JAHP_14_1_170-182

INTRODUCTION

Oil palm frond (OPF) is the major by-product of the industry (Ayyildiz et al., 2023), with 47-70% resulting from palm oil production (Shamsuddin et al., 2021). However, this biomass waste product can still be utilised for many purposes, including soil mulch and fertiliser (Moradi et al., 2012); bioethanol production (Broda et al., 2022); composite board material (Kuittinen et al., 2021); absorption material (Imsya et al., 2023); and animal feedstuff (Febrina et al., 2025). Nevertheless, its use as animal feed is constrained by its high fibre (70%) and lignin (22.90%) content; low metabolisable energy and protein content; and low dry matter digestibility (Astuti et al., 2020; Hamdon et al., 2020; Rusli et al., 2021). The nutritional content, digestibility, and palatability of oil palm fronds can be increased through the silage process (anaerobic) which is influenced by the availability of substrates to support microbial activity (Febrina et al., 2020).

The silage process provides many benefits including reduced dry matter loss (McDonald et al., 2002), increased lactic acid synthesis, production of silage with a pleasant aroma (Karnatam et al., 2023), reduced proportion of fibre fraction and cellulose crystallinity, and increased palatability, digestibility, and fermentation products (Febrina et al., 2020, 2025), reduced feed costs (Balehegn et al., 2022), lowered pH, and increased NH3 concentration and fermentation quality (Okoye et al., 2023). Improving feed quality will increase digestibility (Zhang et al., 2022) because it describes the nutrients that can be utilized by livestock to meet their needs, higher digestibility indicates better feed quality, because more feed can be utilized (Zewdie, 2019). These results are supported by previous researchers processing oil palm fronds into silage reduces the lignin content and increases the nutrient content and digestibility of OPF (Rusli et al., 2021; Saminathan et al., 2022); increases the production of volatile fatty acids (VFAs) and dry matter (DM) in vitro digestibility (Rahman et al., 2011; Rusli et al., 2019) reduces lignin content (Kumneadklang et al., 2019; Santoso et al., 2024).

In the silage process, the availability of precursors is a strategic factor to ensure its success, because it provides essential energy and protein for the growth and development of microbes and will affect the resulting silage product. Precursors that can be used in the silage process such as urea, poultry manure, buffalo faeces and empty oil palm bunch ash filtrate and rice husk ash filtrate. Urea provides nitrogen in the ammoniation process, which facilitates the cleavage of lignocellulose and lignohemicellulose bonds (New et al., 2021). This might be caused by the ability of urea to be quickly hydrolysed into ammonia, which, in turn, is synthesised by microbes into protein (Li et al., 2021). The use of urea in oil palm frond silage produces a crude protein content of 14.69% (Adli et al., 2022) and in oil palm stem pith silage produces a crude protein content of 13.27-15.67% (Febrina et al., 2025). However, the use of urea in OPF processing can pollute the environment (Chang et al., 2022). Therefore, the use of natural additives as a substitute for it is highly recommended. Filtrate of empty oil palm bunches ash and filtrate of rice husk ash are alkaline compounds, the mechanism is the same as urea (Rustamaji et al., 2022). Which can be used to loosen and break lignocellulose, lignohemicellulose and glycosidic bonds in the OPF fermentation process (Omar et al., 2021; Tahir et al., 2022). The inclusion of poultry manure (PM) in OPF fermentation provides urease to stimulate urea hydrolysis, resulting in fermented OPF with good physical quality) (Febrina et al., 2020) and lower lignin content (Febrina et al., 2018). In addition, buffalo rumen contains cellulolytic microbes which accelerate the decomposition of structural carbohydrates. Utilization of buffalo rumen as an additive in rape silage, produces a lignin degradation rate of 20.5% (Zhong et al., 2023).

In addition to being used as feed, oil palm frond silage also has the potential as an antimicrobial compound and its secondary metabolite content such as sterol and phenol in moderate amounts is needed by rumen microbes. This has been reported by previous researchers. Lactic acid bacteria from oil palm frond silage strain PDS 2 produced the highest inhibitory power, respectively, namely Aspergillus parasiticus FNCC 6033, Penicilium citrinum FNCC 6111 and Aspergillus flavus FNCC 6002 and can be used as an antifungal compound (Damayanti et al., 2015). Oil palm fronds contain bioactive steroids, tannins and phenolic compounds and can be developed as natural antimicrobials (Febrina et al., 2018, 2022); oil palm leaves have the potential as natural antibacterials and antibiofilms, economically and environmentally friendly (Nordin et al., 2023). In ruminants tannin and saponin function as defaunation agents and can protect feed protein from rumen microbial degradation (Kholif, 2023). The combination of tannin and saponin in feed can protect protein from rumen degradation, reduce NH3 concentration, methanogenic and methane bacterial activity in vitro (Jayanegara et al., 2020) and increase the digestibility of crude protein, NDF and ADF (Zhang et al., 2021).

Many studies have been conducted to improve the quality of oil palm frond silage, through the addition of safe and environmentally friendly additives but the results have not been optimal. Therefore, this study aims to find natural additives as a substitute for urea with the same function in the silage process and the content of bioactive compounds in oil palm frond silage that can support the growth and activity of rumen microbes so as to reduce environmental pollution and improve the nutritional quality of oil palm fronds. By assessing the synergistic effects of these natural additives, our goal is to improve silage production techniques and promote sustainable agricultural practices. Through a comprehensive understanding of the complex dynamics of the studied processes, we seek to provide practical insights into improving oil palm frond utilization and increasing feed efficiency.

MATERIALS AND METHODS

Study design and analyses

Palm fronds were obtained from an oil palm plantation in Kampar Regency, Riau Province, Indonesia. Leaf blades covering 2/3 of the front part of the petioles were used. A total of around 150-200 leaf blades was collected and cut into 3-5 cm pieces using a leaf chopper. The leaf cuts were then dried in the sun before being ground into leaf meal. Rice husks and empty bunches were burned, and the resulting ashes weighed. Two hundred grams of ashes were soaked in 1 liter of water for 24 hours before being filtered. The filtrate was collected and used in the fermentation process. Poultry manure (PM) was obtained from a chicken layer farm in Pekanbaru City, and buffalo faeces (BF) was taken from the buffalo farm of the Department of Animal Science of Universitas Islam Negeri Sultan Syarif Kasim.

Oil palm fronds silage (OPFS) was produced in the Nutrition and Feed Technology Laboratory, Universitas Islam Negeri Sultan Syarif Kasim Riau. Fresh oil palm fronds (OPF) cuts (1 kg) were mixed homogenously with additives poultry manure (PM), buffalo faeces (BF), empty bunch ash filtrate (EBAF) or rice husk ash filtrate (RHAF) at a level of 10% (dry matter basis). The mixture was then placed and compacted in silo bottles (laboratory-scale silos with a capacity of 1 kg). The silo bottles were closed tightly to create an anaerobic condition and then stored at a room temperature of 290C. After 21 days, the OPFS was taken out of the bottles and dried. The fibre fractions of OPFS were determined using the method developed by Van Soest et al. (1991).

The rumen fermentability of OPFS was measured using cow rumen liquid, in line with the method developed by Tilley and Terry (1963). Rumen liquid was obtained from a slaughterhouse in Padang City, West Sumatra. The liquid was strained through sterile fabric and the obtained supernatant was analysed for its pH, NH3 and VFA content. The precipitate was used for dry matter digestibility (DMD) and organic matter digestibility (OMD) analyses. A sample of dried OPFS (500 mg) was placed in a fermenter flask into which 10 ml rumen liquid and 40 ml McDougall buffer solution had been added. The flask was shaken by introducing a CO2 gas flow into the flask for 30 seconds (pH 6.5-6.9). The flask was tightly sealed with ventilated rubber and incubated in a water bath shaker at 39 oC. After 4 hours, the incubated sample was removed from the flask for determination of rumen pH, NH3, and total VFA content. Dry matter digestibility (DMD) and organic matter digestibility (OMD) determination was made on a sample incubated for 48 hours.

The identification of bioactive compounds was made on oil palm fronds silage (OPFS) extract which had been prepared based on the procedures used by Febrina et al. (2018). The OPFS was macerated in ethanol solution (96%) for 24 hours, with the maceration repeated eight times. Every 24 hours, the ethanol filtrate was separated, thickened using a vacuum evaporator, and weighed. Bioactive substances, including alkaloids, steroids, terpenoids, flavonoids, saponins, tannins and quinones, of the OPFS extract were identified using gas chromatography-mass spectrometry (GC-MS).

Statistical analysis

The study was conducted using a completely randomized design, with four treatments and five replicates. Treatments consisted of the use of natural additives including PM, BF, EBAF and RHAF. The data were subjected to an analysis of variance and a Duncan test (Petrie and Watson, 2013). Statistical analysis was performed using ANOVA at a significance level of 5%. Post-hoc comparisons between different treatments were conducted using Duncan’s multiple range test, also at a significance level of 5%. The data of rumen fermentability and nutrient digestibility were analyzed descriptively.

RESULTS AND DISCUSSION

The fibre fraction contents of OPFS are shown in Figure 1. The supplementation of natural additives had significant effects (P<0.01) on the content of the fraction. The highest lignin content (20.83%) was found in OPFS with the addition of BF. The addition of PM and RHAF in the oil palm frond silage process resulted in lower lignin content compared to the addition of buffalo faeces, 19.58% and 19.26%, respectively. The lowest lignin content was found in the treatment with the addition of EBAF, namely 18.56%.

The fermentability and in vitro nutrient digestibility of OPFS were indicated by certain measured parameters, as shown in Table 1. The rumen fermentability of pH (6.70-6.82); VFA (112.00-128 mM) and NH3 (12.40-15.50 mmol/L) were found to be in the normal range for microbial growth. Ammonia production in the rumen is influenced by the level of feed degradation and rumen pH. This shows that the level of feed degradation and rumen pH (Table 1) in OPFS with the addition of natural additives are not different so that the concentration of NH3 and rumen pH are also normal. Oil palm frond silage with the addition of poultry manure resulted in higher nutrient digestibility (51.92-65.28%) compared to the addition of other additives (Table 1). This is related to the activity of rumen microbes and their products, namely VFA and NH3 (Table 1). The high concentration of VFA (128 mM) and NH3 (15.50 mmol/L) in oil palm frond silage with the addition of poultry manure was followed by high nutrient digestibility. The bioactive compounds of OPFS in this study are listed in Table 2 and Figure 2. The steroid compound content in oil palm fronds fermented with natural additives ranges from 2.26-6.21% with the types of compounds including: stigmast-5-en-3ol (3 beta), stigmasterol, squalene, methylcholesterol, and ethylcholest-5-3. beta-ol (Table 2). It is shown that the largest component of organic compounds and phenol compound. Palmitic, lauric, stearic and monostearic acids formed the largest part of the organic compounds produced from POFS in all treatment groups.

Table 1: Rumen fermentability and in vitro nutrient digestibility of OPFS.

Parameters	Additives
Parameters	BF	EBAF	PM	RHAF
Rumen fermentability
VFA (mM)	112.00	117.50	128.00	120.00
NH3 (mmol/L)	12.40	13.40	15.50	14.30
pH	6.82	6.71	6.74	6.70
Nutrient digestibility (%)
Dry matter	58.91	58.30	62.47	60.32
Organic matter	61.52	60.25	63.83	61.39
Protein	62.27	61.09	65.28	62.52
Fibre	54.58	54.07	58.12	55.54
Ether extract	59.54	57.74	62.36	59.95
NFE	60.93	59.67	64.27	61.81
ADF	49.27	48.19	51.92	50.03
NDF	52.84	52.18	56.34	55.32
Cellulose	55.23	56.63	59.62	58.51
Hemicellulose	58.91	58.30	62.37	61.50

BF: buffalo faeces; EBAF: empty bunch ash filtrate; PM: poultry manure; RHAF: rice husk ash filtrate; VFA: volatile fatty acids; NFE: nitrogen-free extract; ADF: acid detergent fibre; NDF: neutral detergent fibre.

The low lignin content in OPFS with the addition of EBAF this might be related to the mineral content, especially potassium, that may affect the fibre (lignin) content. Potassium is known to play an important role in lignin hydrolysis (Medvedev et al., 2023). EBAF was found to have a higher potassium content (48.94%) (Novianti et al., 2015) than RHAF (5.58%) (Flores et al., 2021) or poultry manure (0.73-3.79%) (Palma, 2012; Tadele and Amha, 2015). The potassium content in RHAF (5.58%) which is almost the same as the potassium mineral content in PM (3.79%) causes the same lignin hydrolysis process so that the lignin content produced is also not different, 19.58% and 19.26%, respectively. The results of this study are almost the same as those reported by Febrina et al. (2020)

Table 2: Bioactive compounds of methanol extract of OPFS.

the addition of PM on oil palm frond silage process produces a lignin content of 19.94%.

The highest NDF, ADF and cellulose content was found in the OPFS treatment with the addition of EBAF as an additive source. NDF is a part of the cell wall that contains ADF, hemicellulose, cellulose and pentose. The high NDF content will be followed by high ADF, cellulose and hemicellulose content but low lignin content (Figure 1). The same thing was reported by Wang et al. (2021) and (Zhong et al., 2021), the NDF content is directly proportional to the ADF, cellulose and hemicellulose content but inversely proportional to the lignin content. In addition, the high content of potassium in EBAF loosens cellulose bonds, releasing lignin and hemicellulose, which eventually may reduce the fibre fraction content, resulting in the lowest lignin content (18.56%) which was significantly (P<0.01) lower than other treatments.

The released lignin will bind to alkalis, forming alkali-soluble lignin-alkalis (Ying et al., 2018), while the loss of lignin and hemicellulose causes a loose cellulose bond that makes it easier for the cellulase enzyme to hydrolyse cellulose into simple sugars (Zeng et al., 2014). The delignification process using alkaline compounds breaks hydrogen bonds (Chowdhury and Hamid, 2016) and stretches lignin away from cellulose and hemicellulose (Sukri et al., 2014). Pretreating corncobs with potassium solution in the form of 2% (w/v) of potassium permanganate alkaline solution (APP) within 6 hours at 50 °C resulted in the regaining of cellulose and hemicellulose by 94.56 and 81.47%, respectively, and the elimination of lignin from the corncobs by 46.79% (Ma et al., 2015).

Fermentability and nutrient digestibility of OPFS

pH plays a role in regulating various processes in the rumen, supporting microbial growth and producing products in the form of VFA and NH3 (Shen et al., 2023; Wang et al., 2023). Rumen pH is influenced by the production of saliva containing sodium bicarbonate which functions as a buffer to maintain the stability of rumen pH (Castillo-Lopez et al., 2021; Srivastava et al., 2021); as well as the concentration of VFA which is the end product of carbohydrate metabolism and NH3 is the end result of protein metabolism (Wang et al., 2022; Zhang et al., 2022). Carbohydrate fermentation was found to trigger a decrease in the pH of the rumen towards acid, while the fermentation of protein or NPN triggers an increase in the pH of the rumen towards the base (Hendawy et al., 2022). These figures were in line with the rumen pH values (6.86 to 6.92) of Bali cattle found by Afzalani et al. (2022). The pH value of the rumen is influenced by the type of feed, animal health, microflora and fauna of the rumen (Ali et al., 2020).

Treating OPFS with natural additives resulted in a rumen pH of 6.70–6.82. This shows that the addition of different additives to the oil palm frond silage process resulted in no different pH values. This showed that the rumen was in normal conditions, allowing rumen microbes to grow and develop suitably in order to perform the degradation process of OPFS. This is related to the availability of minerals, especially potassium minerals in EBAF and RHAF which are needed by rumen microbes for their growth and have a positive impact on the pH value and population of rumen microbes. Potassium plays an important role in cell metabolism as well as in the function of nerve and muscle cells (Wu, 2019). The addition of EBAF on oil palm pith silage produces a rumen pH of 6.78-6.80 (Febrina et al., 2025). Poultry manure contain the urease enzyme which can be utilized in the fermentation process, the addition of PM and urea to oil palm pith silage produces a rumen pH value of 6.76-6.80 (Febrina et al., 2025). Utilization of buffalo faeces as a source of inoculum in the fermentation of corn, soybean and corn straw produces a rumen pH (in vitro) of 6.5 (Cutrignelli et al., 2005). Thus, this confirms and supports previous researchers that the addition of natural additives to the oil palm frond silage process produces normal rumen pH values that can support microbial growth and activity.

The use of natural additives was found to produce OPFS with rumen NH3 concentrations of 12.4–15.5 mmol/L, figures within the normal range of rumen NH3 (6-21 mmol/L) for microbial growth (McDonald et al., 2002). Ammonia is a result of protein metabolism that is broken down into amino acids. Oil palm frond silage with the addition of buffalo faeces produces 12.40 mmol/L of NH3, lower than the addition of other additives. The low concentration of NH3 in this treatment is thought to be related to the number and activity of cellulolytic microbes in BF which have decreased and are unable to survive in aerobic conditions and the activity of microbes in buffalo faeces is lower than in buffalo rumen fluid. Microbial activity in faeces is lower than rumen microbial activity (Lourenco et al., 2020). Syapura et al. (2013) reported that straw fermented with the addition of buffalo faeces produced an N-NH3 concentration of 4.66–6.86 mM.

Oil palm frond silage with the addition of PM produced an ammonia concentration of 15.50 mmol/L, higher than other treatments. The high concentration of ammonia in this treatment is thought to be related to the high crude protein content in PM. This is in accordance with what was conveyed by Lopes et al. (2020) that the rumen NH3 concentration is influenced by the crude protein content. Kopeć et al. (2018) stated that PM contain 5% nitrogen; 3.9% phosphorus and 2.4% potassium. Potassium plays a role in carbohydrate metabolism and is a cofactor in protein synthesis; phosphorus is a component of adenosine triphosphate (ATP) and nucleic acids (Baj et al., 2020) which can be utilized by microbes for their growth and feed degradation processes. Poultry manure are also a source of urease enzymes so that they can accelerate the breakdown of urea into ammonia, resulting in higher NH3 concentrations. This might be attributable to the notion that poultry manure contains urease enzyme (Yin et al., 2021), true protein and non-protein nitrogen in the form of rumen degradable uric acid (Tadele and Amha, 2015; Zurak et al., 2023).

VFA is a result of carbohydrate metabolism which functions as an energy source for microbes (Liu et al., 2021). In this study, the total production of VFA (112–128 mM) was within the normal range of rumen VFA of 70-150 mM (McDonald et al., 2002). These results suggest that the process of carbohydrate metabolism inside the rumen was progressing appropriately. Suitable rumen environmental conditions, as indicated by rumen pH, rumen NH3 concentration, and rumen VFA content are important for supporting the optimal growth of rumen microbes (Xia et al., 2018). The highest VFA concentration was found in oil palm frond silage with the addition of poultry manure as an inoculum source in line with the high concentration of NH3 (Table 1). This shows a positive correlation between VFA and NH3. The availability of energy (VFA) will be used by rumen microbes as a carbon source for the formation of microbial proteins. This result is in line with Makmur et al. (2020) that increasing NH3 concentration will increase VFA concentration.

The nutrient digestibility of oil palm frond silage with the addition of natural additives was 48.19-65.28% (Table 1), this value is in line with that reported by Safira et al. (2024) in vitro digestibility of dry matter and organic matter of oil palm frond silage were 61.96% and 60.91% respectively and Mulianda et al. (2018) the digestibility of dry matter and organic matter of oil palm frond silage fermented with local microorganisms (MOL) was 64.88% and 65.8%. This value is higher than that reported by Santoso et al. (2024) rations made from oil palm frond silage produced in vitro digestibility of dry matter of 44.7-57.7%; organic matter 43.7-54.7% and NDF 24.8-35.7%.

Volatile fatty acid is the result of carbohydrate metabolism that functions as an energy source for microbes and NH3 is the result of protein metabolism needed by microbes for their growth. When energy and protein sources are available in optimal amounts, microbes will grow and develop well and produce enzymes to degrade feed, resulting in high nutrient digestibility. This shows the beneficial effects of protein-energy synchronization that can increase microbial activity and their ability to digest feed. High nutrient digestibility increases ruminant productivity, because nutrients can be utilized optimally (Sharif et al., 2019). The results of this study confirm Febrina et al. (2025) complete growth precursors (urea, molasses and EM) in oil palm stem pith silage, producing the highest concentration of VFA, NH3 and nutrient digestibility and Putri et al. (2021), a balance of 14% protein and 70% energy (TDN) produces the highest VFA, NH3, microbial protein synthesis and nutrient digestibility. The addition of 10% poultry manure to baggage silage was found to lower NDF content and increase ash content and the digestibility of dry matter and organic matter in vitro (Shitandi et al., 2009).

Oil palm frond silage with the addition of buffalo faeces and empty oil palm bunch ash filtrate resulted in lower nutrient digestibility (compared to the addition of other additives) (Table 1). This is thought to be related to the low microbial activity in buffalo faeces compared to buffalo rumen. The microbial population in buffalo faeces is lower and has not been able to compete with microbial activity in buffalo rumen (Agarwal et al., 2020; Chiaravalli et al., 2019; Marlina et al., 2020). Buffalo faeces have been used as inoculum to increase the nutrient digestibility of rice straw (Syapura et al., 2013) and tofu dregs (Bidura et al., 2014). It is suggested that this was related to the dominant fibrolytic enzyme found in the buffalo rumen (Sujani and Seresinhe, 2015), an enzyme which is able to break down lignocellulose and lignohemicellulose bonds (Sio et al., 2022).

The bioactive compounds of OPFS

Partial pyrolysis of cellulose and hemicellulose resulted in the production of organic compounds. Palmitic acid, together with oleic, linoleic and stearic acids, are also the most dominant organic compounds found in palm oil (Ping and Yusof, 2009; Simeh, 2004) and oil palm leaves (Islam et al., 2021). Palmitic acid is a group of fatty acids with non-polar poles that are the same as gram-negative bacteria so that it can penetrate the cell walls of gram-negative bacteria (Gagat et al., 2024). The antimicrobial properties of palmitic acid might be attributed to its ability to damage membrane permeability and ion partition on cell membranes, causing cell lysis (Agoramoorthy et al., 2007; Al-Shammari et al., 2012; Langner and Hui, 2000; Mikut et al., 2016). The results of this study indicate that the organic acid content (palmitate, laurate, stearate) in oil palm fronds can be used as a natural antimicrobial while confirming previous researchers that the combination of palmitic acid and lauric acid effectively inhibits S. aureus and E. coli. and reduces dependence on chemical disinfectants (Auttajinda et al., 2023).

Phenol is the second largest compound after organic compounds, which is produced from the fermentation of oil palm fronds with the addition of natural additives (6.93-11.93%). Phenol is a bioactive compound that functions as an antimicrobial through the process of denaturing bacterial cell proteins and precipitating proteins in bacterial cells so that bacterial cell metabolism is inhibited. Phenolic compounds can capture free radicals and inhibit the growth of pathogenic microbes (Ali et al., 2020; Mohamad Said et al., 2021). This is in accordance with what was reported by Febrina et al. (2018) that the tannin and steroid content in oil palm fronds can inhibit the growth of Staphylococcus aureus and Escherichia coli. The phenol content in oil palm fronds also functions as an antioxidant that can capture free radicals. The results of this study confirm the research of Imsya et al. (2013) phenolic compounds in oil palm fronds fermented with Phanerochaete chrysosporium showed antioxidant activity with an incubation time of 10 days; and Hussin et al. (2015) oil palm fronds can be used as a source of green antioxidants to inhibit mild steel corrosion.

Steroids in plants have activities as anticholesterol and anticancer (Mendoza et al., 2025). Stigmasterol is a sterol compound that has anticholesterol properties, through the mechanism of inhibiting cholesterol absorption in the intestine, inhibiting the development of colon cancer and suppressing cholesterol in the liver (Li et al., 2022). Under stressful conditions, stigmast-5-en-3ol (3. beta.) can boost the body’s immune system (Madhubala and Santhi, 2019). Zain et al. (2022) reported that providing complete rations made from ammoniated oil palm fronds supplemented with direct-fed microbial (DFM) and virgin coconut oil (VCO) to Bali cattle had a very significant effect (p<0.05) in reducing cholesterol levels, LDL and increasing HDL in the blood of Bali cattle. The same thing was reported by Febrina et al. (2020) that providing fermented oil palm fronds in kacang goat rations significantly reduced blood cholesterol levels.

Inositol compounds, which possibly include inositol (vitamin B8) and B-complex vitamins (Bizzarri et al., 2014), were found in FPOF treated with natural additives. Inositol plays a role in the transduction of hormone and neurotransmitter signals, regulating the insulin hormone and forming cell structures and antidiabetic compounds through the glycosylation inhibition process known as AGEs (Advanced Glycation End Products) (Nie and Cooper, 2021). Vitamin B complex functions as an enzyme cofactor for energy formation, protein and lipid metabolism (Hrubša et al., 2022) so it is very necessary for rumen microbes for their growth and development (González-Montaña et al., 2020). In ruminant livestock, Vitamin B complex does not need to be added to the ration because of the ability of rumen microbes to synthesize it, thus the use of oil palm frond silage can fulfill the need for Vitamin B complex and its inositol content can be developed as an antidiabetic compound. Febrina et al. (2021) reported that the provision of oil palm fronds fermented with Phanerochaete chrysosporium in Kacang goat rations significantly increased ration consumption, body weight gain, and ration efficiency, and Suyitman et al. (2020) reported that the provision of ammoniated oil palm fronds supplemented with minerals in Simmental cattle rations significantly increased ration consumption, body weight gain, and ration efficiency.

Vitamin E (alpha tocopherols) was found in FPOF in all treatment groups, consisting of alpha tocopherol (2-3.9%) and sterols/steroids (2.26-6.21%). Vitamin E is a lipophilic antioxidant formed from four tocopherol molecules and four tocotrienol molecules (Munoz and Bosch, 2019). Vitamin E is able to suppress lipid peroxidation in cell membranes so that the integrity of the cell membrane is maintained to maintain the cell metabolism process (Rizvi et al., 2014). The antioxidant can react with free radicals, protect lipids from peroxidation, stabilise membrane structures, act as a body system, and avoid oxidative stress (Agarwal et al., 2014). Previous researchers reported the positive effects of adding vitamin E to rations in cattle which can increase immunity and antioxidative stress (Sordillo, 2016) and relieved inflammatory responses and prevent mastitis (Xiao et al., 2021). Jamarun et al. (2020) reported that providing rations made from ammoniated oil palm fronds, Titonia and Elephant Grass to Etawa crossbred dairy goats increased the concentration of Ca and P minerals in milk, but did not affect the levels of protein, fat and lactose in milk.

CONCLUSION AND RECOMENDATIONS

OPFS treated with natural additives was found to have nutrient digestibility (in vitro) and normal rumen fermentability conditions (pH, VFA and NH3) to support microbial growth. The inclusion of natural additives in the fermentation of palm fronds resulted in OPFS possessing bioactive compounds including organic, phenols, steroids, furans, vomifoliol, palmitic acid, flavonoids and quinones. The results of the study have revealed new information on treatments that can be given to oil palm fronds to improve their digestibility. Secondary metabolites contained in OPFS deserve to be further studied for their utilisation as feed additive materials, as they contain certain antimicrobial and antioxidative properties.

ACKNOWLEDGEMENT

Funding assistance from the Institute for Research and Community Service of Universitas Islam Negeri Sultan Syarif Kasim Riau with a contract No. 0600/R/2020 in the Applied Cluster of National Strategic Studies for the fiscal year 2020 was acknowledged.

NOVELTY STATEMENT

The use of natural additives (poultry manure; buffalo faeces; empty bunch ash filtrate/EBAF; and rice husk ash filtrate/RHAF as a substitute for urea with the same function in the silage process and the content of bioactive compounds in oil palm frond silage that can support the growth and activity of rumen microbes so as to reduce environmental pollution and improve the nutritional quality of oil palm fronds.

AUTHOR’S CONTRIBUTIONS

DW, RF, RP, NQ format analysis; JJ, SIZ visualization; NQ, SS, SIZ writing-review & editing; DW conceptualization; DW, SS, NR supervision; RF, NR, JJ data curation, RR methodology; NQ, DW, RR writing-original draft, DW project-administration; SS, RP resources; SIZ software; JJ, RF, NR validation

Ethical approval

This research was conducted based on ethical clearance by Faculty of Agriculture and Animal Sciences, Universitas Islam Negeri Sultan Syarif Kasim Riau–Indonesia (No: KEP.FPP/10/09/2021).

Generative AI and AI-assisted technology statement

The authors used generative AI tools only for language refinement, and they take full responsibility for the accuracy and integrity of the manuscript’s scientific content.

Conflict of interest

The authors have declared no conflict of interest.

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