From waste to resource: circular economy, silage and nutritional quality of melon and watermelon by-products for ruminants

1 Introduction

The sustained increase in horticultural production and the intensification of supply chains have amplified the generation of organic wastes and high moisture by-products (plant biomass and rejected fruit) whose management represents an environmental and economic challenge. These streams are characterized by high perishability, seasonal volume, and transportation and disposal costs, which favor aerobic spoilage and accelerated loss of value. On a global scale, the magnitude of the problem is reflected in widely cited estimates of food losses and waste (FAO, 2011).

In this context, the circular economy (CE) proposes moving from a linear “extract-produce-dispose” model to systems that keep materials and energy in use, reduce losses and reintroduce by-products into value chains. In the agrifood sector, this approach is articulated with strategies for the prevention and valorization of losses and waste, emphasizing that their reduction contributes to reducing environmental pressures and improving efficiency in the use of resources. Institutional documents report global loss and waste figures that reinforce the urgency of solutions based on system efficiency (FAO, 2011).

In livestock systems, a particularly robust valorization route consists of converting agro-industrial by-products and agricultural residues into feed ingredients for ruminants, provided that safety is guaranteed (pesticide residues or mineral profiles) and consistent nutritional value is demonstrated. Recent studies underline that the evaluation of chemical and mineral residues should be integrated with nutritional characterization to avoid transferring risks to the food chain (Hassan et al., 2023).

Ruminant livestock, principally cattle, sheep, and goats, occupy a distinctive position in food systems because their symbiotic rumen microbiota enable them to digest cellulose-rich plant materials that humans cannot directly utilize. Consequently, their diets are generally based on forages, supplemented where necessary with energy-, protein-, mineral-, and vitamin-rich ingredients to meet requirements for maintenance, growth, pregnancy, and milk production. This ability also permits ruminants to utilize crop residues and agro-industrial by-products; indeed, Mottet et al. (2017) estimated that approximately 86% of global livestock feed dry matter consists of materials not currently edible by humans. Nevertheless, feed quality, availability, and cost strongly influence animal productivity and the economic viability of meat and dairy systems. Maintaining a reliable supply of nutritionally adequate feed throughout the year is therefore a fundamental requirement of ruminant production and becomes particularly important where forage growth and availability fluctuate seasonally.

Forages can be consumed fresh or preserved, primarily as hay or silage. Whereas hay preservation depends on extensive drying, silage is produced by storing moist plant biomass under oxygen-limited conditions, typically after chopping and compaction. Under these anaerobic conditions, naturally occurring or added lactic acid bacteria ferment water-soluble carbohydrates predominantly into organic acids, causing a rapid decline in pH that inhibits undesirable microorganisms and stabilizes the biomass. The objective is to retain as much of the original crop dry matter, energy, and digestible nutrients as possible until feeding (Kung et al., 2018). Ensiling is an established forage-preservation technology used extensively in modern dairy and beef production, with whole-plant maize being one of the predominant silage crops worldwide; grasses, legumes such as alfalfa and clovers, and small-grain cereals are also commonly ensiled. Whole-plant maize silage, for example, combines relatively high biomass yield with fermentable carbohydrates and digestible fiber and has become a major forage in dairy cattle diets (Ferraretto et al., 2018). Preservation as silage also reduces dependence on continuous availability of fresh forage and, compared with haymaking, can reduce exposure to weather-related drying constraints.

From a sustainability perspective, these characteristics make ensiling relevant beyond conventional forage conservation. The same biological process can potentially stabilize moist, highly perishable agricultural residues that would otherwise deteriorate rapidly, thereby extending their useful life and recovering part of their remaining nutritional value. For ruminant systems, this creates a potential link between waste management and feed production: suitable by-products can be redirected from disposal into animal feeding, potentially reducing losses and partially substituting conventional feed resources. However, such substitution should not automatically be considered sustainable; its net benefit depends on preservation losses, transport and processing requirements, feed safety, nutritional value, animal performance, and the extent to which it actually displaces other feed ingredients. These considerations provide the basis for evaluating melon and watermelon residues as unconventional silage feedstocks within a circular economy framework.

Among the available technologies, ensiling stands out as an anaerobic preservation method capable of stabilizing perishable materials and preserving their nutritional value. However, its performance depends on critical variables such as dry matter, availability of soluble carbohydrates, and control of undesirable fermentations and handling during delivery; therefore, the interpretation of chemical, microbiological and organoleptic indicators is essential to evaluate silage quality and stability (Kung et al., 2018).

Melon (Cucumis melo) and watermelon (Citrullus lanatus) residues are attractive candidates within the circular logic because of their regional availability and nutritional supply potential. However, their high humidity can favor effluents and nutrient losses if conditioning strategies (pre-drying or co-silage with sorbents) are not applied, as has been documented in melon biomass (Nascimento et al., 2023c) and in watermelon plant silage as a forage option for small ruminants (Pardo et al., 2025). These crops, are among the most widely cultivated horticultural crops worldwide, generating substantial amounts of field biomass, rejected fruits, and postharvest residues each year. Because of their high moisture content and limited shelf life, a considerable proportion of these materials is lost during harvesting, grading, transportation, and commercialization, while additional residues remain in the field after harvest. Current management practices generally include field disposal, composting, landfill disposal, or occasional direct feeding to livestock, which often fail to maximize nutrient recovery and may generate environmental burdens. Within a circular economy framework, these underutilized biomass streams represent an important opportunity for valorization through ensiling, allowing nutrients to be conserved, reducing waste disposal, and partially replacing conventional feed resources for ruminants.

The objective of this review is to critically examine the available evidence on the use of melon and watermelon by-products for silage production in ruminant feeding within a circular economy framework. Specifically, the review focuses on: (1) the types of residues evaluated and their preservation through ensiling or related upgrading strategies; (2) their effects on fermentation profile, dry matter recovery, and nutritional quality; (3) the main technical constraints associated with high-moisture biomass, safety, and feed-out stability; and (4) the research gaps that limit practical adoption, including the scarcity of in vivo validation, economic assessment, and life-cycle-based sustainability analysis. The review is limited to studies addressing preservation, nutritive value, and feeding relevance of melon and watermelon residues, and does not aim to provide a broader synthesis of all fruit and vegetable by-products used in ruminant nutrition.

To provide an integrated overview of the preservation and valorization process discussed throughout this review, Figure 1 summarizes the principal stages involved in converting melon and watermelon by-products into high-quality silage within a circular economy framework.

2 Melon and watermelon by-products as silage feedstocks: preservation constraints and technical basis

Melon (Cucumis melo) and watermelon (Citrullus lanatus) production systems generate seasonal volumes of high moisture residues from field biomass (guides/leaves/stems), rejected fruit and losses due to trimming or handling (Carlos de Oliveira et al., 2023; Pardo et al., 2025). Their perishability, volume and logistical costs favor spoilage and inefficient disposal.

Under a CE lens, these challenges are interpreted as “loss points” where value is lost: prior aerobic storage, inefficient fermentation due to excess moisture (effluent and gaseous losses) and aerobic instability during delivery. Table 1 summarizes these critical points and their main control levers. In this regard, moisture control appears as the most decisive cross-cutting lever: when DM is low, effluents and gas losses increase, reducing nutrient recovery per ton of residue. Therefore, pre-drying or co-silage strategies with absorbents have a double circular role: (1) they improve the technical performance of silage and (2) they preserve value by avoiding early losses. Even with technically acceptable silage, full circularity requires safety governance (pesticides and minerals) and net benefit assessment through techno-economic analysis (TEA) and life cycle analysis (LCA) (Hassan et al., 2023).

Table 1. Leakage points and control levers for melon and watermelon waste valorization via silage in a circular economy framework.

2.1 Preservation constraints and residue-management bottlenecks

Silage is an anaerobic preservation process whose success depends on controlling dry matter (DM), availability of soluble sugars, buffer capacity, microbiota (predominance of lactic acid bacteria), compaction—sealing and handling during opening (Kung et al., 2018). In high moisture residues, DM is usually the dominant variable because it conditions effluent, losses and aerobic stability.

In the case of melon and watermelon residues, evidence agrees that moisture control defines the feasibility frontier: pre-drying or dehydration, fibrous forage with absorbent products or additives (urea) are recurrent levers to improve preservation and reduce losses (Nascimento et al., 2023a,b; Durusoy and Çerçi, 2025).

In addition to physical conditioning and conventional additives, fibrolytic enzymes such as cellulases, xylanases, and pectinases have emerged as promising tools for improving the ensiling of high-moisture biomass. These enzymes partially hydrolyze plant cell wall polysaccharides, increasing the availability of fermentable sugars for lactic acid bacteria, thereby accelerating acidification, improving nutrient preservation, and reducing fiber concentrations. Although most available evidence has been generated using conventional forage crops, these mechanisms could also enhance the preservation of melon and watermelon residues, whose high moisture and structural carbohydrate content often limit fermentation efficiency. Nevertheless, direct evidence for cucurbit by-products remains limited, and future studies should evaluate enzyme formulations, economic feasibility, and their integration with microbial inoculants under practical feeding systems (Kung et al., 2018; Li et al., 2023; Qiu et al., 2024).

3 Nutritional quality of melon and watermelon silage

Beyond fermentative feasibility, circular valorization requires demonstrating nutritional utility through quantifiable parameters. In the available evidence, DM (determined by fraction and conditioning) governs much of the variation in detergent fiber, soluble carbohydrates and EE, with direct implications on potential intake, aerobic stability and energy density.

3.1 Melon silage: fiber, potential energy and fruit inclusion trade-offs

By increasing the proportion of fruit, DM as low as 130 g/kg (100% fruit, fresh basis) has been described, with increases in water soluble carbohydrates (WSC) up to 217 g/kg DM and EE in the range 73–88 g/kg DM, associated with the contribution of seeds. In the same scheme, NDF averaged −605 g/kg DM and ADF decreased from 308 g/kg DM (10% fruit) to 238 g/kg DM (20% fruit). The addition of 1.5% urea raised CP from −59 to −70 g/kg DM.

In melons, the fruit increases WSC and EE but can reduce DM to levels that favor effluents; therefore, strategies to increase DM seek to preserve value and stabilize feed use. To maintain the sustainability of the system, these benefits must be integrated with safety and in vivo trials (Hassan et al., 2023).

These values suggest a dual profile: higher soluble fraction (fermentable energy) but with risks of effluent and aerobic instability in high moisture and high substrate scenarios. EE close to 80–90 g/kg DM can increase energy density, but requires inclusion control to avoid exceeding operational fat limits in ruminants and to avoid compromising silage stability. Pre-drying—dehydration emerges as a stabilizing strategy. When biomass was dehydrated to −40% DM and combined with moderate levels of fruit (10%), a more favorable balance was described at pH 4.1–4.4 (Nascimento et al., 2023a).

3.2 Watermelon silage: plant vs. fruit comparison and changes after silage

For the whole watermelon plant in PVC pipe microsilos, the following values were reported (Durusoy and Çerçi, 2025): DM 147 g/kg, CP 226 g/kg DM, EE 14 g/kg DM, NDF 367 g/kg DM, ADF 242 g/kg DM and WSC 191 g/kg DM. After ensiling the plant, DM increased to 157 g/kg, CP decreased to 211 g/kg DM and EE increased to 30.9 g/kg DM; NDF and ADF were maintained (363 and 264 g/kg DM) and WSC decreased to 169 g/kg DM (Durusoy and Çerçi, 2025).

In fruit silage, the following were reported: 21–23% DM with CP 209 g/kg DM, EE 160.8 g/kg DM, WSC 81.2 g/kg DM, ME 11.6 MJ/kg DM, and pH 3.79; 27–29% DM with CP 261 g/kg DM, EE 167.2 g/kg DM, WSC 73.6 g/kg DM, ME 12.1 MJ/kg DM, and pH 3.96; and 33–35% DM with CP 320 g/kg DM, EE 199.3 g/kg DM, WSC 64.3 g/kg DM, ME 12.1 MJ/kg DM, and pH 4.27 (Pardo et al., 2025). The watermelon plant retains a moderate NDF/ADF profile, while the ensiled fruit concentrates EE and ME, which can increase energy density, but with the need to control inclusion and balance of effective fiber.

These data position fruit silage as the most concentrated ingredient (high EE and ME −11.6–12.1), useful to increase energy density, but which requires effective fiber balance and inclusion management.

3.3 Comparative analysis with other byproducts used in ruminant feed

Compared with other agricultural by-products used in ruminant feeding (Table 2), melon and watermelon residues fit within the group of high-moisture resources whose value depends not only on their chemical composition, but also on the feasibility of their preservation and safe incorporation into feeding systems. Similar to other fruit and vegetable by-products, they offer an opportunity to recover nutrients from highly perishable streams and redirect them into livestock production; however, in both crops, moisture remains the dominant constraint because it conditions effluents, nutrient losses, aerobic stability, and logistic loads. In melon, the available evidence indicates a material with variable dry matter, generally high fiber and moderate crude protein, whose nutritional utility improves when conditioning strategies such as pre-drying, absorbent co-silages, or additives are applied. In watermelon, the evidence is more limited, but points to a forage resource with greater crude protein concentration and lower fiber than melon in some fractions, although equally dependent on dry matter adjustment and management control. Therefore, relative to more established by-products, the comparative limitation of cucurbit residues lies less in the absence of nutritive potential than in the need to standardize preservation, govern variability, and demonstrate net benefit under practical feeding conditions.

Table 2. Comparative nutritional value of selected byproducts used in ruminant feed.

DM, dry matter; CP, crude protein; NDF, neutral detergent fiber; EE, ether extract; NFC, non-fiber carbohydrates; NSC, non-structural carbohydrates; GE, gross energy; ME, metabolizable energy; NR, not reported. Representative values compiled from peer-reviewed sources; values are reported on a dry matter basis unless otherwise indicated.

3.4 Integrative discussion: implications for forage and ingredient substitution

Silages based on plant biomass tend to have more forage profiles (moderate-high NDF/HDF; low-moderate EE) and require DM correction to minimize losses. On the other hand, silages with a high proportion of fruit, particularly watermelon, resemble an energy ingredient because of their high EE, with higher management requirements (aerobic stability) and effective fiber balance.

4 Production performance of ruminants fed melon and watermelon silages

The studies summarized in Table 3 demonstrate that melon and watermelon residues have considerable potential as alternative feed resources for ruminants; however, the current evidence is substantially stronger for their preservation characteristics and in vitro nutritional value than for their effects on animal productivity.

Table 3. Scientific evidence on melon and watermelon silage or closely related preserved products for ruminants.

An important conclusion from Table 3 is the almost complete absence of direct in vivo evidence for conventionally ensiled melon and watermelon residues. None of the verified silage studies evaluated weight gain, gain-to-feed ratio, residual feed intake, carcass yield, carcass composition, meat color, tenderness, marbling, water-holding capacity, lipid oxidation, milk yield, milk composition, or somatic cell count (Figure 2). Thus, the reported improvements in digestibility, energy concentration, and fermentation profile should be interpreted as indicators of nutritional potential rather than proof of productive benefit. Voluntary intake may be affected by acidity, moisture, particle size, aroma, fermentation products, and aerobic deterioration, variables that cannot be adequately predicted using chemical composition alone.

The animal-performance studies conducted by Fayed et al. (2019) and Soliman et al. (2020) provide relevant but indirect evidence. Both studies evaluated biologically treated watermelon vines rather than conventionally ensiled material. Fayed et al. (2019) reported that fungal treatment improved the nutritive value of watermelon vines and supported satisfactory growth in lambs at moderate inclusion levels. Similarly, Soliman et al. (2020) observed that partial replacement of berseem hay with biologically treated watermelon vines maintained dry matter intake and supported milk production and nutrient digestibility, particularly at low or moderate replacement rates.

Overall, the available literature indicates that melon and watermelon by-products can be transformed into nutritionally valuable silages when their high moisture content is adequately controlled. Rejected melon fruit may improve the energy value and in vitro digestibility of conventional forage silages, whereas whole-plant watermelon silage may serve as a moderate-quality forage. Fruit-rich watermelon silages may provide greater energy density but require careful control of dietary fat and effective fiber. Despite these advantages, the evidence base remains insufficient to define optimal dietary inclusion rates or predict animal production responses. Future research should employ adequately replicated in vivo trials comparing isoenergetic and isonitrogenous diets, so that the specific effects of melon or watermelon silage can be distinguished from changes in overall dietary nutrient density. Studies should measure voluntary intake, apparent total-tract digestibility, ruminal fermentation, microbial protein synthesis, nitrogen balance, methane production, daily weight gain, feed conversion efficiency, carcass characteristics, meat quality, milk yield, milk composition, and animal health. Aerobic stability during feed-out, mycotoxin risk, pesticide residues, mineral accumulation, economic feasibility, and life-cycle environmental impacts should also be quantified. Such information is necessary before melon and watermelon silages can move from promising circular-economy feedstocks to scientifically validated components of commercial ruminant diets.

5 Comparative synthesis of key studies and implications for circular economy

5.1 Melon: recovery route, evidence, and critical synthesis

In melon, the recovery route described in the literature usually follows: (1) capture and segregation of the residue (plant biomass vs. fruit), (2) conditioning to manage moisture and fermentability (pre-drying, co-silage with sorbents or chemical amendments), (3) anaerobic stabilization (ensiling) and (4) use, with predominance of in vitro evaluations as an approximation of nutritional value. Most work is gate-to-gate and does not close with animal performance or life-cycle accounting, so circularity is demonstrated mainly as technical feasibility and nutrient retention, rather than quantified net benefit (Nascimento et al., 2023a).

5.1.1 Evidence and expected results

(a) Co-silage of rejected fruit with forages (catch + mix strategy). The inclusion of rejected melon fruit in silages with sorghum is reported as a practical option to divert discarded fruit to conserved forage while maintaining acceptable fermentation indicators (Carlos de Oliveira et al., 2023). However, the literature highlights that DM recovery and aerobic stability are not always reported with the same rigor and, in several cases, zootechnical results are lacking.

(b) Pre-drying or dehydration: effluent control and DM recovery. In factorial designs comparing fresh vs. dehydrated biomass (~40% DM), raising DM consistently improves DM recovery and reduces losses associated with moisture, reinforcing that physical conditioning can be decisive when the residue is very watery (Nascimento et al., 2023a).

(c) Co-silage with absorbents: logistical alternative to pre-drying. The use of absorbent co-products (ground corn/sorghum) increases DM and improves preservation metrics; in addition, it buffers the negative effects of high proportions of fruit, which tend to increase effluents and gas losses (Nascimento et al., 2023b).

(d) Urea: The addition of urea is proposed as a route for nitrogen enrichment and potential fermentation control, but requires technical governance due to the risk of ammonia accumulation, palatability and safety; it also requires in vivo validation to translate the increase in equivalent protein into consistent productive responses.

5.1.2 Critical synthesis for melon

Overall, the message from melon studies is clear: moisture-driven losses are the main limiting factor in silage valorisation. Therefore, pre-drying and sorbents are complementary methods of increasing nutrient retention per ton of residue. Urea provides an opportunity for chemical enhancement, albeit with increased operational and safety complexity. Priority areas include standardizing effluent reporting, gaseous losses, dry matter (DM) recovery and aerobic stability (Nascimento et al., 2023a,b; Kung et al., 2018).

5.2 Watermelon: available evidence and key findings

5.2.1 Available evidence and types of studies

For watermelon, the evidence is minor and concentrated on (1) fermentative quality of silage and in vitro digestibility, (2) nutritional characterization and safety constraints (minerals and pesticide residues) when considering by-products as substitutes for conventional ingredients, and (3) a subset of studies with animal performance when biological enhancement is applied to the guidelines (Fayed et al., 2019; Soliman et al., 2020; Hassan et al., 2023; Durusoy and Çerçi, 2025; Pardo et al., 2025).

5.2.2 Key findings

(a) DM as a control variable. Adjusting the DM level of watermelon residue is associated with improvements in silage parameters and in vitro digestibility, coinciding with the pattern observed in melon (Durusoy and Çerçi, 2025).

(b) Partial substitution of forages. Watermelon plant silage is proposed as an option for partial replacement of conventional forages in goat diets, mainly with in vitro evidence; however, harvesting can introduce variability (increased ash due to soil contamination), so management and field validation protocols are required (Pardo et al., 2025).

(c) Waste safety and governance. Circular valorization should not transfer the risk to the food chain: the need to monitor pesticide residues and mineral profiles in agro-industrial by-products destined for ruminants is emphasized (Hassan et al., 2023).

(d) Beyond classical silage: Biological improvement (fungal treatment) of watermelon guides has been evaluated as an alternative to increase their nutritive value and enable forage substitutions; productive results are dependent on the level of inclusion and process control (Fayed et al., 2019; Soliman et al., 2020).

The comparison evidences a methodological pattern (Table 4): the melon literature has advanced more on loss accounting (effluents, gases, DM recovery) and on the role of conditioning (pre-drying or sorbents), while in watermelon it highlights the in vitro evaluation and the exploration of complementary routes such as biological upgrading of guides. In both crops the same circular gap persists: there is a lack of closure with animal performance, aerobic stability under real supply conditions and net benefit evaluation considering conditioning and logistic loads. In addition, the work of Hassan et al. (2023) reminds us that circularity must integrate safety and traceability to avoid transferring risks to the food system.

Table 4. Comparative synthesis of key studies on silage/valorization of melon and watermelon residues and their implications for circular economy.

The available literature on melon by-products has progressively evolved from evaluating simple co-ensiling strategies toward optimizing preservation techniques capable of improving nutrient conservation and reducing fermentation losses. Collectively, these studies demonstrate that the principal challenge is not the nutritional value of melon residues but rather their exceptionally high moisture content, which compromises fermentation efficiency and nutrient recovery.

The first study specifically addressing the practical utilization of rejected melon fruits was conducted by Carlos de Oliveira et al. (2023). The authors evaluated the incorporation of discarded melon fruits into sorghum silage as a strategy to divert fruit waste from disposal while improving the nutritive value of conventional forage. Different inclusion levels of rejected melon fruits were mixed with chopped sorghum and preserved under anaerobic conditions. Following the fermentation period, the silages were evaluated for chemical composition and fermentation characteristics. The inclusion of melon fruits increased the concentration of soluble carbohydrates without negatively affecting silage fermentation, producing acceptable pH values and satisfactory preservation quality. The study demonstrated that co-ensiling represents a practical alternative for utilizing rejected fruits generated during commercial production. However, the authors did not quantify dry matter recovery, aerobic stability, or animal performance, limiting conclusions regarding the overall efficiency of nutrient recovery within a circular economy framework.

A more detailed evaluation of moisture management was subsequently presented by Nascimento et al. (2023a), who investigated whether increasing dry matter content before ensiling could improve the preservation of melon plant biomass. Using a factorial experimental design, fresh biomass was compared with dehydrated biomass adjusted to approximately 40% dry matter prior to ensiling. After the fermentation period, silages were analyzed for fermentation profile, microbial populations, nutrient composition, and dry matter recovery. Dehydration substantially reduced effluent production, improved dry matter recovery, and resulted in more desirable fermentation characteristics, including lower pH values and greater nutrient preservation. These findings clearly demonstrated that physical conditioning before ensiling is one of the most effective strategies for stabilizing melon residues. Nevertheless, the study remained limited to laboratory-scale silos and did not include animal performance, economic assessment, or life-cycle analysis.

Recognizing that dehydration may not always be feasible under commercial conditions, Nascimento et al. (2023b) explored co-ensiling melon biomass with absorbent ingredients, principally corn bran, to increase dry matter concentration without requiring artificial drying. The study evaluated different biomass-to-fruit proportions with and without absorbent supplementation. Fermentation quality, microbial populations, nutrient composition, and fermentation losses were assessed after ensiling. The addition of corn bran successfully increased dry matter concentration, reduced fermentation losses, and improved overall silage stability, particularly when higher proportions of melon fruits were included. Although these results support co-ensiling as an economically attractive preservation strategy, the study did not evaluate aerobic stability during feed-out or validate the nutritional responses in animals.

In a complementary study, Nascimento et al. investigated the use of urea as a chemical additive during ensiling of melon biomass. Different levels of urea were incorporated into the silage to improve nitrogen concentration and potentially influence fermentation dynamics. After the ensiling period, chemical composition, fermentation profile, and microbial characteristics were determined. Urea supplementation increased crude protein concentration and modified several fermentation characteristics while maintaining acceptable silage quality. However, the authors emphasized that excessive ammonia production, possible reductions in palatability, and the need for careful management require cautious application under farm conditions. Furthermore, improvements in crude protein concentration were not validated through animal performance trials, leaving uncertainty regarding their practical nutritional significance.

Taken together, these investigations consistently identify moisture management as the principal determinant of successful melon silage production. Physical conditioning through dehydration, absorbent co-ensiling, and selected additives all contribute to improving preservation efficiency; however, the literature remains dominated by laboratory evaluations. Future studies should integrate in vivo animal responses, aerobic stability during feed-out, techno-economic assessment, and life-cycle analysis to quantify the true circular benefits of these preservation strategies.

Compared with melon, considerably fewer studies have evaluated watermelon by-products for silage production. Existing research has focused primarily on optimizing fermentation, assessing nutritional quality, improving digestibility, and ensuring feed safety, with relatively limited validation under practical livestock production systems.

One of the earliest contributions was reported by Fayed et al. (2019), who investigated biological treatment of watermelon vines using lignocellulolytic fungi before their inclusion in diets for growing lambs. The fungal treatment partially degraded structural carbohydrates, increasing digestibility and improving the nutritional value of the biomass. Feeding trials demonstrated improvements in growth performance compared with untreated material, suggesting that biological upgrading may represent an alternative to conventional ensiling for fibrous watermelon residues. Nevertheless, the effectiveness of this approach depended on careful process control and was evaluated under relatively controlled experimental conditions.

Building upon this concept, Soliman et al. (2020) evaluated biologically treated watermelon vines as a forage component in diets for dairy cattle. Watermelon vines were treated with selected fungal cultures prior to incorporation into experimental rations, and productive performance, feed utilization, and nutrient digestibility were subsequently assessed. The biological treatment enhanced digestibility and supported satisfactory animal performance, demonstrating that watermelon vines can partially replace conventional forages. However, the additional processing requirements and limited information regarding economic feasibility restrict immediate commercial adoption.

A broader perspective was provided by Hassan et al. (2023), who evaluated fifteen agro-industrial by-products, including watermelon silage, as potential substitutes for conventional feed ingredients for small ruminants. The study combined chemical composition, mineral profiling, pesticide residue determination, and in vitro ruminal fermentation to assess both nutritional value and feed safety. Several by-products successfully replaced conventional ingredients without negatively affecting ruminal fermentation. However, considerable variability in mineral composition was observed, and pesticide residues exceeding regulatory limits were detected in some materials, including watermelon silage. The authors concluded that successful circular utilization of agro-industrial residues requires not only adequate nutritional quality but also systematic monitoring of chemical contaminants, mineral composition, and batch traceability to ensure feed safety.

More recently, Durusoy and Çerçi (2025) specifically investigated the effect of dry matter concentration on watermelon silage quality. Watermelon residues were ensiled at different dry matter levels, after which fermentation characteristics, chemical composition, and in vitro digestibility were evaluated. Increasing dry matter concentration consistently improved fermentation quality, reduced undesirable fermentation, and enhanced in vitro digestibility, confirming that moisture management is equally critical for watermelon as for melon. However, the study was limited to laboratory-scale fermentation and did not evaluate animal responses or commercial-scale implementation.

The most comprehensive evaluation currently available was reported by Pardo et al. (2025), who examined the chemical composition and in vitro nutritional value of watermelon plant silage intended for Murciano-Granadina goats. Whole-plant watermelon biomass was ensiled and subsequently analyzed for nutrient composition, metabolizable energy, fiber fractions, fermentation quality, and in vitro digestibility. The resulting silage exhibited moderate neutral detergent fiber concentrations, relatively high crude protein, acceptable fermentation characteristics, and satisfactory digestibility, indicating considerable potential as an alternative forage resource. Nevertheless, the authors emphasized that harvesting procedures may substantially influence ash concentration because of soil contamination, and no in vivo feeding trials were conducted to validate animal performance or determine practical inclusion rates.

Overall, the available evidence demonstrates that watermelon by-products possess considerable potential for incorporation into ruminant feeding systems, either through conventional ensiling or biological upgrading. Similar to melon, successful preservation depends primarily on adequate dry matter management. However, additional considerations—including feed safety, contaminant monitoring, batch traceability, aerobic stability, and animal performance—remain insufficiently investigated. Consequently, future research should integrate preservation technology with nutritional validation, economic analysis, and environmental assessment to fully quantify the contribution of watermelon by-products to circular livestock production systems.

6 Benefits (value generated) and expected outcomes under CE

The potential benefits of integrating melon and watermelon are organized into three categories. First, environmental: reduction of losses and less pressure for disposal of perishable waste; in addition, partial substitution of conventional ingredients or fodder (benefit to be quantified with life cycle assessments). Second, economic: conversion of a cost (residue) into a conserved input and the possibility of cushioning fodder seasonality, conditioned by logistic and conditioning costs. Third, social and safety: creation of local food alternatives and employment opportunities; simultaneously, sustainability requires monitoring of residues (pesticides, minerals) and safe inclusion criteria (Hassan et al., 2023; Kung et al., 2018).

7 Future directions and research gaps

The consistently emerging research agenda includes: (1) in vivo closure (intake, rumen health, production) in goats, sheep and cattle with realistic rations and sufficient periods; (2) standardization of critical metrics (effluent, gaseous losses, DM recovery and aerobic stability); (3) optimization of co-silages (sorbents, plant/fruit ratios, inoculants and additives) under field conditions; (4) explicit assessment of circularity through TEA and LCA, incorporating pre-drying and transport energy; and (5) governance and safety with sampling protocols, batch traceability and safe inclusion guidelines (Nascimento et al., 2023a,b; Hassan et al., 2023; Durusoy and Çerçi, 2025).

8 Conclusion

Overall, the evidence reviewed indicates that melon and watermelon residues represent a viable feedstock for silage production within a circular economy framework, by allowing to transform highly perishable streams into a conservable feed resource for ruminants. However, technical performance and usable value depend critically on dry matter control, as high moisture increases effluents, nutrient losses and aerobic instability. In melon, pre-drying and co-silking with absorbent materials emerge as consistent strategies to stabilize fermentation and preserve nutrients, while the use of urea offers a route to nitrogen enrichment with greater demands for management and safety assessment. In watermelon, evidence supports both the use of the ensiled plant as a forage option and the potential of silages with fruit fractions with higher energy density; however, the latter require strict control of inclusion and effective fiber balance due to their high content of ethereal extract.

Generative AI statement

The author(s) declared that Generative AI was not used in the creation of this manuscript.

Any alternative text (alt text) provided alongside figures in this article has been generated by Frontiers with the support of artificial intelligence and reasonable efforts have been made to ensure accuracy, including review by the authors wherever possible. If you identify any issues, please contact us.

Publisher's note

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

Supplementary material

The Supplementary Material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/frsus.2026.1809417/full#supplementary-material

Supplementary material Supplementary material at the source

Footnotes

Edited by: Ved Prakash Ranjan, Indian Institute of Technology Jammu, India

Reviewed by: Michael D. Flythe, Agricultural Research Service, United States

Rajneesh Thakur, Guru Angad Dev Veterinary and Animal Sciences University, India