The substitution of sweet potatoes (Ipomoea batatas) plant waste as indigenous forage replacement for goat feeding in the limestone mining area

Doso Sarwanto¹, Sari Eko Tuswati¹ and Caribu Hadi Prayitno²

¹ Faculty of Animal Science, Wijaya Kusuma University, Purwokerto, Central Java, Indonesia
dososarwanto@gmail.com
² Faculty of Animal Science, Jenderal Soedirman University, Purwokerto, Central Java, Indonesia

Abstract

This study aims to assess the use of sweet potato waste as a substitute for indigenous forage for goat feed in the limestone mining area. This study measured four parameters, namely feed consumption, dry matter consumption, dry matter digestibility, and the average daily weight of goats. The samples used were 16 male Kacang goats with an average body weight of 16.1 ± 0.93 kg. The study employed an experimental method with a complete randomized design, 4 treatments (sweet potato waste level treatment: 0%, 10%, 20%, and 30%), and 4 replications. The results showed that the treatment had no significant effect on the feed consumption or dry matter consumption (p> 0.05), but strongly influenced the digestibility of dry matter and organic matter (p< 0.01). Sweet potato plant waste produced from former limestone mining land can replace indigenous forage in limestone mountains for as much as 30% of the total forage feeding of goats.

Keywords: forage, goat, limestone, sweet potato, waste

Introduction

Demand for livestock products, particularly meat, is always rising in tandem with changes in dietary habits, economic levels, and population growth. However, because of the depletion of water and land resources as well as climate change, there is a negative trend in the expansion of meat production (Escarcha et al 2018). Nevertheless, one of the most significant effects of climate change is the alteration of ecosystems, which will lower cattle productivity. These days, compared to crops and other fields, the detrimental effects of climate change on the livestock industry have not received as much attention (Escarcha et al 2018; Kantenen et al 2018).

Stretching from Sumatra to Papua, the limestone mountains of Indonesia span 15.4 million hectares. Limestone mountains are landscapes that have important environmental values such as water resources, biodiversity, and tourism. Because limestone mountains are utilized so extensively for building materials and cement production, they serve a particularly strategic purpose. Thus, in keeping with Indonesia's rate of development, the community has continued to mine limestone up to this point.

Sarwanto and Prayitno (2015) claim that habitats for flora and fauna as well as hydrological changes in the terrain have been harmed by limestone mining operations. The ecosystem of the limestone mountains is altered by environmental deterioration, resulting in a 58.1 percent decline in the diversity and a 72.41 percent decrease in the productivity of native forage. This decline will reduce the level of productivity of goats and livestock owned by farmers in the vicinity of the limestone mountains.

To overcome this issue, it is vital to exert efforts towards boosting forage resources in limestone mountain regions by repurposing open ground previously exploited for limestone mining into locations for planting food crops. The resulting agricultural waste can then serve as supplementary feed for goats. Sarwanto and Tuswati (2020) stated that sweet potatoes are appropriate to be cultivated on former limestone mining land since they may provide many benefits besides tubers as primary products. The production of local orange sweet potatoes on former limestone mining soil fertilized with 15 tons/ha of goat compost can reach 21.1 tons/ha with an average tuber weight of 190.0 grams, tuber length of 14.1 cm, and tuber width of 4.7 cm.

Then, its waste (fresh leaves and plant stem) is one of the most valuable byproducts of sweet potatoes; it may be utilized as forage for goat feed (Sarwanto and Tuswati, 2021). The local sweet potato leaves in the limestone mountains produces 116–193 leaves per plant with a leaf width of 6.7–11.4 cm. The production of its leaf waste is 105–243 grams per plant, or around 6.6–16.6 tons/ha (Sarwanto et al 2021).

Sweet potatoes (Ipomoea batatas), according to Kebede et al (2011) and Lam (2016), are a viable food crop in tropical agroclimates. Due to their great economic value and adaptability to a variety of soil types, sweet potatoes are also preferred by the community. The results of research by Irungu et al (2017) showed that sweet potato plants have a good post-harvest regeneration rate, disease resistance, and drought resistance.

Yacout et al (2016) and Zereu et al (2014) state that the leaves, petioles and stems of sweet potato plants are of sufficient quality to be utilized as animal feed, particularly for small ruminants. According to the findings of a study conducted by Sun et al (2014), sweet potato leaves are an excellent source of antioxidants and proteins, fiber, and minerals including Ca, P, K, Mg, Fe, Mn, and Cu. Those nutrients can increase livestock production. Kebede et al (2008) and Kebede et al (2011) stated that sweet potato plants are traditional plants in tropical countries and can be provided as goat feed as a source of protein and minerals. Sweet potato plants can be used as a substitute for concentrates, where the provision reaches 50% of the total feed given to goats.

Claessens et al (2009) therefore concluded that mixed crop-livestock systems were crucial to the livelihoods of smallholder farmers in East Africa. Given that sweet potatoes serve as both a food source and animal feed, their cultivation can contribute to the economic development of smallholder farmers. Sweet potato production in livestock cropping systems is 8 tons/ha, with the amount of forage waste produced at 14.6 tons/ha. In connection with this, research on the utilization of sweet potato crop waste grown in former limestone mining areas as a substitute feed for indigenous forage for goat feed needs to be carried out.

Materials and methods

The research materials comprised foraged native fodder of the limestone mountains and local orange sweet potato waste (Ipomoea batatas), as well as male goats from the area, aged 6–7 months, with an average body weight of 16.1 ± 0.93 kg. Cynodon dactylon, Euphorbia hirta, Imperata cylindrica, Themeda arguens, Ageratum conyzoides, Hyptis capitate, Lantana camara, Mikania micrantha, Neptunea lutea, Urena lobata, Calliandra calothyrsus, Centrosema pubescens and Artocarpus heterophylus are examples of native forage found in the limestone mountains. The research was conducted in the Gombong limestone mountains located in Kebumen Regency, Central Java, Indonesia, while nutritional analysis was carried out at the Feedstuff Laboratory, Faculty of Animal Science, Jenderal Soedirman University, Purwokerto, Central Java.

In this investigation, the experimental unit was organized in a completely randomized design (CRD), and four treatments of varying percentages of sweet potato waste (0 percent, 10 percent, 20 percent, and 30 percent) were utilized. The nutrients present in the experimental meal are detailed in Table 1. The parameters that were measured are the amount of fresh and dry matter that was eaten (kg/day), how easily the dry and organic matter was digested (%), and the daily weight gain (g/day). The data obtained were analyzed by the analysis of variance method, followed by further tests using the Least Significant Difference (LSD) according to the instructions of Steel and Torrie (1993) if there were differences in the results.

Result and discussion

The results of the nutrient analysis of sweet potato plant waste on former limestone mining land are provided in Table 2.

The leaves of sweet potatoes are of higher quality than their stems or a mixture of stems and leaves, as seen in Table 2. The leaves possess an exceptional nutritional composition, as seen by their substantial crude protein level of 18.77 percent and comparatively low crude fiber content of 16.85 percent. The outcomes of the investigation remain within the expected range. They are similar to those of Kebede et al (2008), who reported that the crude protein content of sweet potato leaf waste was 19.38%. However, the results are lower than those of Murugan et al (2012), who found that it reached 26.9% and Zereu et et al2014), who found that it ranges from 20.5 to 28.4%. The result of this study is higher compared to the research conducted by Iqbal et al (2014). In addition, Iqbal et al (2014) stated that purple sweet potato leaves have a crude protein content of 12.93% and green sweet potato has a crude protein content of 16.72%. Baba et al (2017) explained that forage composition depends on light exposure, temperature, crop maturity, and plant type. Table 2 shows that sweet potato leaf protein is comparable to legume protein (An et al 2003).

An additional investigation conducted by  Onyimba  et al (2015) revealed that the crude fiber content of indigenous Nigerian sweet potato leaves reached 25.10 percent, while the average crude protein level was 20.35 percent. Meanwhile, research by Sun et al (2014) showed that the crude fiber content of 40 types of local Chinese sweet potato leaves was 9.25–14.26 g/100 g dry matter, with a crude protein content of 17.53–30.53 g/100 g dry matter.

Summary of annova digestibility and intake feed was provided in table 3.

Feed consumption (kg/day)

As indicated by the findings of this research, goats fed a variety of feed formulations consumed between 3.98 and 4.03 kg per day, with details of FP0: 3.90±0.22 kg/day, FP1: 4.03±0.22 kg/day, FP2: 4.00±0.29 kg/day, and FP3: 3.98±0.30 kg/day. FP0 (consisting entirely of indigenous forage) had the lowest forage intake, whereas FP1 (10 percent sweet potato crop waste with 90 percent indigenous forage) had the highest forage consumption.

Figure 1. Feed consumption, kg/day

The findings from the analysis of variance indicated that there was no statistically significant impact (p> 0.05) of the feed formulation (FP0, FP1, FP2, FP3) on fresh forage consumption. These results showed that the substitution of sweet potato plant waste up to a 30% level has not been able to increase feed consumption. The findings shown here are consistent with those of Sarwanto et al (2019), who demonstrated that a 75 percent substitution of dwarf elephant grass (Pennisetum purpureum) for native forage in limestone mountains had no discernible impact on daily feed intake of 3.1–3.3 kg.

Dry matter consumption (kg/day)

The daily dry matter consumption of forage for goats, depending on the feed formulation, ranges from approximately 0.69–0.76 kg or 690–760 grams, with the following details: FP0: 0.76 ± 0.04 kg/day, FP1: 0.69 ± 0.04 kg/day, FP2: 0.74 ± 0.03 kg/day, and FP3: 0.71 ± 0.07 kg/day. The results of this investigation indicated that FP2 (10 percent sweet potato plant waste + 90 percent indigenous forage) exhibited the lowest dry matter consumption of forage. In contrast, FP0 shown the highest dry matter consumption (100 percent indigenous forage). These results differ from the results of Aregheore's (2004) research, which showed dry matter consumption (100% grass) of 0.851 kg/day, (50% grass + 50% sweet potato) of 1.059 kg/day, and (75% grass + 25% sweet potato) of 1.024 kg/day. Differences in these results occur due to differences in the goats used regarding body types and weights, causing different levels of dry matter consumption of forage.

Figure 2. Dry Matter Consumption, kg/day

The findings from the analysis of variance indicated that there was no statistically significant impact (p> 0.05) of the feed formulation (FP0, FP1, FP2, FP3) on the dry matter consumption of forage. The findings of this study indicate that supplementing forage diet with sweet potato plant waste, even at a concentration of 30 percent, did not result in a significant increase in dry matter consumption. The use of dry matter in each treatment (FP0, FP1, FP2, and FP3) that is relatively the same (ranging from 17.56 to 20.58%) causes the consumption value to be no different. These results are also not different from the research of Sarwanto et al (2019), which showed that the substitution of dwarf elephant grass (Pennisetum purpureum cv. Mott) for forage indigenous to the limestone mountains up to 75% did not affect the consumption of dry matter forage, which was around 0.55–0.64 kg/day. Olorunnisomo (2008) obtained organic matter consumption of 595.82–657.73 g/day in sheep that received a balance of sweet potato leaves and tubers.

Dry Matter digestibility (DMD)

The findings indicated that the dry matter digestibility (DMD) of the forage formulations varied between 43.78 and 59.88 percent, with details of DMD for FP0: 57.05±2.59%, FP1: 59.88±1.38%, FP2: 44.62±2.66% and FP3: 43.78±1.61%. Low dry matter digestibility was found in FP2 (80% indigenous forage + 20% sweet potato waste) and FP3 (90% indigenous forage + 10% sweet potato waste), while high dry matter digestibility was in FP0 (100% indigenous forage) and FP1 (90% indigenous forage + 10% sweet potato waste).

According to the findings of Aregheore (2004), the dry matter digestibility of grass formulations with up to 75% sweet potato waste substitution is approximately 47.3–72.4 percent. The dry matter digestibility of the forage formulation in the present study ranges from 43.78 to 59.88 percent. The research of Sarwanto et al (2019) showed that the substitution of dwarf elephant grass (Pennisetum purpureum cv. Mott) as a substitute for forage indigenous to the limestone mountains up to 75% had a dry matter digestibility of 59.62–63.06%.

Figure 3. Dry Matter digestibility (DMD)

The findings from the analysis of variance indicated that the degree of substitution with sweet potato plant waste significantly impacted the digestibility of dry matter in fodder (p<0.01). The findings of this study indicate that the inclusion of sweet potato plant waste in forage diet can have an impact on the digestibility of dry matter.

The results of further tests with Least Significant Difference (LSD) showed that all forage formulations FP0, FP1, FP2 and FP3 were significantly different (p<0.01) in dry matter digestibility in vitro. Further test results showed that the forage formulation FP1 (90% indigenous forage + 10% sweet potato waste) had the highest dry matter digestibility, followed by FP0, while FP2 and FP3 had the same low dry matter digestibility.

Sarwanto et al (2022) investigated the composition of native feed in limestone mountain regions, which comprised five species of grasses, three species of legumes, ten species of leaves, and two species of trees with an in vitro dry matter digestibility ranging from 37.3 to 47.3 percent. Sarwanto et al (2021) conducted research which revealed that the sweet potato leaf waste in the limestone mining area had an in vitro dry matter digestibility ranging from 62.32% to 88.31%. Therefore, the greater the amount of substitution of sweet potato leaf waste for forage indigenous to the limestone mountains, the greater the level of dry matter digestibility. The substitution of sweet potato leaves at a maximum of 10% can increase the digestibility of dry matter, and the substitution of sweet potato leaf waste by 20–30% can reduce the digestibility of dry matter in forage feed.

According to a study conducted by Olorunnisomo (2008), the dry matter digestibility of sheep that were fed a combination of dried sweet potato forage and tubers ranged from 64.6% to 70.4%. The best level was achieved in the composition of 50% leaves and 50% tubers (70.42%). Machado et al (2021) obtained a dry matter digestibility of 71.19% with the use of 1.5 percent sweet potato in sheep that received a basic diet of ryegrass hay. Thus, the dry matter digestibility of sweet potatoes was enhanced as their utilization increased.

Dry organic matter digestibility (OMD)

The findings of this research demonstrated that the organic matter digestibility (OMD) of the forage formulation exhibits a range of 34.41 to 56.84 percent. The low digestibility of organic matter in FP2 and FP3 is 34.40–39.69%, while the higher digestibility of organic matter is in FP0 and FP1 at 53.15–56.89%. The research findings regarding the digestibility of organic matter in the forage formulation (34.40–56.84 percent) are comparable to those of Aregheore (2004), which indicate that the digestibility of organic matter in grass formulations containing up to 75 percent sweet potato waste substitution is 48.60–64.9 percent. The research of Sarwanto et al (2019) showed that the substitution of dwarf elephant grass (Pennisetum purpureum cv. Mott) for forage indigenous to the limestone mountains up to 75% level has an organic matter digestibility of 53.79–56.82%, the same as the organic matter digestibility in the research feed formulation with a sweet potato plant waste substitution of 10% (FP1), which is 56.89%.

Figure 4. Organic Matter Digestibility (OMD)

The findings from the analysis of variance indicated that the degree of substitution with sweet potato plant waste significantly impacted the digestibility of feed organic matter (p< 0.01). Additional analyses utilizing the Least Significant Difference (LSD) method revealed that the in vitro digestibility of organic matter varied considerably (p< 0.01) among forage formulations FP0, FP1, FP2, and FP3. These results showed that the forage formulation FP1 (90% indigenous forage + 10% sweet potato plant waste) had the highest organic matter digestibility, followed by FP0, FP2, and the lowest FP3.

According to a study by Sarwanto et al (2022), the in vitro digestibility of organic matter in native forage in the limestone mountain region is merely 49.8–58.5 percent. In contrast, the in vitro organic matter digestibility of sweet potato leaf waste in the limestone mining region is exceptionally high at 94.49–96.82 percent, according to a study by Sarwanto et al (2021). According to the findings of this research, the digestibility of organic matter increases as the substitution level of sweet potato leaf waste for feed native to the limestone mountains increases. The study's findings indicated that sweet potato leaves may be substituted up to a maximum of 10 percent, while the digestibility of organic matter was maintained at 56.84 percent; the substitution of sweet potato leaf waste by 20–30% could actually reduce the digestibility of organic matter in forage feed. Machado et al (2022) reported that sheep that received sweet potato supplementation up to 1.5% on a ryegrass hay-based diet had 74% organic matter digestibility. Sweet potato is rich in amylose and amylopectin (Alcazar-Alay and Meireles, 2015), which are fermentable carbohydrates. Amilopectin has a 1.6 alpha bond that is easily degraded by rumen microbes (Malaguez et al 2021), so increasing the use of sweet potatoes will increase the digestibility of organic matter. In contrast to this study, which used stem and leaf waste (vine), the maximum use was 10% to obtain the highest organic matter digestibility.

Average daily gain (g)

The average daily gain (ADG) of goats from the study on various feed formulations was 28.62–32.19 grams per day. The highest average daily gain of goats in FP1 (90% indigenous forage + 10% sweet potato waste) was 32.19 ± 1.38 g/day, followed by FP2 (80% indigenous forage + 20% sweet potato waste): 30.46±1.46 g/day, FP3 (70% indigenous forage + 30% sweet potato waste): 30.36 ± 2.61 grams/day, while the lowest was FP0 (100% indigenous), which was 28.62 ± 2.30 g/day. Aregheore's (2004) study found that goats fed a forage mixture of grass (75% + 25% sweet potato waste) gained an average of 36 grams per day. Sarwanto et al 's (2019) study found that goats fed a feed mixture of native grass of the limestone mountains (75% + 25% dwarf elephant grass) gained an average of 40 grams per day. The variation in daily body weight gain is due to variations in the goat's type, age, and starting weight.

Figure 5. Average Daily Gain (g)

The feed formulation (FP0, FP1, FP2, FP3) exhibited no significant effect (p>0.05) on the daily body weight gain of goats in the limestone mountain area, according to the analysis of variance data. According to these findings, up to 30% of the native forage in the limestone mountain region can be replaced by sweet potato waste. Solubility of protein from sweet potato with CaCl₂ and NaCl solvents at pH 6-7 ranges from 70-80% (Mu et al 2009). Megersa et al (2012) obtained different results on the use of sweet potato vines by combining them with concentrates in goat feed. An ADG of 31.2 g/day was obtained while using only sweet potato vine, and 48.6 g/day was produced when using 65 percent sweet potato vine and 35 percent concentrate.

Conclusion

Native limestone mountain forage can be substituted with sweet potato plant waste from abandoned limestone mining sites up to thirty percent of the total amount of forage fed.

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