Nutrient content and digestibility of silage made from mixed oil palm fronds and tofu waste

Muhammad Ridla^1,2, Mulyanto³, Muhammad Agus Setiana^1,2 and Nahrowi^1,2

¹ Departmen of Nutrition and Feed Technology, Faculty of Animal Science, IPB University, Kampus Dramaga, Bogor 16680, Indonesia
hmridla@apps.ipb.ac.id
² Center for Tropical Animal Studies (CENTRAS), IPB University, Kampus IPB Baranangsiang, Jl. Raya Pajajaran, Bogor 16153, Indonesia
³ Study Program of Nutrition and Feed Technology, Faculty of Animal Science, IPB University, Kampus Dramaga, Bogor 16680, Indonesia

Abstract

Alternative feed sources, such as agricultural plantations or industrial by-products, can be viable options for foraging. However, their limited nutrient content can hinder their utilization. Silage production, on the other hand, can improve its nutritional quality by mixing high-moisture agricultural by-products with varying nutrient contents and preserving them. This study aimed to determine the optimal level of tofu waste addition to oil palm frond silage to improve fermentation quality, nutritional value, and digestibility. The silage was produced by mixing oil palm fronds (OPF) and tofu waste (Tw) in predetermined proportions for each treatment: Tw0 (100% OPF + 0% Tw), Tw10 (90% OPF + 10% Tw), Tw20 (80% OPF + 20% Tw), Tw30 (70% OPF + 30% Tw), and Tw40 (60% OPF + 40% Tw). The study measured dry matter, crude protein, NDF, ADF, in vitro dry matter digestibility, and organic matter digestibility. The experimental design used a Completely Randomized Design (CRD) with five treatments and three replications. Data were analyzed using Analysis of Variance (ANOVA) followed by Duncan's multiple-range test if significant. The results showed that silages produced from mixed oil palm fronds and tofu waste had a low pH, indicating good fermentation, improved nutrient content, and silage digestibility. These findings suggest that adding tofu waste could be a valuable option in silage production to enhance forage quality for ruminant feed.

Keywords: agricultural, by-products, high-moisture, mixing, preserving

Introduction

Livestock farming, particularly for ruminants, is growing in Indonesia. However, limited forage production makes it challenging to provide cheap and accessible feed. The primary source of feed is local forage, with only a small amount coming from cultivated forage. To address this, agricultural by-products can be a viable alternative, but their limited nutrient content is a hindrance. Various technologies are needed to improve their nutritional quality, including mixing and preserving them as silage (Nascimento et al 2023).

One significant challenge in processing feed from waste is its high moisture content, making it difficult to store and use directly. While drying technology has been commonly used, it has limitations in terms of the amount of material that can be dried in a specific period and place, making it challenging to apply to large quantities of waste (Lendrawati et al 2012).

To address the high moisture content in agricultural by-products, they can be converted into silage through lactic acid bacteria fermentation, which typically has a high moisture content (McDonald et al 1991). Mixing agricultural by-products with high moisture and various nutrient content and preserving them as silage can reduce the problem of high moisture waste while also producing valuable animal feed (Ridla and Uchida 1994).

Ruminants require forage as a source of fiber for rumen health and concentrate as a source of nutrients to support growth or production. In the area around oil palm plantations in Indonesia, agricultural by-products such as oil palm fronds as a fiber source and tofu waste as a concentrated protein source could be mixed and conserved as silage, becoming valuable ruminant feed for rural livestock development.

This study aims to determine the optimal level of adding tofu waste to oil palm frond silage to improve the fermentation quality, nutritional value, and digestibility of the silage.

Materials and methods

The oil palm fronds used in this study were obtained from the experimental station of IPB University in Bogor, Indonesia. Mature and intact palm fronds were separated from their petioles, cut into 2 cm pieces, and air-dried for 12 hours. The wet tofu waste used had a moisture content of 84.47%. The nutrient composition of the palm fronds and tofu waste can be found in Table 1.

Silage production

To produce the silage, oil palm fronds (OPF) and tofu waste (Tw) were mixed in predetermined proportions based on the treatment. Five treatments were applied: Tw0: 100% OPF + 0% Tw, Tw10: 90% OPF + 10% Tw, Tw20: 80% OPF + 20% Tw, Tw30: 70% OPF + 30% Tw, and Tw40: 60% OPF + 40% Tw.

The mixture of materials was then placed into a 1-liter plastic bottle silo and compacted to minimize the air content inside. All the silos were closed and wrapped with tape to achieve anaerobic conditions. Before being stored for 6 weeks at room temperature, samples from all silos were weighed and labeled with their corresponding treatment.

After 6 weeks, the silo containing the silage was weighed and opened. Each sample was divided into two parts. Some samples were extracted using distilled water with a dilution of 10 times to measure the pH, while the remaining samples were dried using an oven method. The dried silage was weighed and 300 grams of it were taken for further analysis.

Chemical content and digestibility analysis

The dry matter (DM), crude ash (CA), crude protein (CP), ether extract (EE), and non-fiber carbohydrate (NFC) content using AOAC (2015) method. Neutral detergent fiber (NDF) and acid detergent fiber (ADF) were measured using the Van Soest et al (1991) method. The in vitro dry matter digestibility (IVDMD) and organic matter digestibility (IVOMD) were also analyzed using the Tilley and Terry (1963) method.

Research design

The experimental design used was a Completely Randomized Design (CRD) with five treatments and three replications. The research results were analyzed using Analysis of Variance (ANOVA), followed by Duncan's multiple range test if the differences among treatment means were statistically significant at the 0.05 level (p<0.05).

Results and discussion

The results of this study indicate that the addition of tofu waste had a positive impact (p<0.05) on fermentation quality and nutrient parameters of the silage, including pH, crude protein, NDF, ADF, IVDMD, and IVOMD (Table 2).

Silage dry matter content

As the amount of tofu waste increased, there was a decrease (p<0.05) in the percentage of dry matter in the silages. This decrease in dry matter content could be attributed to the high moisture content of tofu waste. In this experiment, the dry matter content of the silage ranged from 31.33% to 56.95%. Previous studies have suggested that the ideal range for dry matter content for good silage fermentation is between 25% and 35% (Jensen et al 2005).

Dry matter contents that are too low can lead to the growth of clostridia bacteria, while overly high dry matter contents can inhibit the activity of lactic acid bacteria (Kung et al 2018). In this study, the dry matter content was higher than the recommended range for silage making, likely due to the high initial dry matter content of the palm front (56.01%). However, the addition of tofu waste reduced the dry matter content to almost an ideal range and improved the quality of the silage fermentation.

Figure 1. Effect DM content, % of replacing OPF with tofu waste

Silage pH value

The addition of tofu waste had a significant effect (p<0.05) on the pH value of the silage. The silage pH values ranged from 4.14 to 4.47, within the recommended range for good fermentation. This suggests that adding tofu waste could support the activity of lactic acid bacteria during fermentation, which contributed to the decrease in pH of the silage mixture of oil palm frond and tofu waste.

Figure 2. Effect pH value, % of replacing OPF with tofu waste

To ensure good anaerobic fermentation, fibrous materials require sufficient populations of LAB and easily fermentable carbohydrate substrates. In this study, tofu waste was used as a source of carbohydrates. The pH is a reliable indicator of silage quality. McDonald et al (1991) suggested that a pH beTween 3.5 and 4.2 is desirable. The low pH value of the silage was achieved due to the availability of carbohydrates, which stimulated the growth of lactic acid bacteria and led to the formation of an acidic environment. Tofu waste provided an easily available energy source that facilitated the formation of an acidic atmosphere. In a previous study by Ridla and Uchida (1994), the mixture silage of barley straw and wet brewers’ grain was reported to have pH values ranging from 5.5 to 3.9.

Silage crude protein content

In the study, the crude protein content of mixed palm frond-tofu waste silages increased (p<0.05) as the level of tofu waste was increased. The highest crude protein content was observed at the 40% level of addition (Tw40), with the crude protein content ranging from the lowest value of 7.74% (Tw0) to the highest value of 14.98% (Tw40). The increase in crude protein content up to the addition of 40% tofu waste indicated a significant contribution of tofu waste to the crude protein content. This suggests that tofu waste could be an effective source of protein in ruminant diets.

Figure 3. Effect CP content, % of replacing OPF with tofu waste

The resulting silages' crude protein contents were within the range of crude protein contents of some tropical grass types, as reported by Evitayani et al (2005), with values ranging from 6.6 to 16.2% (DM). Ridla and Uchida (1994) confirmed that the addition of brewer's grain increased the crude protein content of barley straw-wet brewer's grain silage from 2.46 to 23.95%. The crude protein contents of the resulting silages appeared to meet the standards set by the National Indonesian Standard No. 3148.2 2009 (SNI 2009) for use in ruminant rations, specifically for beef rations, including fattening, mother cow, and bull. The standards require a minimum crude protein content of 13%, 14%, and 12%, respectively.

Silage NDF and ADF content

Neutral detergent fiber (NDF) is a measure of the cell wall content in forage and is an important indicator of forage quality. The results show that the NDF content of the silages decreased (p<0.05) with the addition of tofu waste, from 74.38% in the control group (Tw0) to 68.47% in the group with the highest level of tofu waste addition (Tw40). The decrease in NDF content could be attributed to the lower NDF content in the tofu waste used as an additive.

Figure 4. Effect NDF content, % of replacing OPF with tofu waste	Figure 5. Effect ADF content, % of replacing OPF with tofu waste

Acid detergent fiber (ADF) is an important indicator of the lignin and cellulose content in forage. The results show that the ADF content of the silages decreased (p<0.05) with the addition of tofu waste, from 55.60% in the control group (Tw0) to 44.63% in the group with the highest level of tofu waste addition (Tw40). The decrease in ADF content might be due to the addition of the lower ADF content in the tofu waste.

The decrease in the contents of NDF and ADF of silages with the addition of agro-industrial byproducts has been reported by Rusdy (2016). Additionally, Ridla and Uchida (1994) found that the NDF and ADF content of barley straw-wet brewer's grain silage decreased from 77.98% to 54.29% and from 56.45% to 35.65%, respectively, as a result of wet brewer's grain addition.

Silage digestibility

In vitro dry matter digestibility (IVDMD) and in vitro organic matter digestibility (IVOMD) are measures of forage digestibility. The results showed that the addition of tofu waste had a significant effect on both IVDMD and IVOMD. Specifically, the IVDMD increased from 50.17% in the control group (Tw0) to 62.35% in the group with the highest level of tofu waste addition (Tw40), and the IVOMD increased from 49.42% in the control group (Tw0) to 62.07% in the group with the highest level of tofu waste addition (Tw40).

Figure 6. Effect DM digestibility, % of replacing OPF with tofu waste	Figure 7. Effect OM digestibility, % of replacing OPF with tofu waste

The increase in IVDMD and IVOMD could be attributed to the high protein content and low fiber content of tofu waste. Tofu waste had a high protein content, which was easily degraded by microorganisms during the rumen fermentation process, leading to an increase in available nitrogen content. This, in turn, enhances the digestion process by microorganisms responsible for the fermentation process during rumen fermentation and digestion. The low fiber content of tofu waste was also a contributing factor to the increase in IVDMD and IVOMD. The decrease in fiber content could be attributed to the low neutral detergent fiber (NDF) and acid detergent fiber (ADF) content of tofu waste, resulting in a decrease in the fiber content of the silage with the addition of tofu waste. The lower fiber content could make the silage more easily digestible, resulting in a higher IVDMD and IVOMD.

Ali et al (2023) reported that the IVDMD and IVOMD of a mixture of oil palm frond and Indigofera zollingeriana feed pellets increased from 47.7% and 46.9% to 57.4% and 56.4%, respectively, due to the addition of Indigofera zollingeriana from 0% to 45%. The results of silage digestibility suggest that a mixture of palm frond and tofu waste silage could be a viable option for farmers in Indonesia looking to feed their livestock with high-quality and nutritious feed. However, further testing and analysis might be necessary to determine the full nutritional value and suitability of the silage for specific livestock.

Photo 1. Oil palm frond, tofu waste, and a mixture of both

Conclusions

• Adding tofu waste to the forage during the ensiling process positively affects silage preservation by lowering its pH value, indicating good preservation.
  
  
• Including tofu waste improves the nutrient content and digestibility of silage, potentially enhancing the utilization of palm fronds for ruminant feed.
  
  
• These results suggest that tofu waste could be a valuable additive in silage production to improve the quality of forage.
  
  
• Further in vivo studies are needed to confirm the effect of mixed silage on livestock health and production efficiency.

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