivity of the animal, especially during the dry season when feed quality and quantity is uneven.

It is reported that in areas where rice straw is a readily available, it could provide a practical, and cheap source of low nitrogen but high fiber-containing fodder for feeding ruminants such as buffaloes, cattle, goats, and sheep (Aquino et al. (2020). Thus, livestock producers can easily haul and stack them to form reserve feed for their animals during lean months or when good-quality roughages are scarce. In the light of this, bamboo leaves could supplement rice straws in mix ration since the feeding of pure rice straw as a sole diet to ruminants during the stages of fast growth and early lactation has been shown to affect both body condition score and animal performance. This is due to lower CP content ranging between ~ 40 to 47 gkg-¹ DM (Aquino et al. (2020), ~ 30 to 70 gkg⁻¹DM (Gummert et al., 2020; Shen et al., 1998) high ash content ranging between ~ 108 to 130 gkg-¹ DM, NDF content ranging between ~ 700 to 730 gkg-¹ DM, ADF content ranging between ~ 398 to 435 gkg-¹ DM, and ADL content ranging between ~ 463 to 490 gkg-¹ DM (Shen et al., 1998). The range of CP values (~67 to 71 gkg-¹), NDF values (~579 to 590 gkg-¹), ADF values (~427 to 458 gkg-¹), ADL values (~109 to 112 gkg-¹) reported for the straws of improved rice varieties; AGRA and AMANKWATIA in the current study agree with the reported values. It is worth noting that the rice straws had slightly higher levels of neutral detergent fiber (NDF) and acid detergent fiber (ADF) compared to legume forages, which usually contain an average of 400 gkg⁻¹DM NDF and 350 gkg⁻¹DM ADF, according to Moore and Undersander (2002). As a result, AGRA and AMANKWATIA rice straws could provide excellent sources of fiber for ruminants especially cows, meeting the National Research Council (NRC) (2001) recommendation of 300 gkg-1DM NDF in their diet, with at least 210 gkg⁻¹DM NDF coming from forage sources. The nutritional values of barley, wheat, corn and oat were also investigated (Abaş et al., 2005). In these grains, CP ranged from ~ 93 to 12 gkg⁻¹DM, EE from ~ 17 to 45 gkg⁻¹DM, CF from ~ 41 to 117 gkg⁻¹DM. When compared with the range of values obtained for AGRA and AMANKWATIA rice straws, the differences especially between the values of CP were more evident. In the same study, the crude fiber values of grass hay and wheat straw were much higher (348 gkg⁻¹DM) than those reported for the two-rice straws but comparable to the data in the literature for hay (Lee et al., 2000; Seker, 2002).

Comparatively, the bamboo leaves outperformed rice straws in terms of dry matter and crude protein. Plant genetics, age, and growing conditions, such as soil and climate, can all contribute to this difference. As plants age, their crude protein content tends to decrease while their fiber content increases, affecting digestibility and nutrient availability. It should be noted that despite the differences in nutritional characteristics between the bamboo leaves and the rice straws, the study found that these plant materials can compare favorably to some of the promising ruminant feedstuffs documented in the literature, such as Stylosanthes hemata, cowpea haulms, and other tree fodders such as Grewia optiva, Morus alba, Celtis australis, and Grewia optiva (Antwi et al., 2004; Attoh-Kotoku, 2003; Singh et al., 1989). These comparisons with other feedstuffs documented in the literature suggest that the use of bamboo leaves and rice straws as alternative sources of feed for ruminant animals has the potential to provide a nutritionally balanced diet for optimal animal health and productivity.

However, digestibility plays an important role in ruminant nutrition since it reflects the proportion of nutrients that are available for absorption and utilization by the animal. In terms of fiber content, both bamboo leaves and rice straws can be classified as fibrous feeds of equal premium quality as graded according to Rohweder et al. (1978). This suggests that ruminants will consume them almost equally in a mixed ration. However, further comparative analysis revealed that bamboo leaves could provide relatively higher quality leaf biomass with higher digestible dry matter estimated at ~ 87% to the ingesting animals, compared to rice straws, estimated at around ~ 80%. This 7% difference in digestibility could be attributed to the relatively lower lignin and silica content of bamboo leaves, implying that bamboo leaves could provide a more efficient source of digestible nutrients for ruminants, improving their growth rates and reproductive performance while reducing levels of feed wastage, which would be beneficial for farmers.

Contrarily, high levels of lignification and silicification noted for rice straws may have contributed to their relatively lower estimate of digestible dry matter. Lignin is the most abundant natural aromatic organic polymer that plays a role in resisting compressing forces, providing protection against consumption by insects and mammals, and also inhibiting the rate and degree of microbial degradation (Aquino et al., 2020; Shen et al., 1998), and coupling with the presence of silica, the palatability and degradability of rice straws can be reduced in the rumen by preventing colonization by ruminal microorganisms, as explained by Iiyama et al. (1990) Bae et al. (1997), and Agbagla-Dohnani et al. (2003). Thus, treatment with a 4% urea solution could improve the straws and make them more digestible (Vadiveloo, 2000). More so, treating rice straw with calcium hydroxide or supplementing it with high protein feed can improve its intake, degradability, and milk yield compared to feeding untreated rice straw alone (Fadel Elseed et al., 2003; Wanapat et al., 2009). It can be inferred further that as rice straw is low in N and difficult to degrade, it is obvious that supplementation of a ration of rice straw with bamboo leaves will optimize rumen function, and also maximize utilization of the rice straw and increase intake. Chenost and Kayouli (1997) emphasized that it is primarily necessary to supply the rumen microorganisms with the nutritive elements needed for self-multiplication as well as for degradation of the cell walls of straw, leading to suitable conditions for the maintenance of good cellulolysis. Feeding only rice straw does not provide enough nutrients to the ruminants to maintain high production levels due to the low nutritive value of this highly lignified material. The high level of lignification and silicification coupled with low content of nitrogen as mentioned earlier has been found to strongly correlate with slow and limited ruminal degradation of the carbohydrates, affecting its value as feed for ruminants (Van Soest, 2006). This was observed in the current study. One important finding was the strong positive correlation between CP and the in vitro gas production, degradation kinetics as well as the estimated organic matter digestibility (OMD), metabolizable energy (ME) and net energy for lactation (NEL) values. In contrast, there was a strong negative correlation found between ADF and these parameters. This could explain the lower values of these parameters observed in the incubated substrates prepared from the AGRA and AMANKWATIA rice straws when compared to the leaves of Bambusa balcooa (Beema) and Oxytenanthera abyssinica (A. Rich.) Munro.

The current findings agree with the observation that rice straw is generally poorly fermented since it has low rates of disappearance in the rumen and low rates of passage through the rumen and hence lower gas production (Conrad, 1966). Gas is produced mainly when carbohydrates of the feedstuffs are fermented to short-chain fatty acids and the rate of gas production is associated with the rapid growth phase of microorganisms (Mauricio et al., 2001). Therefore, the higher gas produced from the incubated substrates prepared from the leaves of Bambusa balcooa (Beema), Oxytenanthera abyssinica (A. Rich.) Munro could be associated with their higher degradability in the rumen liquor than the AGRA and AMANKWATIA rice straws. The differences in the net gas production could also be related to the proportion of insoluble but degradable fermentable substrate which was relatively higher for the bamboo leaves than the straws. It must be emphasized that, collectively, the bamboo leaves and the straws produced lower net gas production and insoluble but degradable fractions than several forages analyzed in previous studies with net gas production values found between 12.38 and 52.54 ml/200 mg DM (Iantcheva et al., 1999; Getachew et al., 2002; Seker, 2002; Abaş et al. (2005). Again, when compared to some studies (Getachew et al., 2002; Krishnamoorthy et al., 1995; Umucalilar et al., 2002), the net gas production means of oat (50–55 ml/200 mg DM), barley (64–71 ml/200 mg DM), wheat (60–73 ml/200 mg DM) and corn (60–82 ml/200 mg DM) were in sharp contrast with the findings of this study. The differences in the net gas production between the current study and the previous ones could be attributed to the variable genetic makeup and proportions of fermentable fractions in the substrate of these feeds. Additionally, the degradability of the incubated bamboo leaves and rice straws substrates was measured at a fractional rate (c; h-1) with values comparable to the values observed for tall fescue and plantain (Burke, 2004) and perennial ryegrass (Chaves et al., 2006).

Lastly, the organic matter digestibility and energy contents of the bamboo leaves and rice straws were further investigated in this study by using their 24 h gas production values. The data showed that OMD, ME and NEL contents of the bamboo and straws were lower than wheat straw and alfalfa hay (NRC, 2001) but comparable to other studies that examined the same parameters (Iantcheva et al., 1999; Getachew et al., 2002; Seker, 2002; Abaş et al. (2005).

5. Conclusion

This study analyzed the potential of Bambusa balcooa (Beema) and Oxytenanthera abyssinica (A. Rich.) Munro leaves and AGRA and AMANKWATIA rice straws as alternative feed sources for ruminant animals. The analytical techniques used showed that these plant materials contain adequate fiber. It was revealed that on average terms, the bamboo leaves are superior in crude protein (N) concentrations, and leaf quality, which correlated strongly with their in vitro organic matter degradability, net gas production, fermentation rate and energy production making them a more promising alternative feed for ruminant animals.

The study emphasized that the potential high level of lignification and silicification, coupled with the low content of nitrogen in the rice straw accounted for the low protein content which strongly correlated positively with the observed slow and limited in vitro degradation of the incubating substrates prepared from the rice straws, thus, affecting gas production, fermentation rate and energy production. The study further confirmed that treating rice straw with urea or calcium hydroxide or supplementing it with high protein feed such as bamboo leaves can improve its intake, degradability, and animal productivity compared to feeding untreated rice straw alone. Furthermore, it is suggested that processing techniques such as chopping and pelleting should be considered to enhance the intake and digestibility of these plant biomasses.

However, a potential gap in this research is the lack of information on the practical application of these alternative feed sources in real-life farming scenarios. While the study provides valuable insights into the nutritional value and in vitro digestibility of these feed resources, there may be other factors such as availability, cost, and ease of use that could impact their feasibility and adoption by farmers. Future research could focus on evaluating the phytochemical (bioactive compounds) content, economic and practical aspects of using bamboo leaves, rice straws and other cereal straws such as wheat, maize, and millet straws as feed resources for ruminants, analyzing the in vivo cost-effectiveness, availability in different regions, and the best ways to process and incorporate them into animal diets.

Finally, further studies could examine the potential benefits of combining bamboo leaves and rice straws with different feed resources to create nutritionally balanced diets that optimize animal health and productivity while minimizing costs and resource use. Considering these aspects could provide more holistic insight into the feasibility and adoption of these alternative feed sources in ruminant nutrition.

Acknowledgments

The authors are grateful for the research materials provided by The International Network for Bamboo and Rattan (INBAR) and The Crop Research Institute (CRI) Division of The Centre for Scientific and Industrial Research (CSIR), Fumesua, Kumasi, Ghana.t

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The authors declare that they have no financial support from any organization or entirely about the content of the manuscript.

Notes on contributors

Prince Sasu

Prince Sasu is a researcher with a particular interest in sustainable livestock production and the utilization of underutilized feed resources. His research activities have focused on identifying and evaluating the nutritional characteristics of unconventional feed resources, particularly those suitable for ruminant livestock in the tropics. The research reported in this paper forms part of his PhD project, which aims to investigate the potential of bamboo leaves as a valuable and underutilized feed resource for livestock production in the region. By conducting a comparative nutritional evaluation of bamboo leaves and rice straws, the first author being the principal investigator and their team have contributed to the growing body of knowledge on the use of unconventional feed resources to improve livestock productivity and sustainability, while also addressing issues related to food security and poverty reduction in the region.

Notes

1. International Network of Bamboo and Rattan (INBAR) bamboo agroforestry cultivated in the Sekyere Central District of Ashanti Region, Ghana.

2. The Thomas ® Model 4 Wiley Mill. Made in the USA. Marketed and distributed by Onrion LLC. 93 South Railroad Avenue, STE C Bergenfield 07621–2352, New Jersey, USA

3. The ANKOM 2000 Automated Fiber Analyzer. Made in USA. Marketed and distributed by ANKOM Technology, Macedon NY 14,502, 2052 O’Neil Road.